WO2018037230A1 - Pyridyl-ethylenedioxy-thiophene derivatives as transparent conductive material - Google Patents

Abstract

Described herein is a molecule for use as a conductive coating, the molecule comprising pH neutral or substantially neutral functionalities and presenting chemical diversity, transparency in the UV-Vis spectrum and solubility in common organic solvents. Also described herein is film prepared from a solution of a molecule described herein, a method of tuning the properties of a molecule described herein, a transparent electrode and an organic electronic device comprising a molecule described herein.

Description

PYRIDYL-ETHYLENEDIOXY-THIOPHENE DERIVATIVES AS TRANSPARENT CONDUCTIVE

MATERIAL

Field of the Invention

The present invention is directed to the field of organic electronics, in particular transparent conductive materials for use in optoelectronics. Background to the Invention

Transparent conductive films are employed in multiple electronics applications such as liquid crystal displays, OLEDs, touchscreens and photovoltaics, where a highly conductive material that does not block light is required. Transparent conducting metal- oxides, particularly indium tin oxide (ITO) are the most widely used materials due to their high conductivity and low visible light absorption coefficient when deposited as thin films. However, the high demand of ITO has caused prices to rise and it presents poor mechanical flexibility. Therefore, alternative materials that present low resistivity, transparency to visible light and further properties such as thermal stability, flexibility or ease of processability are desirable. Some materials are currently employed to form transparent conductive films, such as conductive polymers, metallic nanowires, carbon nanotubes or graphene.

Organic materials are widely available and present advantages over their inorganic counterparts such as low-cost processing, mechanical flexibility and the possibility to tune their properties through structural modification or different processing techniques. Solution processable functional organic materials can be easily deposited on multiple surfaces, (including flexible substrates) by means of a variety of simple deposition techniques, leading to low-cost, lightweight and even flexible organic electronic devices. Printing processes of organic materials have been optimised to achieve high throughput and low temperature fabrication of large area flexible electronics. However, organic materials have limitations in electronic applications due to lower carrier densities and charge mobilities than established inorganic transparent conductive materials.

PEDOT:PSS, a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) with polystyrene sulfonic acid (PSS), is currently the go-to material for applications in solution-processed organic electronics where a highly conductive yet transparent material is needed. It is employed in a wide range of applications such as antistatic coatings for plastic films in electronic packaging and photographic films, counter- electrodes in capacitors, transparent and flexible electrodes in electronic applications such as touch screens, transparent electrodes and/or hole injection layers in OLEDs for displays and lighting applications, hole transport layers and/or transparent electrodes in organic solar cells.

However, the PSS groups are inherently acidic and hygroscopic. Upon exposure to air, water can be absorbed onto films comprising PEDOT:PSS and generating an aqueous acidic environment. This acidity is detrimental for device performance as it can cause degradation of adjacent layers of organic functional materials and/or etching of Indium Tin Oxide (ITO) electrodes, which are commonly used in organic electronic applications. ITO electrodes are very sensitive to acidity, leading to diffusion of oxygen out of the ITO electrode into the active polymer layer of the device. This hinders the performance of organic electronic devices and reduces their stability in atmospheric conditions.¹ It is amongst the objects of the present invention to provide novel transparent conductive materials for electronic applications.

Summary of the Invention

The present invention is based on the development of novel compounds for transparent conductive coatings. According to a first aspect there is provided a molecule for use as a conductive coating, the molecule having the structure:

R may be present or absent. When present R may be selected from the group comprising an alkyl chain, an oligoether chain, an aliphatic alcohol and/or an amine functionality or combinations thereof; Xi-X₄ may be selected from the group comprising

¹ M.P. de Jong, L J. van Ijzendoom, M. J. A. de Voigt, Applied Physics Letters, 77, 14, 2000 H, an electron-donating group and/or an electron-withdrawing group; Y may be selected from the group comprising H, an electron-donating carbocyclic aromatic ring, an electron-donating aromatic heterocycle, an electron-withdrawing aromatic carbocyclic ring and/or an electron-withdrawing aromatic heterocycle; and wherein R is presnet, A^" is present and may be any suitable counter ion.

The R substituents may comprise an alkyl group, such as a linear and/or branched alkyl chain. Linear alkyl chains have the general formula C_nH₂n₊i . Linear alkyl chains may have a number of carbon atoms (n) ranging from 1 to 20. For example, linear alkyl chains may comprise C₃H₇, C₄H₉, CsHn , C₆H₁₃, C₇H₁₅, C₈H₁₇, C₉H₁₉, C₁₀H₂₁ , C₁₂H₂₅, C₁₆H₃₃ and/or C₁₈H₃₇. Branched alkyl chains are isomers of linear alkyl chains with general formula C_nH_2n+i in which the alkane has alkyl substituents along its chain. Examples of branched alkyl chains comprise, but are not limited to 2-ethylhexyl, 3- ethylhexyl, 4-ethylhexyl.

The R substituents may comprise a linear and/or branched alkyl chain functionalised with a polar substituent. For example, the R substituents may comprise linear or branched oligoethers, linear or branched alcohols and/or linear or branched amines.

Oligoethers may have the formula ⁿ , wherein n may be selected from 1 to 10 repeat units. For example oligoethers envisaged herein may comprise solubilising chains with n = 2, 3, 4, 5, 6, 7 or 8. For example, R substituents may comprise a branched oligoether comprising a linear alkyl functionality with oligoether substituents along the chain. Some examples of branched alkyl chains functionalised with oligoether functionalities comprise, but are not limited to

Aliphatic alcohol substituents have a general formula (CnH₂n₊i-x)(OH)_x and may comprise a linear or branched alkyl chain as defined above with one or more hydroxyl substituent. Alcohols envisaged herein may comprise solubilising chains with n = 1 to 20, for example n = 1 , 2, 3, 4, 5, 6, 7, 8, 10, or 12. Alcohols envisaged herein may comprise any number of hydroxyl substituents, for example x = 1 , 2, or 3. For example, alcohols envisaged herein may comprise, but are not limited to C1 H2OH, C₂H₄OH, C₃H₆OH, C₅H₁₀OH, C₅H₉(OH)₂, C₆H₁₂OH, C₇H₁₄OH, C₈H₁₆OH, C₆H (OH)₂, C₆H₁₀(OH)₃,C₉H₁₆(OH)₃, and the like.

Amine substituents may comprise primary, secondary or tertiary amines. Aliphatic primary amine substituents have a general formula -C_nH_2n(NH₂). Aliphatic secondary amine substituents have a general formula -NH(C_nH_2n+i ). Aliphatic tertiary amine substituents have a general formula -N(C_nH_2n+i ) (C_mH_2m+1). Amines envisaged herein may comprise any length of alkyl chain chains. For example, amines envisaged herein may have n = 1 -20 and/or m = 1 -20. The alkyl chains of the amine substituents may be linear or branched. Amine substituents may one or more amine substituent. Amines envisaged herein may comprise any number of amine substituents, for example 1 , 2, 3 and the like. Examples of amine substituents may comprise, but are not limited to:

Examples of electron-donating groups may comprise, but are not limited to

O O =\

— cf -NR₂ , -NH₂ ,— OH ,— OR , — NHCR — OCR — R — <λ > — CH=CR₂ Examples of electron-withdrawing groups may comprise, but are not limited to o O O O O O

— N-0 -NR, -Nl- -S- OH — C≡N -CF₃ — CCI — COH COR — CR — CH

Examples of electron donating aromatic carbocyclic rings comprise, but are not limited to aryl units, such as phenylene or fluorene moieties with or without electron donating substituents. For example, electron donating carbocyclic aromatic rings comprise, but are not limited to:

Examples of electron withdrawing aromatic carbocyclic aromatic rings comprise, but are not limited to aryl units substituted with electron-withdrawing groups, such as cyanobenzene or nitrobenzene.

Examples of electron donating aromatic heterocycles comprise, but are not limited to:

Examples of electron withdrawing heterocycles comprise, but are not limited to:

Some electron withdrawing heterocycles may be attached to the molecules described herein on more than one position. For example, a may be attached at the 2-, 3- and/or 4- positions; b may be attached at the 2-, 3- and/or 5- positions; c may be attached at the 2- and 5- positions, d and e may be attached at the 4- and 7- positions, f may be attached at the 2, 5, 8 and 1 1 positions and g may be attached at the 4 and 10 positions. When present, suitable counterions may comprise, but are not limited to F^",CI^", Br^", , PF₆-, BF₄ ^", SbF₆ ^" TsO^", MsO^".

In one embodiment, the molecule has the general structure shown in Figure 1 , wherein XrX₄ are H, Y is H, R is a linear alkyl chain and A^" is Br^" or .

In another embodiment, the molecule has the general structure shown in Figure 1 , wherein XrX₄ are H, Y is H, R is a branched alkyl chain and A^" is Br^" or I^".

In yet another embodiment, the molecule has the general structure shown in Figure 1 , wherein X X₄ are H, Y is H, R is an oligoether chain, such as

and A^" is Br^" or I^".

In yet another embodiment, the molecule has the general structure shown in Figure 1 , wherein XrX₄ are H, Y is H, R is an alcohol or an amine functionality and A^" is Br^" or I^". The alcohol may be a linear or a branched alcohol. The alcohol may be a primary alcohol. The alcohol may be a secondary alcohol. The alcohol may be a tertiary alcohol. The amine may be a linear amine. The amine may be a branched amine. The amine may be primary, secondary or tertiary. The molecules described herein may be small molecule organic semiconductors. Small molecule organic semiconductors may have a molecular weight lower than 1000. Small molecule organic semiconductors may comprise a low number of conjugated monomers. Small molecule organic semiconductors may comprise between 2 and 20 conjugated monomers. For example, the molecules described herein may comprise between three and six conjugated monomers. The molecules described herein may be heterocyclic oligomers.

The molecules may be monodisperse. The molecules may comprise a core comprising a bisEDOT unit and a pyridine unit. Advantageously, devices fabricated with monodisperse materials usually present more reproducible outputs than devices fabricated with polymers presenting polydispersity. The molecules described herein may be pure. Advantageously, devices prepared with pure organic materials can be more stable than devices prepared with materials comprising impurities, since these impurities can lead to degradation of the organic materials. Advantageously, the molecules described herein may present chemical diversity. The molecules described herein may present functionalisation sites in their molecular structure. The molecules described herein may present a functionalisation site at the 1 - position of the pyridine (i.e. the N position). This functionalisation site is named R in the general molecular structure of the molecules. The molecules described herein present functionalisation sites at the 2- 3-, 5- and/or 6- positions of the pyridine unit. These functionalisation sites are named Xi-X₄ in the general molecular structure of the molecules. The molecules described herein may present a functionalisation site at the a position of the terminal EDOT unit. This functionalisation site is named Y in the general molecular structure of the molecules. The molecules described herein may be functionalised by adding substitutents at the functionalisation sites of the molecules. Beneficially, the presence of functionalisation sites in the molecular structure enables tuneability of the molecules described. Therefore, advantageously the molecules described herein may be tunable. The molecules described herein may be capable of structural modifications to tailor their properties to each target application. For example, the R substituent of the molecules may be changed to adjust the solubility of the molecules in different solvents. The R substituent of the molecules may be changed to tune the morphology and/or molecular packing of films of the molecules. The R, X and/or Y substituents of the molecules may be changed to alter the bandgap of the molecules. For example, adding a conjugated monomer at the Y functionalisation site may lead to a reduction of the bandgap of the molecules through extension of the conjugation length. The Highest Occupied Molecular Orbital (HOMO) and Lowest Occupied Molecular Orbital (LUMO) energy levels of the molecules described herein may be tuned by adding electron donating and/or electron withdrawing groups to the functionalisation sites of the molecules. Electron donating groups may increase the HOMO energy level of the molecules. Electron withdrawing groups may decrease the LUMO energy level of the molecules.

The molecules and/or materials, such as the conductive films described herein may be transparent in the ultraviolet-visible (UV-Vis) light spectral region (from 190 to 750 nm). Transparent materials allow a percentage of incident light in a certain spectral region (transmittance %) to pass through them. Typically the molecules and/or materials made with molecules of the present invention are >50%, such as >60%, 70%, 80% or more transparent, as readily tested by the skilled reader.

The physical, chemical and/or electrical properties of the molecules described herein may be modified by chemical functionalisation of the molecules. Advantageously, the physical, chemical and/or electrical properties of the molecules described herein may be fine-tuned for each required application via functionalisation of their chemical structure, as described above. The physical and/or electrical properties of the molecules described herein may be modified by physical processing. For example, the physical and/or electrical properties of the molecules described herein may be modified by solvent treatment, solvent vapour annealing, thermal annealing, plasma pre- treatment of the substrate, encapsulation, deposition method, molecular self-assembly and the like. Thus, the molecules described herein may present tunable conductivity, tunable electronic levels and/or tunable processability in different solvent mediums. The molecules described herein may be soluble in common organic solvents. For example, the molecules described herein may be soluble in methanol, ethanol, acetone, acetonitrile, chloroform, dichloromethane, carbon tetrachloride, chlorobenzene, cyclohexane, diethyl ether, ethyl acetate, hexane, toluene, dimethyl sulfoxide (DMSO), tetrahydrofuran and the like. The molecules described herein may be soluble in water-miscible alcohols. The solubility of the molecules in different solvents may be modified by structural modification. The solubility of the molecule in a solvent may be altered by changing the R substituent of the pyridine. For example, the solubility of the molecules in each solvent may be tailored by choosing an R substituent of the pyridine capable of solubilising the molecule in that solvent. For example the molecules described herein may be soluble in common organic solvents such as dichloromethane and chloroform.

The molecules described herein may be solution processable. For example, devices comprising the molecules described herein may be fabricated by solution processing techniques such as electrodeposition, spin coating, drop casting, dip coating, doctor blading, spray coating, ink-jet printing, Langmuir-Blodgett, nanoimprint lithography, microcontact printing, and/or roll-to-roll printing techniques such as gravure printing, offset printing and/or flexographic printing. Forming thin films of the molecules from solution is a desirable alternative to vacuum deposition. Although vacuum deposition is a widely used technique to form thin films of material for numerous applications, it is expensive and therefore solution processing is a viable, less expensive alternative.

The molecules described herein may present a neutral pH. The molecules may not be acidic. The molecules may present non-acidic and/or pH neutral functionalities. Advantageously, the performance of devices fabricated with the molecules described herein may be superior to the performance of devices fabricated with other currently used acidic materials, such as PEDOT:PSS, due to the lack of acidic functionalities in the structure of the molecules. Acidity of a layer, such as the hole injection layer, hole transport layer and/or electrode layer, can deteriorate other layers in the device, leading to contamination and decrease in device performance.

The molecules described herein may be precursors to a conductive material. The molecules described herein may form a conductive material in solution. For example, solubilised molecules described herein may be doped in solution to form a conductive material. The doped conductive material may be a doped dimer of the molecules described herein. A doped dimer of the molecules described herein may be a conductive material. A film of the conductive material described herein may be deposited from solution.

The conductive material described herein may be formed by doping the molecules described herein in solution. The conductivity of the conductive material may be raised, for example by several orders of magnitude, by chemical or electrochemical doping. P- doping involves oxidation of the molecules and/or conductive material and n-doping involves reduction of the molecules and/or conductive material. Doping the molecules and/or conductive material described herein may involve the partial oxidation or reduction of the molecules and/or conductive material, each oxidation state exhibiting its own characteristic reduction potential. The molecules and/or the conductive material described herein may be chemically doped in solution with a dopant. Suitable dopants may comprise, but are not limited to NOBF₄, NOPF₆, NOSbF₆, FeCI₃, F₄TCNQ, AsF₅, DDQ, nitrosonium salts, chloranil, TNF and TCNE. The molecules and/or the conductive material described herein may be electrochemically doped in solution.

According to a second aspect there is provided a transparent conductive film or coating. The film may be obtainable by preparing a solution through dissolving a molecule described herein or a functionally active derivative thereof in a solvent, forming a conductive material by doping the solution for example with a suitable dopant and depositing a film of conductive material from the solution.

Solvents suitable for dissolving a molecule described herein may comprise, but are not limited to methanol, ethanol, acetone, acetonitrile, chloroform, dichloromethane, carbon tetrachloride, chlorobenzene, cyclohexane, diethyl ether, ethyl acetate, hexane, toluene, dimethyl sulfoxide (DMSO), tetrahydrofuran and water.

Doping the solution may comprise electrochemically doping the solution or chemically doping the solution. Chemically doping the solution may comprise of adding a dopant selected from the group comprising of NOPF₆, NOSbF₆, F₄TCNQ, AsF₅, DDQ, nitrosonium salts, chloranil, TNF and TCNE. For example, chemically doping the solution may comprise adding nitrosonium salts, NOPF₆ or NOSbF₆. Chemical dopants may be added to the solution in any suitable concentration. For example, chemically doping the solution may comprise adding chemical dopants to the solution in a range of about 0.5 to about 10 molar equivalents. Chemically doping the solution may comprise adding chemical dopants to the solution in a range of about 1 to about 5 molar equivalents. Chemically doping the solution may compise adding 2.5 molar equivalents of a chemical dopant, such as nitrosonium salts, NOPF₆ or NOSbF₆ to the solution.

Depositing a film of conductive material from the solution may be performed by any suitable solution processing technique. Suitable solution processing techniques may comprise, but are not limited to electrodeposition, spin coating, drop casting, dip coating, doctor blading, spray coating, ink-jet printing, Langmuir-Blodgett, nanoimprint lithography, microcontact printing, and/or roll-to-roll printing techniques such as gravure printing, offset printing and/or flexographic printing. In one embodiment the film of conductive material is made by drop casting. A film described herein may present controllable levels of doping while controlling the degree of transparency and film morphology. The concentration of dopant in a film of the conductive material described herein may be modified to tune the conductivity of the film. Changing the doping levels in a film of the conductive material may affect the transmittance of the film and the film morphology. The transmittance and morphology of the film may be optimised for each concentration of dopant in the film, for example by drop casting the film, adding solvent additives and the like. For example, films of the molecules and/or conductive material described herein may present a doping level of 2.5 molar equivalents of NOPF₆ or NOSbF₆. Controlled levels of doping are crucial for ensuring successful conductivity of the layer. Layers and/or films of the molecules and/or conductive material of the present invention may present reproducible controlled levels of doping that can be adjusted depending on the application, while maintaining a smooth and uniform morphology.

A film of the conductive material described herein may present a transmittance comparable to ITO and PEDOT:PSS in the UV-Vis light spectral region. Films of the conductive material described herein may present transmittance of up to 90% at 100 nm thickness in the visible light spectral region. Films of the conductive material described herein may present transmittance in the region of 30%-90% in the UV-Vis light spectral region. For example, films of the conductive material described herein may present transmittance up to 60% in the UV-Vis light spectral region.

A film of the conductive material described herein may present a conductivity between 4.0 x 10^~7 and 1 S/cm after doping. A film of the conductive material described herein may present conductivity of up to 1000 S/cm after doping. The conductivity of films of the conductive material described herein may be optimised, for example by using different dopants and/or dopant concentrations.

A film of the conductive material described herein may be used as a conductive layer in an organic electronic device. A film of the conductive material described herein may be used as a transparent conductive standalone electrode in an organic electronic device. A film of the conductive material described herein may be used as a charge transport layer in an organic electronic device. A film of the conductive material described herein may be used as a hole injection layer in an organic electronic device. For example, a film of the conductive material described herein may be used as a transparent electrode and/or interlayer electrode in organic photovoltaics (OPVs) (also known as organic solar cells), organic light emitting diodes (OLEDs), and the like. For example, a film of the conductive material described herein may have applications in display technologies, solar light harvesting, mobile and computer devices and/or lighting applications. In a third aspect there is provided a method of tuning the properties of the molecules described herein, the method comprising altering the substituents of the molecules. Altering the substituents may comprise of chemically modifying one or more of the R, XrX₄ and/or Y substituents of the molecule. Altering the substituents may comprise choosing substituents tailored to the desired application. For example, R substituents may be chosen to provide solubility in different solvents and/or to provide the required molecular packing to achieve a smooth film morphology. As such, the solubility of the molecules can be tailored to the solvent required for each specific application. XrX₄ and/or Y substituents may be chosen to alter the bandgap of the molecule. As such, the bandgap of the molecules can be tailored to the required application. For example, the HOMO and/or LUMO energy levels of the molecules may be tuned to match the HOMO and/or LUMO levels of adjacent functional layers and/or electrodes.

In a fourth aspect there is provided a transparent conductive coating comprising a film of a transparent conductive material described herein.

In a fifth aspect there is provided a transparent standalone electrode comprising a film of a conductive material described herein.

In a sixth aspect there is provided an organic electronic device comprising a film of a conductive material described herein. In one embodiment, the organic electronic device may be a thin film organic electronic device. For example, thin film organic electronic devices may be prepared by depositing a film of the conductive transparent material described herein on a transparent substrate, such as ITO or glass, and depositing electrodes on the film. In one embodiment the conductive transparent material is deposited by a drop casting technique known in the art and described herein. In one embodiment, the organic electronic device may be an organic photovoltaic (OPV). In another embodiment, the organic electronic device may be an organic light emitting diode OLED. In yet another embodiment, the organic electronic device may be an electrochromic device. For example, electrochromic devices may be prepared by using a transparent standalone electrode of the fifth aspect as a working electrode to electrochemically deposit an electrochromic material on the electrode.

Brief description of the Figures The present invention will now be further described by way of example and with reference to the figures which show:

Figure 1 shows a top view of a thin film device comprising a film described herein, the device is used for electrical, surface and thickness measurements.

Figure 2 shows current-voltage (IV) characteristics for thin film devices fabricated using the following compounds: (a) 4b, (b) 4a, (c) 4f, (d) 4h, (e) 4i and (f) 4k.

Figure 3 shows AFM images for the surface of the most conductive thin film devices containing the following compounds: (a) 4b, (b) 4a, (c) 4f, (d) 4h, (e) 4i and (f) 4k.

Figure 4 shows a view of the light beam (green dotted line) on the substrate in UV/Vis spectrophotometer. Figure 5 shows the transmittance of thin films taken at different points in the film and the subsequent average value.

Figure 6 shows current-voltage (IV) characteristics for thin film devices fabricated using compound 4r with dopants (a) NOPF₆ and (b) NOSbF₆

Figure 7 shows AFM surface images of compound 4r films cast from solutions doped with (a) NOSbF₆ and (b) NOPF₆.

Figure 8 shows the transmittance of thin films of compound 4r doped with NOPF₆ (1 ) and NOSbF₆ (2) taken at different points in the film and the subsequent average value.

Figure 9 shows an example of current voltage (IV) characteristics from film of 4r doped with NOSbF₆

Figure 10 shows example of current voltage (IV) characteristics from film of compound 4 doped with NOSbF₆ Figure 1 1 shows Current density-voltage-luminance characteristics of OLEDs fabricated using Poly[2-methoxy-5-(2-ethylhexyloxy)-1 ,4-phenylenevinylene] (MEH- PPV) emissive layer and with device architectures (a) ITO/HTL 1/MEH-PPV/Ca/AI; (b) ITO/HTL 2/MEH-PPV/Ca/AI; (c) ITO/HTL 3/MEH-PPV/Ca/AI; (d) ITO/HTL 4/MEH- PPV/Ca/AI; (e) ITO/HTL 5/MEH-PPV/Ca/AI; (f) ITO/HTL 6/MEH-PPV/Ca/AI

Figure 12 shows Current density-voltage-luminance characteristics of OLED with device architecture ITO/HTL 3/Green 2/Ca/AI

Detailed description of the Invention

A series of molecules were synthesised with general structure

where Xi-X₄ is H, Y is H, R are different solubilising chains and A^" is Br^" . The compounds are small molecules with a bis-EDOT coupled to a pyridine with different solubilising moieties at the 1 -position of the pyridine. The molecules are soluble in common organic solvents including but not limited to chloroform, toluene, acetonitrile, chlorobenzene, dimethyl sulfoxide, ethylene glycol, dichloromethane and tetrahydrofuran. These small molecules are conductive, transparent and soluble in common solvents, but they do not comprise any acidic functionalities. This is advantageous since acidity can be detrimental for device performance and longevity as adjacent layers of the device can be damaged in an acidic environment.

The experimental conditions for the synthesis of a series of molecules described herein are presented below. General synthetic scheme

Compound 2 - BisEDOT

3,4-Ethylenedioxythiophene (10.0 g, 7.51 ml, 70.35 mmol, 1 .0 equiv.) was dissolved in anhydrous THF (150 ml) and cooled to -80 °C, where n-butyllithium (freshly titrated at 2.29 M in hexanes, 21 .95 ml, 73.16 mmol, 1 .04 equiv.) was added slowly. On complete addition, the reaction mixture was warmed to 0 °C in an ice/salt bath and stirred for 2 h under Ar. After this time, copper(ii) chloride (10.03 g, 74.57 mmol, 1 .06 equiv.) was added, causing a colour change (colourless to black) and an exotherm (approx. 35 °C). The reaction mixture was then stirred under Ar for 40 h. After this time, the mixture was poured into crushed ice in water (600 ml), then stirred for 45 mins, before being extracted with dichloromethane (2 ^χ 300 ml). The dichloromethane layer was filtered through a plug of Celite (dimensions, h: 8 cm, w: 5 cm) with further washing with dichloromethane (1200 ml). The solvent was removed under vacuum, and the resulting light brown solid suspended in hexane and stirred for 24 h. The product was then isolated by filtration with drying under vacuum affording the product, compound 2, as a tan coloured powder (6.02 g, 61 %); m.p. 197-199 °C (dec); ¾ (CDCI₃, 400.13 MHz) 6.29 (2H, s, ArH), 4.36-4.34 (4H, m, CH₂), 4.27-4.25 (4H, m, CH₂); <5_C (CDCI₃, 100.61 MHz) 141 .2, 97.5, 65.0, 64.6.²

Compound 3 - 2-(Tributylstannyl)bisEDOT

BisEDOT (4.5 g, 15.94 mmol, 1.0 equiv.) was dissolved in anhydrous THF (85 ml) and cooled to -30 °C, where n-butyllithioum (2.29 M in hexanes, 6.96 ml, 15.94 mmol, 1 .0 equiv.) was added dropwise. On complete addition, the reaction mixture was stirred at - 30 °C for 10 min, then warmed to 0 °C and stirred for a further 1 h. After this time, the reaction mixture was treated with tri-n-butyltin chloride (4.54 ml, 16.74 mmol, 1 .05 equiv.) and stirred under Ar for 48 h. After this time, the reaction mixture was quenched by addition of water (200 ml) and brine (50 ml), then extracted with dichloromethane (150 ml, then 2 ^χ 100 ml). The organic layers were combined, dried over MgS0₄ then filtered. Evaporation of the solvent afforded the product, compound 3, as a dark brown oil, that was dried under vacuum for 24 h and used in the next step without further purification (7.17 g, 79%, as judged by ¹ H NMR); <5_H (CDCI₃, 400.13 MHz) 6.25 (1 H, s, ArH), 4.38-4.29 (4H, m, CH₂), 4.25-4.18 (4H, m, CH₂), 1 .64-1 .53 (6H, m, CH₂), 1 .39- 1.30 (6H, m, CH₂), 1 .19-1 .14 (6H, m, CH₂), 0.94-0.85 (9H, m, CH₃).

Compound 4 - BisEDOT-Pyridine

² G. A. Sotzing, J. R. Reynolds, P. J. Steel, Adv. Mater. 1997, 9, 726.

4-Bromopyridine hydrochloride (3.66 g, 18.82 mmol, 1.5 equiv.) was added to a 100 ml conical flask and dissolved in distilled water (50 ml). To this, and equimolar solution of potassium carbonate (2.60 g, 18.82 mmol, 1 .5 equiv. in 50 ml of distilled water) was added, and the aqueous solution extracted with diethyl ether (3 ^χ 30 ml). The organic extracts were combined, dried (MgS0₄), filtered and concentrated to a slightly pink oil, which was then re-dissolved in anhydrous toluene (40 ml). Meanwhile, compound 3 (7.17 g, 12.55 mmol, 1 .0 equiv.) and tetrakis(triphenylphosphine) palladium(O) (1.45 g, 1 .26 mmol, 0.1 equiv.) were charged to a reaction flask, evacuated and purged with Ar (x 3). Anhydrous toluene (80 ml) was added and the mixture stirred for 15 min before addition of the solution of 4-bromopyridine in toluene. The resulting dark brown mixture was heated to reflux for 48 h under Ar. After this time, the mixture was cooled to room temperature and quenched by addition of water (500 ml) and brine (100 ml), before being extracted with ethyl acetate (3 ^χ 200 ml). The combined organic layers were washed with brine (250 ml), dried over MgS0₄, filtered and concentrated under vacuum to a light orange gum. Purification on silica gel column chromatography, eluting with 7:3 ethyl acetate/dichloromethane, afforded the product as a light orange powder. Further purification was achieved by dissolving this powder in the minimum volume of hot dichloromethane (approx. 50 ml) and further reducing this volume through heating. Once the volume of solvent had been reduced to 20 ml, the solution was cooled to room temperature and ice cold hexane (100 ml) added. The resulting precipitate was isolated by filtration and dried under vacuum, before compound 4 was isolated as a light yellow powder (2.54 g, 54%); m.p. 190 °C (dec); <5_H (CDCI₃, 400.13 MHz) 8.52 (2H, d, J = 6.4 Hz, ArH), 7.60 (2H, d, J = 6.4 Hz, ArH), 6.36 (1 H, s, ArH), 4.42-4.39 (6H, m, CH₂), 4.29-4.27 (2H, m, CH₂); <5_C (CDCI₃, 100.61 MHz) 149.9, 141 .3, 140.7, 140.4, 137.9, 137.3, 128.5, 1 19.4, 1 1 1 .5, 1 1 1 .3, 109.4, 99.0, 65.2, 64.9, 64.7, 64.6; m/z (MALDI-TOF) 359.0; HRMS: found [M]⁺, 359.0283; C₁₇H₁₃N0₄S2 requires [M]⁺, 359.0281 .

Alternative synthetic route to Compound 4

Scheme 1. Alternative synthesis of compound 4 by direct arylation

4-lodopyridine (0.1 09 g, 0.531 mmol) was dissolved in anhydrous DMF (7 ml) before 2,2\3,3'-tetrahydro-5,5'-bithieno[3,4-b][1 ,4]dioxine (0.2 g, 0.708 mmol), potassium acetate (0.209 g, 2.125 mmol) and Pd(OAc)₂ (0.012 g, 0.053 mmol) were added and the reaction heated to 80 °C under nitrogen overnight. After cooling to room temperature, the reaction mixture was poured into water (50 ml), stirred for 20 mins then filtered and washed with water (2 χ 50 ml). The residual solids were digested with ethyl acetate (3 χ 50 ml), combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. Purification was achieved using column chromatography (ethyl acetate) to give 4-(2,2',3,3'-tetrahydro-[5,5'-bithieno[3,4-b][1 ,4]dioxin]-7-yl)pyridine (94 mg, 37%) as a yellow solid (mp. 190 °C, dec). ¹ H NMR (CDCI₃, 400 MHz) δ 8.52 (2H, d, J = 6.4 Hz, ArH), 7.60 (2H, d, J = 6.4 Hz, ArH), 6.36 (1 H, s, ArH), 4.42-4.39 (6H, m, CH₂), 4.29-4.27 (2H, m, CH₂); ¹³C NMR (CDCI₃, 100 MHz) δ 149.9, 141 .3, 140.7, 140.4, 137.9, 1 37.3, 128.5, 1 19.4, 1 1 1 .5, 1 1 1 .3, 109.4, 99.0, 65.2, 64.9, 64.7, 64.6; LRMS (El, m/z) 359.3.

Representative general procedure for formation of alkylated BisEDOT-Pyridine derivatives

Compound 4 (100-400 mg, 1 .0 equiv.) was suspended in acetonitrile (anhydrous, 30- 100 ml, approx. 25-30 ml per 100 mg of compound 4) and heated to reflux. During heating, alkyl halide (1 .0 ml per 100 mg of compound 4) was added and, once at reflux, the mixture was continued at reflux for 72 h. After this time, the mixture was cooled to room temperature and concentrated to low volume (approx. 5-10 ml). Ice cold diethyl ether (100 ml per 100 mg of compound 4) was added, causing a red precipitate to form, which was then filtered, washed with further diethyl ether (100 ml per 100 mg of compound 4), dried and isolated as dark red powder. Compound 4a

Compound 4a, 217 mg (99%); m.p. 130-132 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.02 (2H, d, J = 6.8 Hz, ArH), 7.99 (2H, d, J = 6.0 Hz, ArH), 6.52 (1 H, s, ArH), 4.72 (2H, t, J = 7.2 Hz, CH₂), 4.55-4.45 (6H, m, CH₂), 4.33-4.31 (2H, m, CH₂), 2.03-1 .97 (2H, m, CH₂), 1 .41 -1 .27 (6H, m, CH₂), 0.89 (3H, t, J = 6.8 Hz, CH₃); <5_C (CDCI₃, 100.61 MHz) 142.8, 1 19.9, 101 .9, 65.2, 65.0, 64.0, 59.6, 31.1 , 30.7, 25.2, 21 .9, 13.4; m/z (MALDI- TOF) 443.92; HRMS: found [M-Br]⁺, 444.1287; C₂₃H₂₆N0₄S₂ requires [M-Br]⁺, 444.1298.

Compound 4b

Compound 4b, 141 mg (92%); m.p. 121 -124 °C (dec); <5_H (DMSO-d⁶, 400.13 MHz) 8.55 (2H, d, J = 7.2 Hz, ArH), 8.09 (2H, d, J = 7.2 Hz, ArH), 6.89 (1 H, s, ArH), 4.59- 4.57 (2H, m, CH₂), 4.51-4.50 (2H, m, CH₂), 4.44-4.40 (4H, m, CH₂), 4.31-4.30 (2H, m, CH₂), 1.88-1.82 (2H, m, CH₂), 1.29-1.24 (10H, m, CH₂), 0.88-0.85 (3H, m, CH₃); <5_C (DMSO-d⁶, 100.61 MHz) 147.0, 146.3, 144.1, 141.7, 140.3, 137.8, 120.8, 118.0, 108.1, 107.9, 102.8, 66.3, 66.1, 65.2, 64.8, 59.6, 31.6, 31.0, 28.9, 28.8, 25.9, 22.5, 14.4; m/z (MALDI-TOF) 472.00; HRMS: found [M-Br]⁺, 472.1603; C₂₅H₃oN0₄S₂ requires [M-Br]⁺, 472.1611.

Compound 4c

Compound 4c, 240 mg (98%); m.p.110-112 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.03 (2H, d, J= 6.6 Hz, ArH), 7.98 (2H, d, J= 6.6 Hz, ArH), 6.51 (1H, s, ArH), 4.71 (2H, t, J = 7.2 Hz, CH₂), 4.54-4.44 (6H, m, CH₂), 4.32-4.30 (2H, m, CH₂), 2.01-1.97 (2H, m, CH₂), 1.35-1.25 (18H, m, CH₂), 0.91-0.87 (3H, m, CH₃); <5_C (CDCI₃, 100.61 MHz) 147.1, 145.4, 142.9, 140.9, 119.9, 101.9, 65.2, 65.0, 64.0, 59.7, 31.4, 31.2, 29.1, 29.0, 28.9, 28.8, 28.6, 25.6, 22.2, 13.6; m/z (MALDI-TOF) 527.93; HRMS: found [M-Br]⁺, 528.2243; C₂9H₃₈N0₄S₂ requires [M-Br]⁺, 528.2237.

Compound 4d

Compound 4d, 271 mg (98%); m.p.128-130 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.02 (2H, d, J= 7.2 Hz, ArH), 7.94 (2H, d, J= 6.8 Hz, ArH), 6.47 (1H, s, ArH), 4.68 (2H, t, J = 7.2 Hz, CH₂), 4.52-4.43 (6H, m, CH₂), 4.30-4.28 (2H, m, CH₂), 1.97-1.94 (2H, m, CH₂), 1.32-1.21 (26H, m, CH₂), 0.88-0.85 (3H, m, CH₃); <5_C (CDCI₃, 100.61 MHz) 147.7, 146.1, 143.5, 141.5, 140.3, 137.3, 120.6, 120.3, 108.8, 108.4, 102.6, 65.9, 65.6, 64.7, 60.2, 32.1, 31.9, 29.9, 29.83, 29.79, 29.7, 29.6, 29.5, 29.3, 26.3, 22.9, 14.3; m/z (MALDI-TOF) 584.44; HRMS: found [M-Br]⁺, 584.2874; C₃₃H4₆N0₄S₂ requires [M-Br]⁺, 584.2863. Compound 4f

Compound 4f, 112 mg (81%); m.p.163-165 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.02 (2H, d, J= 7.2 Hz, ArH), 7.98 (2H, d, J= 6.4 Hz, ArH), 6.50 (1H, s, ArH), 4.72 (2H, t, J =7.4 Hz, CH₂), 4.53-4.43 (6H, m, CH₂), 4.31-4.29 (2H, m, CH₂), 1.98 (2H, t, J= 7.4 Hz, CH₂), 1.47-1.41 (2H, m, CH₂), 0.98 (3H, t, J = 7.4 Hz, CH₃); <5_C (CDCI₃, 100.61 MHz) 147.8, 146.1, 143.5, 137.4, 120.6, 65.9, 65.7, 64.7, 60.0, 33.7, 19.6, 13.8; m/z (MALDI- TOF) 416.19; HRMS: found [M-Br]⁺, 416.0980; C₂₁H₂₂N0₄S₂ requires [M-Br]⁺, 416.0985. Compound 4q

Compound 4g, 191 mg (98%); m.p.112-114 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.00 (2H, d, J= 6.8 Hz, ArH), 7.98 (2H, d, J= 6.0 Hz, ArH), 6.50 (1H, s, ArH), 4.70 (2H, t, J = 7.0 Hz, CH₂), 4.52-4.44 (6H, m, CH₂), 4.31-4.29 (2H, m, CH₂), 1.99-1.97 (2H, m, CH₂), 1.41-1.19 (14H, m, CH₂), 0.87 (3H, t, J= 6.8 Hz, CH₃); <5_C (CDCI₃, 100.61 MHz) 147.7, 146.1, 143.6, 141.6, 140.4, 137.3, 120.6, 108.9, 108.4, 102.6, 65.9, 65.7, 64.7, 60.3, 32.0, 31 .9, 29.64, 29.57, 29.4, 29.3, 26.3, 22.8, 14.3; m/z (MALDI-TOF) 500.33; HRMS: found [M-Br]⁺, 500.1935; C27H34NO4S2 requires [M-Br]⁺, 500.1924.

Compound 4h

Compound 4h, 131 mg (92%); m.p. 94-95 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.00 (2H, d, J = 8.0 Hz, ArH), 7.99 (2H, d, J = 8.0 Hz, ArH), 6.51 (1 H, s, ArH), 4.71 (2H, t, J = 8.0 Hz, CH₂), 4.53-4.44 (6H, m, CH₂), 4.31 -4.29 (2H, m, CH₂), 2.00 (2H, t, J = 8.0 Hz, CH₂), 1 .39-1 .28 (4H, m, CH₂), 0.90 (3H, t, J = 8.0 Hz, CH₃); <5_C (CDCI₃, 100.61 MHz) 147.7, 146.1 , 143.6, 141 .6, 140.4, 137.3, 120.6, 120.4, 108.4, 102.6, 65.9, 65.7, 64.8, 60.3, 31.6, 28.3, 22.4, 14.1 ; m/z (MALDI-TOF) 430.20; HRMS: found [M-Br]⁺, 430.1 131 ; C22H25NO4S2 requires [M-Br]⁺, 430.1 141 .

Compound 4i

Compound 4i, 143 mg (95%); m.p. 92-93 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.00 (2H, d, J = 7.2 Hz, ArH), 7.99 (2H, d, J = 7.2 Hz, ArH), 6.51 (1 H, s, ArH), 4.70 (2H, t, J = 7.4 Hz, CH₂), 4.53-4.44 (6H, m, CH₂), 4.31 -4.29 (2H, m, CH₂), 2.03-1.95 (2H, m, CH₂), 1 .41 -1 .23 (8H, m, CH₂), 0.87 (3H, t, J = 7.2 Hz, CH₃); <5_C (CDCI₃, 100.61 MHz) 147.7, 146.1 , 143.5, 141 .6, 140.4, 137.3, 120.6, 120.4, 108.4, 102.6, 65.9, 65.7, 64.7, 60.3, 31 .9, 31 .7, 29.0, 26.2, 22.7, 14.2; m/z (MALDI-TOF) 458.24; HRMS: found [M-Br]⁺, 458.1441 ; C₂4 H2₈N0₄S2 requires [M-Br]⁺, 458.1454.

Compound 4i

Compound 4j, 151 mg (96%); m.p. 1 14-1 15 °C (dec); <5_H (CDCI₃, 400.13 MHz) 8.99 (2H, d, J = 8.0 Hz, ArH), 8.00 (2H, d, J = 8.0 Hz, ArH), 6.52 (1 H, s, ArH), 4.71 (2H, t, J = 8.0 Hz, CH₂), 4.53-4.45 (6H, m, CH₂), 4.32-4.30 (2H, m, CH₂), 2.02-1 .97 (2H, m, CH₂), 1 .39-1 .25 (12H, m, CH₂), 0.87 (3H, t, J = 7.0 Hz, CH₃); <5_C (CDCI₃, 100.61 MHz) 147.7, 146.1 , 143.5, 141 .6, 137.3, 120.6, 102.6, 65.9, 65.7, 64.8, 60.3, 32.0, 31.9, 29.5, 29.3, 26.3, 22.8, 14.3; m/z (MALDI-TOF) 486.27; HRMS: found [M-Br]⁺, 486.1755; C₂₆H3₂N0₄S₂ requires [M-Br]⁺, 486.1767.

Compound 4k

Compound 4k, 131 mg (95%); m.p. 169-170 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.01 (2H, d, J = 8.0 Hz, ArH), 8.00 (2H, d, J = 8.0 Hz, ArH), 6.52 (1 H, s, ArH), 4.69 (2H, t, J = 8.0 Hz, CH₂), 4.54-4.45 (6H, m, CH₂), 4.32-4.30 (2H, m, CH₂), 2.10-2.04 (2H, m, CH₂), 1 .05 (3H, t, J = 8.0 Hz, CH₃); <5_C (CDCI₃, 100.61 MHz) 143.6, 120.6, 102.6, 65.9, 65.7, 64.8, 61.5, 25.2, 10.8; m/z (MALDI-TOF) 402.05; HRMS: found [M-Br]⁺, 402.0820; C₂oH₂₀N0₄S₂ requires [M-Br]⁺, 402.0828.

Compound 4m

Compound 4m, 124 mg (87%); m.p. 224-225 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.00 (2H, d, J = 8.0 Hz, ArH), 8.00 (2H, d, J = 8.0 Hz, ArH), 6.52 (1 H, s, ArH), 4.72 (2H, t, J = 8.0 Hz, CH₂), 4.54-4.45 (6H, m, CH₂), 4.32-4.30 (2H, m, CH₂), 1 .92-1 .87 (2H, m, CH₂), 1 .74-1 .71 (1 H, m, CH), 1.02 (6H, d, J = 8.0 Hz, 2 ^χ CH₃); <5_C (CDCI₃, 100.61 MHz) 147.7, 146.1 , 143.5, 120.7, 108.9, 108.4, 102.6, 65.9, 65.7, 64.7, 58.8, 40.6, 25.8, 22.6; m/z (MALDI-TOF) 430.08; HRMS: found [M-Br]⁺, 430.1 131 ; C₂₂H₂₄N0₄S₂ requires [M-Br]⁺, 430.1 141 .

Compound 4n

Compound 4n, 161 mg (99%); m.p. 88-90 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.15 (2H, d, J = 8.0 Hz, ArH), 7.96 (2H, d, J = 8.0 Hz, ArH), 6.52 (1 H, s, ArH), 4.98 (2H, t, J = 4.0 Hz, CH₂), 4.53-4.44 (6H, m, CH₂), 4.32-4.30 (2H, m, CH₂), 4.04 (2H, t, J = 4.0 Hz, CH₂), 3.68-3.65 (2H, m, CH₂), 3.62-3.59 (4H, m, CH₂), 3.56-3.54 (2H, m, CH₂), 3.40 (3H, s, CH₃); <5_C (CDCI₃, 100.61 MHz) 148.0, 146.1 , 144.2, 137.4, 120.3, 102.6, 72.1 , 70.6, 70.4, 70.0, 65.9, 65.6, 64.7, 59.4, 59.2; m/z (MALDI-TOF) 506.1 ; HRMS: found [M-Br]⁺, 506.1314; C₂₄H₂₈N0₇S₂ requires [M-Br]⁺, 506.1302.

Compound 4p

Compound 4p, 139 mg (95%); m.p. 141 -143 °C (dec); <5_H (CDCI₃, 400.13 MHz) 9.00 (2H, d, J = 8.0 Hz, ArH), 7.99 (2H, d, J = 8.0 Hz, ArH), 6.51 (1 H, s, ArH), 4.71 (2H, t, J = 8.0 Hz, CH₂), 4.53-4.44 (6H, m, CH₂), 4.31 -4.29 (2H, m, CH₂), 2.03-1 .95 (2H, m, CH₂), 1 .62-1 .58 (1 H, m, CH), 1 .29-1 .24 (2H, m, CH₂), 0.89 (6H, d, J = 8.0 Hz, 2 ^χ CH₃); <5_C (CDCI₃, 100.61 MHz) 147.7, 146.1 , 143.6, 141.6, 140.4, 137.3, 120.6, 108.9, 108.4, 102.6, 65.9, 65.7, 64.7, 60.4, 35.1 , 29.8, 27.9, 22.6; m/z (MALDI-TOF) 444.09; HRMS: found [M-Br]⁺, 444.1288; C₂₃H₂₆N0₄S₂ requires [M-Br]⁺, 444.1298.

Compound 4q³

Compound 4q, 146 mg (100%); m.p. 225-227 °C (dec); <5_H (CDCI₃, 400.13 MHz) 8.89 (2H, d, J = 8.0 Hz, ArH), 8.02 (2H, d, J = 8.0 Hz, ArH), 6.53 (1 H, s, ArH), 4.74 (2H, q, J = 8.0, CH₂), 4.58-4.52 (2H, m, CH₂), 4.48-4.45 (4H, m, CH₂) 4.32-4.30 (2H, m, CH₂), 1 .69 (3H, t, J = 8.0 Hz, CH); <5_C (DMSO-d⁶, 100.61 MHz) 146.5, 145.8, 143.4, 141 .2, 139.8, 137.3, 120.4, 1 17.4, 107.6, 107.3, 102.3, 65.8, 65.6, 64.7, 64.3, 54.6, 16.1 ; m/z (MALDI-TOF) 388.12; HRMS: found [M-l]⁺, 388.0670; C₁₉H₁₈IN0₄S₂ requires [M-l]⁺, 388.0672.

Compound 4r

³ Note that the reaction temperature was 60 °C to avoid loss of 1 -iodoethane during the extended reaction time. Synthesised using procedure A. Compound 4r, 140 mg (95%); m.p. 215-216 °C (dec); <5_H (DMSO-d⁶, 400.13 MHz) 8.67 (2H, d, J = 8.0 Hz, ArH), 8.1 1 (2H, d, J = 8.0 Hz, ArH), 6.88 (1 H, s, ArH), 5.23-5.20 (1 H, m, OH), 4.60-4.58 (2H, m, CH₂), 4.52-4.43 (6H, m, CH₂) 4.31 -4.29 (2H, m, CH₂), 3.84-3.80 (2H, m, CH₂); <5_C (DMSO-d⁶, 100.61 MHz) 146.6, 145.8, 144.1 , 141 .2, 139.8, 137.4, 120.1 , 107.6, 107.3, 102.3, 65.8, 65.6, 64.7, 64.3, 61 .5, 60.1 ; m/z (MALDI-TOF) 404.08; HRMS: found [M-l]⁺, 404.0609; C₁₉H₁₈IN0₅S₂ requires [M-l]⁺, 404.0621 .

Film preparation and characterisation

Spin coated films

A solution of NOPF₆ (2.5 eq) in anhydrous acetonitrile (0.5 ml) was added to a solution of one of the molecules 4a, 4b, 4f, 4h, 4i or 4k, (10 mg) in anhydrous chloroform (0.5 ml) and the mixture was left to stir overnight at room temperature.

Glass substrates were cleaned using deionised water, acetone and propan-2-ol with ultra-sonication and dried over a stream of compressed air before being subject to UV- ozone treatment for 2 minutes.

A layout of the structure of the thin films used for conductivity testing is shown in Figure 1 .

The previously prepared solution comprising one of the molecules 4a, 4b, 4f, 4h, 4i or 4k, was used to spin-coat the glass substrates at a spin speed of 2000 rpm and the coated substrates were annealed at ^~\ 00°C for 20 minutes. After annealing the substrates, the sides of the substrates were cleaned to reveal glass to improve metal contacts. The substrates were placed in a sample holder with shadow mask for the deposition four pairs of Al electrodes (dimensions: 1 .5 mm ^χ 4 mm). The holder and mask were placed in the evaporation chamber and 70 nm thick Al electrodes were deposited at 1 ^χ 10^~6 mbar. Once the chamber had returned to atmospheric pressure, the substrates were removed and conductive silver paint was applied to the outside edges of the electrodes to improve the contacts and the paint was allowed to dry for 20 minutes. Drop casted films

Example 1 :

Compound 4r (0.8 mg, 1 eq) in anhydrous acetonitrile (0.1 ml) was added to NOSbF₆ (1 .0 mg, 2.5 eq) in anhydrous acetonitrile (0.1 ml) before dilution with DMSO (0.8 ml). A glass substrate was coated using 4 drops of the solution and left to dry for 16 hours. The sides of the substrates were cleaned to reveal glass to improve metal contacts. The substrates were placed in a sample holder with shadow mask for the deposition four pairs of Al electrodes (dimensions: 1 .5 mm ^χ 4 mm). The holder and mask were placed in the evaporation chamber and 70 nm thick Al electrodes were deposited at 1 ^χ 10^~6 mbar. Once the chamber had returned to atmospheric pressure, the substrates were removed and conductive silver paint was applied to the outside edges of the electrodes to improve the contacts and the paint was allowed to dry for 20 minutes. An IV sweep was recorded for each set of electrodes and the conductivity was calculated as stated above. Example 2:

Compound 4r (0.8 mg, 1 eq) in anhydrous acetonitrile (0.1 ml) was added to NOPF₆ (0.7 mg, 2.5 eq) in anhydrous acetonitrile (0.1 ml) before dilution with DMSO (0.8 ml). A glass substrate was coated using 4 drops of the solution and left to dry for 16 hours. The sides of the substrates were cleaned to reveal glass to improve metal contacts. The substrates were placed in a sample holder with shadow mask for the deposition four pairs of Al electrodes (dimensions: 1 .5 mm ^χ 4 mm). The holder and mask were placed in the evaporation chamber and 70 nm thick Al electrodes were deposited at 1 ^χ 10^~6 mbar. Once the chamber had returned to atmospheric pressure, the substrates were removed and conductive silver paint was applied to the outside edges of the electrodes to improve the contacts and the paint was allowed to dry for 20 minutes. An IV sweep was recorded for each set of electrodes and the conductivity was calculated as stated above.

Conductivity measurements

An IV sweep was recorded for each set of electrodes. The resistance of the films was determined using the inverse of the gradient and the conductivity was then calculated using the following equations: where, p = resistivity, R = resistance, A = cross section area of film and I = distance between electrodes. And:

1

σ = -

P where, σ = conductivity.

A schematic diagram of devices fabricated with the molecules described herein is shown in Figure 1 . Thin film devices comprising a film of the conductive material described herein were prepared on glass substrates of 15 x 15 mm. The red bar shows the active device area where the resistivities were measured.

Figure 2 shows current-voltage (IV) plots for each film tested. The inverse of the gradient is used to calculate resistance (R = V/l). The resistivity (p) is then calculated using this value and the inverse of the resistivity is the conductivity (σ).

Table 1- Conductivity measurements on devices fabricated with molecules described herein spin coated from solution.

Average Highest Surface Film

Compound Standard

Conductivity Conductivity roughness Thickness number Deviation

(S cm^"1) (S cm^"1) (nm) (nm)

1 .80 x 1 0^"

4b 2.84 x 1 0^"7 4.9 x 1 0^"7 7 96 574

4a 0.01 4 0.01 7 0.0031 44 297

4f 0.01 9 0.024 0.0030 38 21 2

4h 0.01 8 0.028 0.01 2 25 282 4i 2.6 x 10^"a 3.6 x 10^"J 8.8 x 10^"4 33 333

4k 6.4 x 10^"a 7.0 x 10^"a 6.6 x 10^"4 35 322

Table 1 shows the results of conductivity measurements performed on devices fabricated with molecules described herein and data on theRSM roughness (which is an indication of the uniformity of the film) of the films shown in Figure 3.

The root mean square roughness (RRMS) is calculated using the following equation:

Where n = no. of values and yi = height of ith point - average height. In general, lower the surface roughness of the films leads to more uniform films, which are more suitable for use as a hole-injection layer. A rough surface will cause materials deposited on top of the hole-injection layer to also have a rough surface, which is generally detrimental to performance.

Surface analysis was recorded by atomic force microscopy (AFM) using tapping mode on various locations on the surface of the thin film devices prepared as shown in Figure 1 . In addition, thickness measurements were performed in 10 different areas of the sample. To avoid ambiguity in measurements, the surface roughness and thicknesses were measured on the devices used in electrical measurements. AFM images of the surface of films of the most conductive devices are shown in Figure 3 and AFM images of the surface of drop casted solutions of molecule 4r with two different dopants are shown in Figure 6.

UV-Vis transmission spectroscopy was performed on samples using a standard UV-Vis spectrometer. Since the measurement is limited by the shape and dimensions of the light spot, transmission spectra were recorded in the middle of the samples, away from the location of the top electrodes. Samples processed with same conditions as above were used to measure transmission on locations of the film other than the top electrodes. The areas where the spectra are recorded are divided by the black dotted line shown in Figure 4 into the left, centre and right regions which are used to characterise transmittance across the film.

Figure 5 shows the % transmittance of light at the wavelength of highest absorption ( max)- There are three values which have been combined to give an average to ensure the whole surface is taken into consideration. The higher the value for transmittance, the more suitable for the material is for a role in a device. Low transmittance means light will be absorbed from emission of an OLED device (i.e., self-absorption) or from the incident light on an OPV device, reducing OLED brightness or light intensity reaching the OPV active layer, respectively. As shown in Figure 5, transmittances of over 50 % were obtained with some of the molecules tested.

The experimental results are comparable to experimental data obtained from devices prepared as described above with commercially available PEDOT:PSS (Heraeus, Clevios™ P VP AL 4083), the conductivity of which was measured to be 0.005 S cm^"1 with a RMS roughness of 1 nm, thickness of 65 nm and a transmittance of 83% at the wavelength of maximum absorbance. The conductivity achieved with some of the molecules described herein was up to four times greater than that of PEDOT:PSS and although the transmittance was somewhat lower than that of PEDOT:PSS, this can be attributed to the thickness and roughness of the films, which has to be experimentally optimised. In particular, the thickness of films of the molecules described herein has to be optimised without compromising conductivity in order to improve transparency of the films. Table 2 shows data of conductivity measurements performed on drop-casted films of compound 4r doped with NOSbF₆ and with NOPF₆ and as well as thickness and roughness data obtained on those films (see also Figure 6). AFM images of those films are presented on Figure 7.

Table 2- Conductivity measurements and film roughness and thickness measurements for films drop-casted from doped molecule 4r solutions

Dopant Average Highest Standard Surface Film conductivity conductivity roughness Thickness (S cm ¹) (S cm ¹) deviation (nm) (nm)

NOSbF₆ 0.48 1 .03 0.36 2.8 180

NOPF₆ 0.31 0.48 0.17 1 1 .9 143

Films comprising compound 4r chemically doped with NOSbF₆ present higher conductivity and lower surface roughness than films of compound 4r chemically doped with NOPF₆, the films having similar thickness. Additionally, films comprising of compound 4r chemically doped with NOSbF₆ exhibited transmittances of greater than 75% (see figure 8).

Compared to the results shown on Table 1 for spin coated films of other materials of the family, thinner films of compound 4r present comparatively greater conductivities and lower surface roughness. The increased conductivity is likely due to the greater uniformity of the drop-cast films.

Conductivity - Compound 4r Spin-coated Films

NOSbF₆ (12.6 mg, 2.5 eq) in anhydrous acetonitrile (0.5 ml) was added to Compound 4r (10 mg, 1 eq) in anhydrous acetonitrile (0.5 ml) before being left to stir for 16 hours. The ITO substrate was coated by spin-coating at 2000 rpm and the film was annealed at 120 °C for 20 minutes. The sides of the substrates were cleaned to reveal glass to improve metal contacts. The substrates were placed in a sample holder with shadow mask for the deposition four pairs of Al electrodes (dimensions: 1 .5 mm ^χ 4 mm). The holder and mask were placed in the evaporation chamber and 70 nm thick Al electrodes were deposited at 1 ^χ 10^~6 mbar. Once the chamber had returned to atmospheric pressure, the substrates were removed and conductive silver paint was applied to the outside edges of the electrodes to improve the contacts and the paint was allowed to dry for 20 minutes. An IV sweep was recorded for each set of electrodes and the conductivity was calculated as stated above. See Figure 9 and Table 3.

Table 3. Conductivity results from doped 4r films

Compound Average Maximum Standard Film Thickness conductivity (S conductivity (S deviation (nm)

aData averaged over22 devices

Conductivity - Compound 4 Drop Cast Films

NOSbF₆ (1 .4 mg, 2.5 eq) in anhydrous acetonitrile (0.1 ml) was added to a solution of compound 4 (0.8 mg, 1 eq) in anhydrous acetonitrile (0.1 ml). The solution was diluted with anhydrous DMSO (0.8 ml). A glass substrate was coated using 4 drops of the solution and left to dry for 16 hours. The sides of the substrates were cleaned to reveal glass to improve metal contacts. The substrates were placed in a sample holder with shadow mask for the deposition four pairs of Al electrodes (dimensions: 1 .5 mm χ 4 mm). The holder and mask were placed in the evaporation chamber and 70 nm thick Al electrodes were deposited at 1 χ 10^"6 mbar. Once the chamber had returned to atmospheric pressure, the substrates were removed and conductive silver paint was applied to the outside edges of the electrodes to improve the contacts and the paint was allowed to dry for 20 minutes. An IV sweep was recorded for each set of electrodes and the conductivity was calculated as stated above. See Figure 10 and Table 4.

Table 4. Conductivity results from doped compound 4 films

aData averaged over 65 devices OLED Fabrication

Indium tin oxide (ITO) was washed using deionised water, acetone and isopropanol with ultra-sonication before being dried over compressed air and treated with UV-ozone for 2 minutes. Various hole transport layers were then deposited using the following conditions:

HTL 1 :

NOPF₆ (0.7 mg, 2.5 eq) in anhydrous acetonitrile (0.1 ml) was added to Compound 4r (0.8 mg, 1 eq) in anhydrous acetonitrile (0.1 ml) before dilution with anhydrous DMSO (0.8 ml). The ITO substrate was coated using 4 drops of the solution and left to dry for 16 hours. HTL 2:

NOPF₆ (8.2 mg, 2.5 eq) in anhydrous acetonitrile (0.5 ml) was added to Compound 4r (10 mg, 1 eq) in anhydrous acetonitrile (0.5 ml) before being left to stir for 16 hours. The ITO substrate was coated by spin-coating at 2000 rpm and the film was annealed at 120 °C for 20 minutes.

HTL 3:

NOPF₆ (8.2 mg, 2.5 eq) in anhydrous acetonitrile (0.45 ml) was added to Compound 4r (10 mg, 1 eq) in anhydrous acetonitrile (0.45 ml) before dilution with anhydrous DMSO (0.1 ml). The solution was then left to stir for 16 hours. The ITO substrate was coated by spin-coating at 2000 rpm and the film was annealed at 120 °C for 20 minutes.

HTL 4:

NOSbF₆ (1 .0 mg, 2.5 eq) in anhydrous acetonitrile (0.1 ml) was added to Compound 4r (0.8 mg, 1 eq) in anhydrous acetonitrile (0.1 ml) before dilution with DMSO (0.8 ml). The ITO substrate was coated using 4 drops of the solution and left to dry for 16 hours HTL 5:

NOSbF₆ (12.6 mg, 2.5 eq) in anhydrous acetonitrile (0.5 ml) was added to Compound 4r (10 mg, 1 eq) in anhydrous acetonitrile (0.5 ml) before being left to stir for 16 hours. The ITO substrate was coated by spin-coating at 2000 rpm and the film was annealed at 120 °C for 20 minutes.

HTL 6:

NOSbF₆ (12.6 mg, 2.5 eq) in anhydrous acetonitrile (0.45 ml) was added to Compound 4r (10 mg, 1 eq) in anhydrous acetonitrile (0.45 ml) before dilution with anhydrous DMSO (0.1 ml). The solution was then left to stir for 16 hours. The ITO substrate was coated by spin-coating at 2000 rpm and the film was annealed at 120 °C for 20 minutes.

Following HTL deposition, MEH-PPV (concentration: 4 mg ml^"1 in toluene) was deposited by spin-coating the solution at 800 rpm. The film was then annealed at 80 °C for 20 minutes. Calcium (40 nm) and aluminium (40 nm) electrodes were deposited by thermal evaporation at 1 ^χ 10^~6 mbar and active area of 4 mm ^χ 1 .5 mm was obtained by using a shadow mask. Current-Voltage-Luminance data was measured in the glovebox in a light-tight box. See Figure 1 1 and Table 5.

Table 5. OLED performance of devices containing HTLs based on compound 4r

HTL Turn on Voltage at Maximum Current Efficiency 10 Cd m ² (V) Luminance (Cd m^"2) (Cd A^"1)

1 4.95 751 @ 14.55 V 0.23 @ 7.2 V

2 4.2 616 @ 14.55 V 0.23 @ 4.2 V

3 6 552 @ 12.9 V 0.24 @ 10.95 V

4 5.25 1504 @ 12.75 V 0.26 @ 12.3 V

5 5.4 499 @ 10.05 V 0.04 @ 9.75 V

6 5.55 771 @ 10.35 V 0.08 @ 10.2 V

Further OLED Fabrication

Indium tin oxide (ITO) was washed using deionised water, acetone and isopropanol with ultra-sonication before being dried over compressed air and treated with UV-ozone for 2 minutes. HTL 3 had previously been prepared by dissolving compound 4r (10 mg, 1 eq) in anhydrous acetonitrile (0.5 ml) and NOPF₆ (8.2 mg, 2.5 eq) in a separate vial with anhydrous acetonitrile (0.5 ml. The NOPF6 solution was added to 4r solution and the resulting solution was stirred overnight. The solution was deposited onto the ITO substrate by spin-coating at 2000 rpm for 60 seconds before annealing at 100 °C for 20 minutes. Compound Green 2 was deposited according to a previous procedure (J. Mater. Chem. C. 2016 4 3774-3780). Calcium (40 nm) and aluminium (40 nm) electrodes were deposited by thermal evaporation at 1 ^χ 10^~6 mbar and active area of 4 mm x 1 .5 mm was obtained by using a shadow mask. Current-Voltage-Luminance data was measured in the glovebox in a light-tight box. See Figure 12 and Table 6.

Table 6. OLED results using HTL solution 3 with Green 2 emissive layer (J. Mater. Chem. C. 2016 4 3774-3780)

HTL Turn on Voltage at Maximum Current Efficiency

10 Cd m^"2 (V) Luminance (Cd m^"2) (Cd A^"1)

3 4.95 751 @ 14.55 V 0.23 @ 7.2 V

Claims

CLAIMS: olecule for use as a conductive coating, the molecule having the structure:

wherein R is present or absent and when present is selected from the group comprising an alkyl chain, an oligoether chain, an aliphatic alcohol and/or an amine functionality;

XrX₄ is selected from the group comprising H, an electron-donating group and/or an electron-withdrawing group;

Y is selected from the group comprising H, an electron-donating carbocyclic aromatic ring, an electron-donating aromatic heterocycle, an electron-withdrawing aromatic carbocyclic ring and/or an electron withdrawing aromatic heterocycle; and

A^" is present when R is present and is any suitable counterion, such as F^", CI^" Br^", I^", PF₆ ^", BF₄ ^", SbF₆ ^", TsO^", or MsO^".

2- The molecule of claim 1 , wherein the molecule comprises pH neutral or substantially neutral functionalities.

3- The molecule of claim 1 or 2, wherein the electron-donating group is selected from the group comprising

-NR₂ . -NH₂ ,— OH ,— OR . — NH

4- The molecule of any one of claims claim 1 to 3, wherein the electron-withdrawing group is selected from the group comprising

o O O O O O O

-N-0 -NR, -NH, -S- OH — C≡N — CF₃ —CCI —COH —COR — CR — CH

O

5- The molecule of claim 1 or 2, wherein XrX₄ is H, Y is H, A^" is Br^" or and R is selected from the group comprising a linear alkyi chain, a branched alkyi chain, a linear oligoether, a branched oligoether, an alcohol, an amine, a linear alkyi chain functionalised with an hydroxyl functionality, a branched alkyi chain functionalised with a hydroxyl functionality, a linear alkyi chain functionalised with an amine functionality, a branched alkyi chain functionalised with an amine functionality and/or combinations thereof.

6. The molecule of claim 1 or 2 wherein XrX₄ is H, Y is H and A and R are absent.

7- The molecule of any preceding claim, wherein the molecule is monodisperse.

8- The molecule of any preceding claim, wherein the physical, chemical and/or electrical properties of the molecule are modified by chemical functionalisation of the molecule.

9- The molecule of any preceding claim, wherein physical, chemical and/or electrical properties the molecules are modifiable by a physical processing technique selected from the group comprising solvent treatment, solvent vapour annealing, thermal annealing, plasma pre-treatment of the substrate, encapsulation, deposition method, and/or molecular self-assembly.

10- The molecule of any preceding claim, wherein the molecule is soluble in common organic solvents.

11 - The molecule of any one of claims 1 to 8, wherein the molecule is soluble in water- miscible solvents.

12- A film obtainable by: preparing a solution by dissolving a molecule according to any one of claims 1 to 1 1 in a solvent; forming a conductive material by doping the solution; depositing a film of conductive material from the solution.

13- The film of claim 1 1 , wherein doping the solution comprises: electrochemically doping the solution; or chemically doping the solution by adding a dopant selected from the group comprising to NOPF₆, NOSbF₆, F₄TCNQ, AsF₅, DDQ, nitrosonium salts, chloranil, TNF and TCNE.

14- The film of claims 12 or 13, wherein the film presents transmittance of up to 90 % at 100 nm film thickness in the UV-Vis spectral region, such as between 300-800nm.

15- The film of any one of claims 12 to 14, wherein the film presents a conductivity of up to 1000 S/cm.

16- The film of any one of claims 12 to 15, wherein the film is used as a conductive layer in an organic electronic device.

17- The film of claim 16, wherein the film is used as a transparent conductive standalone electrode in the organic electronic device.

18- The film of any one of claims 12 to 17, wherein the film has applications in display technologies, solar light harvesting, mobile and computer devices and/or lighting applications.

19. The film of any one of claims 12 to 18 wherein the film has been made by a drop casting technique.

20- A method of tuning the properties of the molecule of any one of claims 1 to 1 1 , the method comprising altering one or more of the Xi-X₄, Y and/or R substituents of the molecule.

21 - A transparent electrode comprising a film according to any one of claims 12 to 1 19.

22- An organic electronic device comprising a film according to any one of claims 12 to 19.