WO2020034022A1 - Synthesis of a fluorophore-class compound, compound produced and use thereof, process for producing white organic light emitting diodes and diodes produced - Google Patents

Abstract

The present invention relates to the synthesis of a class of fluorophores developed by combining the salicylidene and benzazole classes, and to the compound produced and the technical use thereof in the form of a light emitting diode (WOLED). Said synthesis produces a compound which has advantageous optical and electronic properties and high potential for use in light emitting diodes. The present invention further relates to a process for producing white organic light emitting diodes (WOLEDs) as well as to the diodes produced.

Description

 SYNTHESIS OF A COMPOUND OF THE FLUOROPHORE CLASS, COMPOUND OBTAINED AND ITS USE, PROCESS OF OBTAINING ORGANIC DIODES

 WHITE LIGHT EMITTERS AND DATA OBTAINED

 Field of the invention:

 [001] The present invention falls within the field of application of chemistry and electricity, more specifically in the area of solid state devices using organic materials as an active part specially adapted for light emission, since it refers to an unprecedented synthesis of a class of fluorophores developed by combining the classes of salicylidenes and benzazoles, as well as the obtained compound and its technological application in the form of white light emitting diode (White Organic Light Emitting Diode - WOLED).

 Basics of the invention:

 [002] Physico-chemical dynamics resulting from the absorption of radiation in the ultraviolet and visible (UV / Vis) regions by molecular systems are objects of study in many areas of science. The development of such systems has numerous applications, including the design of optoelectronic devices, chemical or material sensors and imaging.

[003] The intramolecular proton transfer reaction in the excited state (ESIPT) has great relevance in the field of materials science with the development of fluorescent probes and photonic devices. This is a common reaction in aromatic systems with atoms that promote intramolecular hydrogen bonding. With the transfer of the proton, a tautomeric balance is generated between two species in the state electronic excited. In this context, the solvent has its importance in the stabilization of the species present in the excited state, influencing the lifetime of N *. In protic polar solvent (methanol, ethanol, etc.) there may be a strong interaction of N with the medium, generating competition with the intermolecular proton transfer.

 [004] Experimentally, the occurrence of ESIPT can be identified by the emission of light in steady state. In high polarity media, the intramolecular hydrogen bond prevents T * from forming and only the N * band is expected. In solution, this property is well described in the literature, containing several examples in the use of these molecules as probes to measure the polarity of the medium.

 [005] In this sense, the generation of ESIPT in solid state, specifically through electrical processes (Electrically Generated Intramolecular Proton Transfer - EGIPT) becomes relevant and allows the design of devices emitting white light. The first description for this purpose is from 1996 and since then the use of this phototautomeric balance for the manufacture of prototypes has been the focus of research, whether through the physical mixture of components, by the synthesis of compounds with more than one site reactive to ESIPT or even by using a single molecule with a single reactive site.

[006] Among the reactive systems to ESIPT are benzazolic derivatives, molecules made up of a five-membered heterocycle fused to an aromatic six-carbon ring. This one has two heteroatoms: the first is a nitrogen atom and the other can be a sulfur atom oxygen or nitrogen. Benzazolic derivatives constitute an extremely versatile class of compounds that perform ESIPT. Concomitantly, there is the class of salicylidenes, Schiff bases produced by the condensation of hydroxy-aldehydes or a-hydroxy-carboxylic acids and aromatic diamines.

 [007] As an alternative to the generation of white light on dials, the present invention proposes the unprecedented synthesis of a class of fluorophores developed by the combination of these two classes of compounds, specifically as a form of proof of concept by the use of a system derived from benzothiazole , as well as its technological application in the form of light emitting diode: the N, N '-bis (salicylidene) - (2- (3', 4 '- diaminophenyl) benzothiazole (BTS).

 [008] For this purpose, devices were manufactured using the spin-coating methodology, which has the BTS dispersed in poly (iV-vinylcarbazole) (PVK) and poly semiconductors as an active layer [9, 9 - dioctylfluorenyl-2,7-diyl] (PFO). In both cases, WOLEDs were developed with good efficiency, which match the systems reported in the literature and with good technological appeal, since the deposition of active layers by spin-coating represents energy savings when compared to the thermal evaporation method, a important step in the search for sustainability.

 [009] In the state of the art there are some documents that describe several compounds with optical properties to be used as an active layer in WOLEDs.

[010] US2004001970A describes a series of compounds derived from Schiff's Bases used in subsequent synthesis of coordination compounds, which were used as an active layer in WOLEDs, thus suggesting more operational steps from the point of view of preparing the active layer. In addition, these coordination compounds are part of devices produced by thermal evaporation of their constituent layers, differing from the present invention, which uses centrifugal deposition technology (spin-coating) from the active layer, thus distancing itself in the area of semiconductor polymers for the manufacture of organic / polymeric light-emitting diodes. Differently and advantageously, in addition to saving materials for the production of a device emitting white light, the present invention proposes a more sustainable system because it is not necessary to use potentially toxic metals, only organic compounds. With a single molecule as an active layer and its doping in PVK, it was possible to obtain white light (which in general is obtained by combining more than one material) using the electrical conduction properties liable to semiconductor polymers. Subsequently, the same device architecture had its electrical properties improved by the use of the PFO polymer, in which case it took advantage of its electro-emission of blue color to complement the final white color.

[011] The documents W02004005280, CN102395647A and US20120046472A1 also refer to compounds that have an intramolecular proton transfer characteristic in the excited state (ESIPT). However, the proposed diodes have the active layer evaporated and use more carrier and blocking layers, thus promoting a high energy expenditure. In contrast, in addition to proposing an unprecedented compound with differentiated optical and electronic properties, the present invention proposes to obtain diodes with less spent materials to achieve white emission, more sustainable by using solution processing methods and, unexpectedly, proposes the reduction of energy consumption and infrastructure for the assembly of diodes.

 [012] However, the document US2015031067A, despite being a derivative of salicylidene and benzazole, said compound does not have the same optical properties of the present invention, especially because it does not have white emission. It is another compound, with a distinct synthetic route, which was used to detect ions in solution, distancing itself from the purpose proposed for the BTS compound. These compounds resemble BTS in that they are also reactive to ESIPT. However, the reactive site involves another functional group, thus promoting a fluorescence emission that covers the entire region of the visible in the electromagnetic spectrum.

[013] Therefore, the main innovation is in the product of the synthesis and its application as an active layer in light emitting diodes based on semiconductor polymers. It is an unprecedented compound with differentiated optical and electronic properties and with great potential for application. Its application as an active layer is highlighted because it has an emission spectrum covering practically the entire region of the visible due to a chemical reaction that occurs when the system is subjected to an electrical potential, a fact of extreme relevance for the production of WOLEDs. Thus, the use of its electroemission can occur in different ways varied depending on the color you want to obtain: it can be deposited as a single active layer and optimized its proportion or by mixing with other active layers, which allows the use of energy transfer processes as an alternative to improve performance. Furthermore, the architecture of the devices described in the present invention is also a differential (diodes based on semiconductor polymers) as it also opens up the possibility of producing flexible substrates / displays.

 [014] Therefore, no state-of-the-art document describes the synthesis of a class of fluorophores developed by combining the classes of salicylidenes and benzazoles, as well as the technological application in the form of a light-emitting diode of the compound obtained N, N'-bis (salicylidene) - (2- (3,4-diaminophenyl) benzothiazole (BTS), as proposed by the present invention.

 Brief description of the invention:

 [015] The present invention relates to a synthetic route of a class of fluorophores developed by combining the classes of salicylidenes and benzazoles, as well as the compound obtained and its technological application in the form of WOLED.

[016] Said synthetic route comprises the steps of a) adding 0.2 mmol of 2- (3 ', 4'-diaminophenyl) benzothiazole and 0.4 mmol of salicylic aldehyde in ethanolic medium; b) heat the mixture to reflux, at the boiling temperature of the solvent, preferably at 78 ° C, for 24 hours, in order to guarantee total conversion of the reagents into product; and c) filter, wash and recrystallize the mixture. [017] In this way the compound N, N'-bis (salicylidene) - (2- (3 ', 4' -diaminophenyl) benzothiazole (BTS) is obtained in the form of an orange solid in 90% yield, the which has different optical and electronic properties and with great potential for application in light emitting diodes.

 [018] Thus, in addition, the present invention relates to a process of obtaining organic white light emitting diodes (WOLEDs) by the methodology of solution processing (spin-coating) through the deposition of at least one active layer of dispersed BTS in the semiconductor polymers poly (N-vinylcarbazole) (PVK) and poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO), as well as the diodes obtained.

 Brief description of the figures:

 [019] To obtain a total and complete visualization of the object of this invention, the figures to which reference is made are presented, as follows.

 [020] Figure 1 is a schematic of the synthesis of the database

Schiff BTS, in which compound (a) was obtained commercially,

(b) is the result of the basic hydrolysis of (a), (c) is the product of the condensation of aminothiophenol (reduction of (b) with the use of PBu3) with 3,4-diaminobenzoic acid, and the Schiff base called "BTS" is the result of the condensation reaction between

(c) and salicylic aldehyde.

 [021] Figure 2 is the result of a spectrum

BTS's Vibrational.

 [022] Figure 3 is the result of a spectrum of

BTS 1H Magnetic Resonance.

[023] Figure 4 shows a spatial arrangement of the BTS structure in its crystalline form using the Monocrystal X-Ray Diffraction technique.

[024] Figure 5 shows graphically the standardized electronic spectrum of emission (PL - At _exc = 335 nm, 420 nm, 460 nm) and excitation (PLE - obtained from the maximums of PL) in DMSO in which the absorption spectrum was inserted (dot plot) to assist in visualizing the PLE spectrum, and the BTS concentration was 8.5 x 10 ⁶ mol L ^_1 .

[025] Figure 6 shows graphically the standardized electronic spectra of absorption (plot in points), PL and PLE for BTS in pyridine with the variation of excitation. Concentration: 8.5 x 10 ⁶ mol L ^_1 .

 [026] Figure 7 shows graphically the electroluminescence spectra of WOLEDs made using PVK (left) and PFO (right).

 Detailed description of the invention:

 [027] The present invention relates to a synthetic route of a class of fluorophores developed by combining the classes of salicylidenes and benzazoles, as well as the compound obtained.

 [028] In more detail, this summary comprises the steps of:

 a) Add 0.2 mmol of 2- (3 ', 4'-diaminophenyl) benzothiazole and 0.4 mmol of salicylic aldehyde in ethanolic medium;

 b) Heat the mixture to reflux; and

 c) Filter, wash and recrystallize the mixture.

[029] In step "a", the mixing of said compounds is carried out in a suitable container for heating. In the implementation, without, however, restricting for this modality, a round-bottomed flask of a mouth coupled to a condenser was used as a suitable container for heating.

 [030] It is worth noting that, in order to exemplify the invention, the synthesis was performed in suitable containers, such as beakers, volumetric flasks, conical flasks, falcon tubes and beakers. However, it is worth noting that the present invention is not limited by the said examples, and other containers for reproduction on an industrial scale can be used.

 [031] Still in step "a", the reaction is preferably carried out in 15 ml of ethanol.

 [032] In step "b", the mixture is preferably heated to reflux, at the boiling temperature of the solvent, preferably at 78 ° C, for 24 hours, in order to guarantee total conversion of the reagents into product.

 [033] At the end of the period, in step "c" the desired product precipitates in the reaction medium, which is filtered, washed with ethanol and recrystallized using ethanol / tetrahydrofuran (EtOH / THF). More specifically, the precipitate is vacuum filtered and washed with cold ethanol. Subsequently, the compound is dissolved in ethanol / tetrahydrofuran under heating, so that the mixture comes to a boil and the whole product solubilizes. Thereafter, the ambient temperature (approximately 25 ° C) is reached naturally to form the crystals.

 [034] At the end, the product is obtained as an orange solid with 90% yield and melting point 224-

226 C certifying its purity. Said compound presents the chemical structure (1) and nomenclature N, N'- bis (salicylidene) - (2- (3 ', 4-diaminophenyl) benzothiazole), abbreviated by BTS.

[035] For a better understanding, Figure 1 presents a schematic of the synthesis of the Schiff BTS base, in which compound (a) was obtained commercially, (b) is the result of the basic hydrolysis of (a), (c) is the condensation product of aminothiophenol (reduction of (b) using PBu3) with 3,4-diaminobenzoic acid, and the Schiff base called "BTS" is the result of the condensation reaction between (c) and salicylic aldehyde.

[036] To better define the characterization of said compound, BTS comprises ¹ H NMR (500 MHz, DMSO-d6, õ = ppm) 6.52-6.59 ppm (m, 2H), 6.73-6.80 ppm (d, 2H, J = 8.5Hz), 7.25-7.32 ppm (t, 2H, J = 7Hz), 7.42-7.56 ppm (dd, 2H, J = 7Hz), 7.47-7.62 ppm (dt, 2H, J = 7.5 Hz), 8.06 ppm (s, 2H), 8.09-8.18 ppm (dd, 2H, J = 8Hz), 8.49 ppm (s, 1H), 9.06 ppm (s, 1H) and 9.15 ppm (s, 1H). Infrared (cm-1): 3058 (V CHarom), 1609-1592 (VC = N), 755 (V CS).

[037] Through electronic absorption and emission spectroscopies, it was possible to demonstrate that the system is in its protonated (N) and deprotonated (A) forms in the ground state. The high reactivity of the system in terms of photoreaction of proton transfer in the excited state (ESIPT) and the tautomeric balance formed in the excited state (N * T *).

 [038] Additionally, the present invention relates to the use of the BTS compound for application in light emitting diodes.

 [039] For this, BTS can be applied as an active layer in optoelectronic devices. Its application as an active layer is highlighted for having an emission spectrum covering practically the entire region of the visible, a fact of extreme relevance for the production of white emission devices (WOLEDs). Thus, the use of its electro-emission can occur in different ways depending on the color you want to obtain: you can deposit the system as a single active layer and optimize its proportion or by mixing it with other active layers, which allows the use of energy transfer as an alternative to improve performance. In addition, it can also be used to form complexes with transition metals or as an analyte for quantifying metal ions in solution.

[040] To prove that said compound can be used in light emitting diodes, the devices were manufactured using the spin-coating methodology, which has the BTS dispersed in poly (iV semiconductor polymers) as an active layer. -vinylcarbazole) (PVK) and poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO). In both cases, organic diodes emitting white light (White Organic Light Emitting Diodes - WOLEDs) were developed with good efficiency, which are equivalent to the systems reported in the literature and with good technological appeal, since the deposition of active layers by spin-coating represent energy savings when compared to the thermal evaporation method, an important step in the search for sustainability.

 [041] Thus, the process of obtaining WOLEDs comprises the steps of:

a) Wash the ITO substrates (25 W crrr ² ) in an ultrasound bath with a mixture of solvents;

 b) Deposit at least one layer of poly (3, 4-ethylenedioxythiophene) -poly (styrenesulfonate) (PEDOT: PSS) by spin-coating;

c) Deposit at least one layer of thickness 60 to 85 nm of the physical mixtures PVK: BTS and PF0: BTS (0.5%, 1.0% and 2.5% mol / mol) from a solution in tetrahydrofuran ( 2.6 x 10 ² mol L ^_1 ) under an inert atmosphere;

 d) Evaporate a thick layer of metallic calcium and aluminum by thermal evaporation.

 [042] In step "a", said mixture of solvents comprises the solvents selected from the group consisting of deionized water, isopropyl alcohol, neutral detergent and acetone, in which more specifically the washing is carried out in stages being first in a mixture of distilled water and neutral detergent (50% / 50% v / v), followed by acetone and later isopropyl alcohol.

 [043] In step "b", on the substrates, a layer, preferably 30 nm thick, of poly (3,4-ethylenedioxythiophene) -poly (styrenesulfonate) is deposited

(PED0T: PSS) by spin-coating. For this purpose, the following parameters are preferably used: 5000 rpm of agitation, for 60 seconds, in which annealing is carried out for at least 30 min at 110 ° C. [044] In step "c", alternatively, the PFO devices must immediately comprise an extra layer of PVK (2.6 x 10 ² mol / L) on the ITO, deposited at, preferably, 3000 rpm for 60s. Still in step "c", the inert atmosphere chamber must be adjusted to the lowest possible conditions, for example [H ₂ 0] <1 ppm and [Cg] <40 ppm.

 [045] In step "d", a layer of metallic calcium (30 nm) and aluminum (100 nm) is preferably evaporated by thermal evaporation with the aid of an evaporation chamber, such as mBraun Evaporator.

 [046] Thus, through the proposed process, WOLED devices are obtained, which comprise:

 - glass covered with tin doped indium oxide (ITO) and polystyrene poly (3,4-ethylenedioxythiophene) sulfonate (PEDOT: PSS);

- from 0.5 to 2.5% PVK: BTS, preferably 2.6 x 10 ² mol / L; and

- from 0.5% to 2.5% PFO: BTS, preferably 2.6 x 10 ² mol / L.

 [047] In a preferred embodiment of the present invention, the said WOLEDs obtained are:

 glass | ITO | PEDOT: PSS | PVK: BTS (0.5%, 1.0% and 2.5 mol / mol%) | Ca | Al; and

 - glass | ITO | PEDOT: PSS | PVK | PFO: BTS (0.5%, 1.0% and 2.5% mol / mol) | Ca | THERE .

[048] The layers of ITO and metallic aluminum act as anode and cathode, respectively. PEDOT polymer: PSS acts as a hole injector, PVK as an electron blocker and hole carrier, PFO acts as hole conveyor and metallic calcium layer aids in cargo mobility.

 [049] The optical and electrical properties of WOLEDs were obtained after encapsulating the devices with an epoxy resin.

 [050] Furthermore, the architecture of the referred WOLEDs of the present invention also allows the production of flexible substrates / displays, if the substrate used is, alternatively to the glass substrate covered by ITO, a flexible material substrate.

 [051] To prove the potential of the WOLEDS proposed here below, examples of the invention and tests performed are presented.

 Tests

 -_Synthesis_do_N, N '-bis (sali cilidene) - (2- (3', 4 '- diaminophenyl) benzothiazole) [BTS]:

 [052] In a 25 mL flask, 15 mL of ethanol, 50.0 mg (0.2 mmol) of 2- (3 ', 4'-diaminophenyl) benzothiazole and 44.2 pL (50.6 mg, 1,146 g cm-3, 0.4 were added mmol) of salicylic aldehyde. This mixture was heated to reflux for 24h. At the end of the period, the flask had its mixture filtered, the filtered precipitate was washed with ethanol and recrystallized by the two solvent method in Ethanol / Tetrahydrofuran (EtOH / THF). At the end, the product was obtained as an orange solid with 90% yield.

 - Monocrystal X-Ray Diffraction:

[053] To obtain the sample crystals, a recrystallization procedure was carried out using the two solvent method: 30 mg of BTS were added in 20 mL of hot ethanol, together with tetrahydrofuran (THF) added drop by drop until the sample is completely solubilized. The final mixture was left to stand at room temperature (approximately 25 ° C) allowing the slow formation of precipitate in the form of needle crystals. The structure of the BTS compound was solved using the single crystal X-ray diffraction technique by the APEX2 equipment from Bruker®. The data were processed using the software SAINT, SHELXS97 and SHELXL2014 / 7, also of the Bruker® brand, for refinement and resolution of the structure.

[054] Regarding the infrared (IV) spectrum, it was expected to observe the presence of stretches of phenolic hydroxyls, but due to the formation of intramolecular hydrogen (LH) bonding, this signal, in the region of 3700-3300 crrr ¹ , was not observed. The infrared spectrum (Figure 2) presents as strains of the imine group (C = N) that occurs between 1609 crrr ¹ and 1592 cm ^-1 as the main band for BTS characterization.

 [055] In the proton NMR spectrum (Figures 3A-B), the first set of interesting signals to prove the structure of the synthesized system would be the phenolic hydroxyl singlet, again they do not appear in the spectrum due to the presence of intramolecular LH. The second set of relevant signals refers to the imine group, the hydrogens referring to the -N = CH- bonds are found in the expected region at 9.06 ppm and 9.15 ppm - there are two types of signals for these protons because the system does not it is symmetrical.

[056] Finally, the last analysis carried out to characterize the BTS ligand was that of monocrystal X-ray diffraction. At this point, the molecule was recrystallized by the two-solvent method using ethanol and THF. It is The analysis offered the parameters of the unit cell of the compound, which belongs to the point group P21 / c of the monoclinic system. Figure 4 presents in a graph with the atoms of this structure in the form of ellipsoids and their spatial disposition when crystalline, it can be seen that one of the phenol rings that originate the salicylidene function is outside the plane.

 - Photophysical Characterization:

 [057] The steady state absorption, emission and excitation spectra were collected using Hewlett Packard® model 8452 A equipment and the ISS® model PCI photon counting spectrofluorimeter. The compound was dissolved in stock solutions of dimethyl sulfoxide (DMSO) to a final concentration of 1.0 x 10

³ mol Lr ¹ and dissolved to a final concentration of 3.0 x 10 ⁶ mol Lr ¹ to 1.5 x 10 ⁵ mol Lr ¹ to obtain the absorption spectra and 8.5 x 10 ⁶ mol Lr ¹ for the emission / excitation spectra. The quantum fluorescence yield was determined relative to that of the standard quinine sulfate in 0.5 mol Lu ¹ sulfuric acid, with the standard at the concentration of 8.5 x 10 ⁶ mol L ^_1 , by equation 1 below:

F _{j S} p nj

 F FR (D

where Fi and F _p represent the integrated areas of the sample and standard emissions, £; e and _n the absorption coefficients, 7i; ² en _v ² the refractive indices of the solvents of each system (sample and standard) and <p _p is the quantum yield of the standard.

[058] All analyzes were performed in a cuvette quartz with 1.0 cm optical path.

 [059] For the characterization of the emission profile of the molecule, it was defined how the system behaves in the excited state. Excitation at different wavelengths and obtaining excitation spectra (PLE) based on emission maximums (PL) allowed us to assess which species (s) are found in the fundamental and excited states (Figure 5).

[060] For the BTS issue, one species was expected to be in the ground state and two in the excited state, as a consequence of the occurrence of the phototautomeric balance between the N * and T * forms - the Stokes Shift value greater than 6000 crrr ¹ for the band around 490 nm indicates this. However, from the PL and PLE spectra shown in Figure 6, the presence of two distinct species in equilibrium in the ground state and three in the excited state is evident. In other words, there is a third species to be attributed, which is also in the fundamental state. In this sense, the strategy chosen to solve this problem was to carry out the same photophysical study in pyridine, as shown in Figure 6.

[061] Pyridine is a highly basic solvent, this means that in pyridine the BTS will be in its deprotonated form. When PL is taken at 335 nm it is possible to verify the residual presence of the protonated form, with a maximum of around 370 nm, a value close to that found for protonated form of the binder in the other solvents. And this is the species present in other situations (Figure 5) in both the fundamental and excited states, appearing as a third band in the emission spectrum with maximum approximately 530 nm.

 [062] Therefore, the BTS molecule in solution is found in the ground state in the protonated (N) and deprotonated (A) forms, and in the excited state it is reactive to the process of intramolecular proton transfer (ESIPT) producing the T * tautomer, which deactivates radiatively and, when in the fundamental state (T), undergoes recombination originating the form N (intramolecular transfer of protons in the fundamental state, from the English "Ground State Intramolecular Proton Transfer - GSIPT).

 [063] Still with respect to the spectrum of Figure 5, the dependence on the solvent contradicts the expected trend with the increase in polarity. The T * form has its spectrum shifted to blue with the increase in the polarity of the medium, which again highlights the importance of intramolecular LH for stabilization of the excited state. The two other species, N * and A *, have their spectra shifting to red by increasing the forces of solute-solvent interaction with the creation of intermolecular LH, more intense for the A * form because it is an anion.

 - Electroluminescence of WOLEDs:

[064] Voltage current curves were measured with the Keithley SourceMeter 2400 electrometer. The electroluminescence spectra were acquired using the Ocean Optics USB2000 + bench spectrometer. In addition, voltage luminance curves and chromaticity coordinates were obtained, following the 1931 definition of the International Lighting Commission (CIE 1931), using the Konica Minolta CS-100A luminancimeter and a No. lens. 110, ø = 40.5 mm. [065] The first set of BTS WOLEDs in PVK resulted in the generation of white light for all fractions used (0.5%, 1.0% and 2.5% mol / mol), with very close CIE 1931 coordinates: (0.29,0.36), (0.31,0.40) and (0.33,0.39), respectively. The doping of 1.0% was the one that offered the best results, with luminance and current density 34 cd m-2, 0.46 A cm-2 and CIE at (0.31; 0.40) when used 13, 5V . This device has a better performance than that obtained by Jenekhe et al in 1996. At the time, a semiconductor polymer with units reactive to ESIPT was used, however reaching only 1 cd m-2 and 12 mA cm ^-2 .

[066] The devices in PFO presented two emission sets (Figure 7), one relative to the polymer of blue color (420-498 nm) and another one of green color (500-650 nm). In comparison with pure PFO (L = 213 cd m-2, J = 3.0 A cm-2, h = 0.1 cd Al), emissions at 514 nm and 518 nm were attributed to the T * form of BTS, depending on the concentration. For the WOLEDs produced with the mixtures, the 0.5% and 1.0% molar fractions offered the best performances, being very similar in terms of luminance (492 cd m-2 and 439 cd m-2, respectively), but density very different currents (10.0 A crrr ² and 60.0 A crrr ² , respectively). PFO with 2.5 mol / mol% of BTS lights up at a much higher voltage (Von = 16.5V), similarly to dilution in PVK, again as a consequence of aggregation. However, PFO: BTS resulted in white light, with the best device for doping 0.5 mol / mol% and CIE 1931 coordinates at (0.23; 0.30).

 Table 1 - Summary of the electronic optical parameters obtained by all WOLEDs.

 aThe current density values correspond to the maximum luminance.

[067] Therefore, through the tests performed, it is proved that the application of BTS as an active layer is highlighted by having an emission spectrum covering practically the entire region of the visible due to a chemical reaction that occurs when the system is subjected to a electrical potential, a fact of extreme relevance for the production of white emission diodes (WOLEDs). Thus, the use of its electro-emission can occur in different ways depending on the color you want to obtain: it can be deposited as a single active layer and optimized its proportion or by mixing with other active layers, which allows the use of energy transfer processes as an alternative to improve performance.

Claims

 1. Synthesis of a compound of the fluorophores class characterized by the fact that it comprises the steps of:  a) Add 0.2 mmol of 2- (3 ', 4'-diaminophenyl) benzothiazole and 0.4 mmol of salicylic aldehyde in ethanolic medium;  b) Heat the mixture to reflux; and  c) Filter, wash and recrystallize the mixture.  2. Synthesis, according to claim 1, characterized by the fact that, in step "b", the mixture is preferably heated to reflux for 24 hours.  3. Synthesis, according to claim 1, characterized in that, in step "c", the product precipitated in the reaction medium is vacuum filtered and washed with cold ethanol; and then the compound is dissolved in ethanol / tetrahydrofuran (EtOH / THF) under heating, where the ambient temperature is reached naturally to form the crystals.  4. Synthesis, according to claim 3, characterized in that the precipitated product is an orange solid with preferably 90% yield.  5. Compound of the fluorophores class characterized by the fact that it has a chemical structure (1)

and have ¹ H NMR (500 MHz, DMSO-d6, õ = ppm) 6.52 - 6.59 ppm (m, 2H), 6.73-6.80 ppm (d, 2H, J = 8.5 Hz), 7.25-7.32 ppm (t, 2H, J = 7Hz), 7.42-7.56 ppm (dd, 2H, J = 7Hz), 7.47- 7.62 ppm (dt, 2H, J = 7.5 Hz), 8.06 ppm (s, 2H), 8.09-8.18 ppm (dd , 2H, J = 8Hz), 8.49 ppm (s, 1H), 9.06 ppm (s, 1H) and 9.15 ppm (s, 1H). Infrared (cm-1): 3058 (V CHarom), 1609-1592 (VC = N), 755 (V CS).  6. Compound, according to claim 5, characterized by the fact that it presents reactivity of the system in terms of photoreation of proton transfer in the excited state (ESIPT) and tautomeric equilibrium formed in the excited state (N <-> T), and if find in its protonated (N) and deprotonated (A) form in the ground state.  Compound according to claim 5 or 6, characterized in that it is obtained according to the synthesis described in any one of claims 1 to 4.  8. Use of the fluorophor class compound characterized by the fact that it is for application in light emitting diodes, in which the compound is as defined in any one of claims 5 to 7.  9. Use, according to claim 8, characterized by the fact that it is applied as a single active layer or a mixture of layers in optoelectronic devices, preferably white emission devices (WOLEDs).  10. Use, according to claim 8 or 9, characterized by the fact that it is for forming complexes with transition metals or as an analyte for quantifying metal ions in solution. 11. Process for obtaining organic emitting diodes white light (WOLEDs) characterized by the fact of understanding the steps of: a) Wash the ITO substrates (25 W crrr ² ) in an ultrasound bath with a mixture of solvents; b) Deposit at least one layer of poly (3, 4-ethenodioxythiophene) -poly (styrenesulfonate) (PEDOT: PSS) by spin-coating methodology; c) Deposit at least one layer of thickness 60 to 70 nm of the physical mixtures of semiconductor polymers: BTS (0.5%, 1.0% and 2.5% mol / mol) from a solution in tetrahydrofuran (2.6 ^and 10 ² mol L ^_1 ) under an inert atmosphere; d) Evaporate a thick layer of metallic calcium and aluminum by thermal evaporation.  Process according to claim 11, characterized in that in step "a", alternatively, the glass substrate covered by ITO is replaced by a flexible material substrate; and said mixture of solvents comprises the solvents selected from the group consisting of deionized water, isopropyl alcohol, neutral detergent and acetone, in which more specifically the washing is carried out in stages, firstly in a mixture of distilled water and neutral detergent ( 50% / 50% v / v), followed by acetone and later isopropyl alcohol; where, preferably, the washing of the substrates is carried out in 15 minutes. 13. Process, according to claim 11, characterized by the fact that in step "b", the spin-coating parameters are preferably 5000 rpm of agitation for 60 s, in which annealing is carried out for at least 30 min at 110 ⁰ C. 14. Process according to claim 11, characterized in that the semiconductor polymers are poly (iV-vinylcarbazole) (PVK) and poly [9,9-dioctylfluorenyl-2,7,7-diyl] (PFO) polymers, and the BTS compound is as defined in any one of claims 5 to 7. 15. Process according to claim 11 or 14, characterized in that in step "c", alternatively, the PFO devices comprise at least one extra layer of PVK (2.6 x 10 ² mol / L) deposited on the ITO à, preferably 3000 rpm for 60 s, in which the inert atmosphere chamber is adjusted to the lowest possible conditions, such as [H ₂ 0] <1 ppm and [0 ₂ ] <40 ppm.  16. Process according to claim 11, characterized by the fact that in step "d", a layer of metallic calcium (30 nm) and aluminum (100 nm) is preferably evaporated by thermal evaporation with the aid of an evaporation chamber . 17. White light-emitting organic diodes (WOLEDs) characterized by the fact that they comprise a glass substrate covered with tin doped indium oxide (ITO) and polystyrene poly (3,4-ethylenedioxythiophene) sulfonate (PEDOT: PSS); and from 0.5 to 2.5% PVK: BTS, preferably 2.6 x 10 ² mol / L; and from 0.5 to 2.5% PFO: BTS, preferably 2.6 x 10 ² mol / L.  18. Diodes, according to claim 17, characterized by the fact that in a preferred mode they comprise:  glass | ITO | PEDOT: PSS | PVK: BTS (0.5%, 1.0% and 2.5 mol / mol%) | Ca | Al; and glass | ITO | PEDOT: PSS | PVK | PFO: BTS (0.5%, 1.0% and 2.5 mol / mol) | Ca | TO 1.  19. Diodes according to claim 17 or 18, characterized in that they are encapsulated with an epoxy resin.  20. Diodes according to claim 17, characterized in that they alternatively comprise flexible material substrates.  21. Diodes according to any one of claims 17 to 20, characterized by the fact that they are obtained according to the process defined in any one of claims 11 to 16.