Patent Application: US-14729108-A

Abstract:
new , highly photoluminescent compounds are described having structural formula wherein : r 1 , r 2 , r 3 , r 4 , independently from each other , represent h ; alkyl , alkenyl ; aryl ; — n — ch 3 . these compounds are highly photoluminescent and have high quantum yield ; they have optimal plasticity characteristics and optimal miscibility with other amorphous polymers ; they lead to the formation of thin , stable and uniform layers of photoluminescent material , obtainable by simple techniques of deposition from solution . a simple and high yield process is described for obtaining the aforesaid compounds . in addition , the use of the compounds of formula and their polymer derivatives is described in the preparation of electroluminescent devices , for example leds .

Description:
in the compounds of formula ( i ), the preferred meaning for r 1 , r 2 , r 3 and r 4 is alkyl . as a non - limiting example , r 1 and r 2 can represent c 1 - c 3 alkyl , for example methyl ; r 3 and r 4 can represent c 1 - c 12 alkyl , or c 3 - c 15 alkyl , or c 4 - c 8 alkyl , for example c 6 alkyl . a particularly preferred class of compounds of formula ( i ) is that in which r 1 ═ r 2 and r 3 ═ r 4 . a particularly preferred compound of formula ( i ) is the dimethyl ester of ( 2 , 2 ′ dihexylamino - 4 , 4 ′ dicarboxy ) stilbene acid ( dasde ), having structure : further preferred compounds of formula ( i ) are ( 2 , 2 ′ diamino - 4 , 4 ′ dicarboxy ) stilbene acid ( r 1 ═ r 2 ═ r 3 ═ r 4 ═ h ), and its corresponding dimethyl ester ( r 1 ═ r 2 ═ ch 3 , r 3 ═ r 4 ═ h ). one embodiment extends to the polymers obtainable via polymerisation of the monomer of formula ( i ). examples of such polymers are polyesters , polyamides or polyoxydiazoles , etc . and can be obtained by means of per se known polymerisation reactions . as detailed below , the synthesis of the compounds of formula ( i ) is simple and low - cost . the compounds of formula ( i ) have shown an optimal solubility in organic solvents and a high ease of deposition in monolayer film , for example by means of spin - coating technique : the films thus obtained have shown optimal morphological stability . the quantum emission yield is particularly high . the compounds of formula ( i ) moreover have optimal miscibility with amorphous and / or electroconductive polymers , in particular polyvinylcarbazole and polyvinylpyridine , allowing the preparation of transparent leds with high structural uniformity , with uniform and reproducible conductivity characteristics . overall , the aforesaid characteristics allow preparing high quality electroluminescent devices with low production costs ; such characteristics are advantageously maintained also for the products deriving from polymerisation of the compounds of formula ( i ). in a further embodiment , a method is described for synthesising the compounds of formula ( i ). in its general form , the method comprises the following characteristic steps : a ) reduction of the ( 2 , 2 ′ dinitro - 4 , 4 ′ dicarboxy ) stilbene acid of formula ( ii ) to ( 2 , 2 ′ diamino - 4 , 4 ′ dicarboxy ) stilbene acid of formula ( ia ), corresponding to the compound of formula ( i ) in which r 1 ═ r 2 ═ r 3 ═ r 4 ═ h . the further compounds of formula ( i ) in which at least one of r 1 , r 2 , r 3 , r 4 , is different from h , are obtained by applying the following additional steps : b ) esterification of the 4 and / or 4 ′ carboxy groups of the compound ( ia ), obtaining the compounds of formula ( ib ) the compounds of formula ( i ) where r 3 and / or r 4 are not h , are obtained by means of : c ) alkylation of the compound ( ia ) or ( ib ) in the 2 and / or 2 ′ diamino positions . the reduction reaction a ) can be carried out by means of per se known techniques , for example by heating the compound ( ii ) in an aqueous solvent in presence of sodium sulphide . the esterification reaction b ) can be carried out by means of treatment with a suitable alcohol in acidic conditions ; the alcohol used depends on the type of ester substituent desired ; for example , methanol leads to products of formula ( ib ) where r 1 ═ r 2 ═ ch 3 , etc . compounds with r 1 different from r 2 can be obtained by working in selective esterification conditions , for example using half moles of esterifying agent with respect to those necessary for complete esterification , and / or using appropriate protective groups of one of the two — cooh functions , according to per se known techniques . the alkylation reaction c ) can be carried out by treating the compound of formula ( ia ) or ( ib ) with a suitable alkyl halide , in basic conditions , and in presence of a suitable solvent , for example dimethylformamide . the halide used depends on the type of alkyl substituent desired : for example , hexylbromide leads to products where r 1 ═ r 2 ═ c 6 h 13 ; compounds with r 1 different from r 2 can be obtained by operating in selective alkylation conditions , e . g . using half moles of alkylating agent with respect to those necessary for complete alkylation , and / or using suitable protective groups of one of the two amine positions , according to per se known techniques . the dinitroderivative ( ii ) is obtainable , for example by reacting 3 - nitro -( 4 - chloromethyl ) benzoic acid ( iii ) with a suitable alcohol in alkaline environment ; the alcohol used is e . g . ethanol ; the alkali is e . g . koh . 3 - nitro -( 4 - chloromethyl ) benzoic acid ( iii ) is obtainable , for example , via nitration of 4 - chloromethylbenzoic acid ( iv ) the reaction can be carried out by treating the compound ( iv ) with concentrated sulphuric acid and nitric acid . one embodiment also provides the chemical - physical characterisation of compounds of formula ( i ), particularly advantageous for applications in pled devices , both as monomers and as a polymer obtained therefrom . in particular , the compounds are advantageously usable as a single active layer in electroluminescent devices emitting in the visible light range , in particular in the green range . one embodiment comprises the compounds of formula ( i ), as previously described , in the preparation of electroluminescent devices , for example leds . the preparation of the devices occurs according to per se known techniques : as a non - limiting example , the compound of formula ( i ), or its polymerised correspondent , is dissolved in a suitable solvent and then deposited onto suitable supports by means of spin coating or jet - printing . in the preparation of the devices , the compound of formula ( i ) can be used as such , or in blends with the above mentioned amorphous polymers . the resulting devices ( generally diodes ) being highly luminescent and with excellent stability , plasticity and transparency , can be used as components , for example , of screens of cellular phones , computers , televisions , photo / videocameras , displays or light indicators for electronic instruments , road signs , lighting devices , etc . the invention is further illustrated in non - limiting manner by means of the following examples . the innovative monomer , derived from stilbenecarboxylic acid ( dasde ), was synthesised by means of nitration , reduction and alkylation reactions . in fig1 , the general synthesis scheme is reported with the related synthesis processes of the various steps for obtaining dasde . 230 ml of 96 % sulphuric acid are poured into a 500 ml flask and 130 ml of fuming nitric acid are slowly added under stirring . the above is cooled through a water and ice bath to a temperature of 0 ° c . at this point , 10 g ( 0 . 0580 mol ) of reagent [ 2 ] are added , small portions at a time . the reaction continues for about 90 min , in which it is important that the reagent is completely dissolved inside the acid mixture . one then proceeds with the recovery by pouring everything into about 700 ml of water and ice . a solid white substance precipitates , which is filtered off and subsequently washed in a beaker in order to remove the acid residues . the crystallisation occurs in toluene . 1 h nmr ( 200 mhz cdcl 3 ) δ 8 . 76 ( s , 1h ); 8 . 36 ( d , 1h ); 7 . 87 ( d , 1h ); 5 . 03 ( s , 2h ) 45 ml of absolute ethanol are poured into a 250 ml beaker and 5 . 47 g ( 0 . 0970 mol ) of koh are slowly dissolved therein . at this point , 5 . 00 g ( 0 . 023 0 mol ) of 3 - nitro -( 4 - chloromethyl ) benzoic acid are added . the precipitation of a brownish powder in the system immediately starts , being the potassium salt of dinitro - stilbenedicarboxylic acid . the system is left to react at room temperature for a time of about 45 minutes . the salt is filtered off under vacuum and is dissolved in about 70 ml of water , if necessary increasing the temperature until complete dissolution occurs . at this point , the acid is precipitated with hcl , until ph 1 is reached . the solid product is recovered , which we then dry in the stove . 1 h nmr ( 200 mhz dmso ) δ 7 . 62 ( s , 2h ); 7 . 89 ( d , 2h ); 8 . 52 ( d , 2h ); 9 . 06 ( s , 2h ); 11 . 0 ( s , 2h ) 100 ml of distilled water are poured into a 250 ml beaker and 6 . 90 g ( 0 . 0288 mol ) of sodium sulphide are dissolved therein . once the salt is dissolved , 5 . 00 g ( 0 . 0138 mol ) of dinitrostilbenedicarboxylic acid are added . the system is kept boiling for a time of 15 min . at this point , under stirring , hydrochloric acid is added up to a ph 4 - 5 . ( 2 , 2 ′ diamino - 4 , 4 ′ dicarboxy ) stilbene acid is precipitated , which is re - dissolved and re - precipitated in aqueous solution so to remove possible residues containing sulphur . the product is dried in an oven at 120 ° c . such acid , in organic solution , has luminescence under uv lamp , a quality not shown by the starting dinitro derivative . 1 h nmr ( 200 mhz dmso ) δ 6 . 27 ( s , 4h ); 7 . 05 ( s , 2h ); 7 . 24 ( d , 2h ); 7 . 30 ( s , 2h ); 7 . 46 ( d , 2h ). 200 ml of methanol were inserted in a 500 ml flask along with 11 . 6 g ( 0 . 0390 mol ) of diaminostilbenedicarboxylic acid . 15 ml of 96 % sulphuric acid were carefully added under stirring . the system is then left to reflux for about 5 hours . after about two hours , further 50 ml of methanol are added into the flask and the reflux is continued . the colour of the system is red - brown . the recovery is made by pouring into a beaker containing about 600 ml of water and ice , to which a solution of concentrated naoh is added until ph 8 is reached . at this point , the product is filtered off and further washed in a beaker with 300 ml of water , after which it is dried in a stove at 120 ° c . 1 h nmr ( 200 mhz dmso ) δ 3 . 89 ( s , 6h ); 7 . 05 ( s , 2h ); 7 . 10 ( d , 2h ); 7 . 15 ( s , 2h ); 7 . 36 ( d , 2h ) 5 . synthesis of the hexyl derivative of the methyl diester of ( 2 , 2 ′ diamino - 4 , 4 ′ dicarboxy ) stilbene acid ( dasde ) 15 . 0 g of k 2 co 3 ( 0 . 108 mol ) in 40 ml of dmf are poured into a flask , and the system is left under stirring . in the meantime , 4 . 00 g ( 0 . 0122 mol ) of the aminostilbene ester are weighed and added inside the flask . the above is left under stirring for about 20 minutes , after which 35 . 0 ml ( 0 . 250 mol ) are slowly added of 1 - bromohexane . at this point , the system is brought to reflux and the reaction proceeds for two days . on the third day , recovery is carried out by filtering the salts and collecting the solution in dmf in a flask , together with a chloroform solution ( 2 × 50 ml ) with which the salt was repeatedly washed . all is dried and the result is a very dense oil , also due to the presence of residual salts . an extraction with chloroform is then carried out and the organic phase is dehydrated and once again dried . a clear oil is thus obtained containing the product desired . such oil is thus poured into a beaker , in which heptane is added , and under stirring , heptane is brought nearly to boiling . three extractions are thus made ( 70 , 50 , 50 ml ) of heptane , so as to extract dasde and the more alkylated products , leaving the non - alkylated products within the dark oil . the solution in heptane is brought to boiling and filtered to remove impurities , and finally brought to a small volume ( about 50 ml ). after cooling , dasde crystals are obtained , which can be separated , and the mother liquors contain the molecules with a greater number of alkyl chains that can be separated chromatographically . 1 h nmr ( 200 mhz cdcl3 ) δ 7 . 39 ( d , 2h ); 7 . 07 ( s , 2h ); 7 . 04 ( d , 2h ); 6 . 88 ( s , 2h ); 3 . 89 ( s , 6h ); 3 . 35 ( t , 4h ); 1 . 63 - 0 . 85 ( m , 22h ). the 1 h - nmr spectra were carried out of the stilbenedicarboxylic acid derivatives . the diagrams related to the dinitro derivative are illustrated in fig2 ; those related to the diamine derivative are illustrated in fig3 . in the reduction step of nitro - to amino groups a substantial change in the aromatic signals is observed , coupled inter alia with a change in the luminescent properties of the molecule , becoming evident after reduction . fig4 a - 4 d show the enlargements of the aromatic parts of both compounds , so to better observe their differences . as evident by comparing the aromatic parts , the reduction of the nitro groups leads to an overall shift of the benzyl protons towards lower σ . in particular , the signal related to the proton d overlaps with that of proton a , and in addition there is a shift towards the outside of the protons c and b , such that the signal d + a is set between the two . differential thermal analyses ( dsc ) were carried out of the amine derivative of the stilbenecarboxylic ester and of dasde . the nitro derivative , obtained in the acid form , was analysed up to 250 ° c ., at which temperature the decomposition starts . at the same temperature , the nitroderivative in ester form also did not show any melting . in fig5 and 6 we show the thermograms carried out on the two compounds . as seen from both thermograms , two crystal forms are present . this is more evident in the amine derivative , in which a first melting is observed around 190 ° c . with partial recrystallisation and melting of the second phase around 215 ° c . an ortep structural characterisation was carried out of dasde by means of x - ray diffraction on a single crystal . in fig7 , a projection of the molecule is reported . symmetry operation used for generating the equivalent atoms : *=− x , − y , − z . the molecule has a c 2 symmetry and lies on a crystallographic inversion centre . below , the bond distances are reported in angstroms ( å ) along with the angles (°) for several selected atoms of interest ( tables 1 - 2 ). the crystals adapted for the x - ray diffractometric analysis were obtained from heptane solution via slow evaporation at room t . they have the aspect of small prisms with yellow colour . the data collection for the structural resolution was carried out under nitrogen flow , at 173 k , on a bruker - nonius diffractometer kappa ccd , using the radiation kα of molybdenum ( 0 . 71069 å ). the structure was resolved with direct methods ( sir 97 ) [ 3 ], subsequent fourier transforms , and refined with the minimum squares method ( shelxtl ) [ 4 ]. a semi - empirical correction was carried out by using the program sadabs . the hydrogen atoms were positioned based upon geometric considerations , with the exception of the olefin and amine hydrogen atoms . the final refinement was carried out by using anisotropic thermal parameters for all atoms different from hydrogen . the structural analysis shows that the molecule is nearly planar , with the nitrogen atoms contained in the plane defined by the aromatic rings ; moreover , the distance ( 1 . 976 ( 3 ) å ) between the hydrogen atoms h ( c 1 ) and h ( n 1 ), accounts for the experimental difficulty in obtaining the dialkylated form of this molecule . a second alkyl group , in fact , would be affected by a strong steric hindrance due to the presence of the stilbene proton . the dialkylation of the nitrogen would then lead to a forced distortion of such system , sacrificing the strong conjugation of the nitrogen with the aromatic ring . the planar structure of the molecule highlights the extension of the conjugation , responsible for the fluorescence activity , and favours the morphological stability of the polymer films . the quantum yield signifies , for a given substance , the ratio between the emitted and absorbed photons . it is therefore a direct indication of the quantity of energy emitted through a mechanism of radiative type . in order to evaluate the quantum yields , we used a method present in literature , which provides for the comparison of said values with the quantum yields of suitable standards [ 5 - 6 ]. we first estimated the quantum yield of known substances obtained with our equipment , in order to calibrate the method . the method used requires measuring absorption and photoluminescence of diluted solutions of the fluorescent substances under examination . the standards used are quinine sulphate and fluorescein . the absorption and fluorescence spectra of the quinine sulphate are reported in fig8 . the fluorescence spectra were obtained by exciting the samples at a wavelength relative to a maximum absorbance of the sample of less than one . in such a manner , by comparing the values obtained with the respective emission areas , a series of points are obtained which are aligned along a straight line . by collecting the data for solutions with different concentrations , straight lines are obtained from whose slope it is possible to obtain the quantum yield of fluorescence via the following expression . φ x = φ st ( grad x / grad st )*( η 2 x / η 2 st ) φ ( x ; st ): quantum yield of an unknown sample and a reference sample grad ( x ; st ): angular coefficient of the line related to an unknown sample and a reference sample η ( x , st ): refraction index of the solutions ( in practice , it is that of the solvent , the solutions being very diluted ). in order to calibrate the method , the quantum yield was calculated of a substance from the quantum yield of the other standard and by comparing the value with that known in literature . thus , the quantum yields were calculated of fluorescein dissolved in a solution of 0 . 1m naoh and of quinine sulphate dissolved in a solution of 0 . 1m sulphuric acid . fig9 reports the calibration lines . table 4 reports the obtained quantum yield values . the fluorescence spectrum shows an emission maximum at around 530 nm , thus it can be stated that such molecule is a good candidate for making devices which emit in the green range . the calculated quantum yield of such material is 0 . 535 . in fig1 , the graph is reported showing the dasde line in comparison with that of the standards which we have used ; table 5 shows the calculated quantum yields . table 5 shows that the quantum yield of dasde which we synthesised is comparable to that of quinine sulphate . this indicates a high emission efficiency for such substance . the data shown above have indicated a quantum emission efficiency equal to 0 . 535 for the monomer dasde , being comparable to the quantum yield of the quinine sulphate ( 0 . 546 ). such monomer was found to be particularly soluble in most organic solvents and miscible in amorphous polymers of different nature . in fact , blends were made by using 0 . 3 % by weight of dasde in polymer matrices , such as and polyvinylpyridine ( pvpy ) and polyvinylcarbazole ( pvk ). the films obtained from these blends resulted unaltered after a period of over six months . in addition , strong emissions were registered from the polymer films even with small quantities of dasde . these data are very promising , also in view of the ease of monomer synthesis and the relatively low cost of the starting reagents . in addition to being polymerised via dispersed phase , such monomer can be polymerised through the acid functions , thus obtaining polymers of different nature such as polyesters , polyamides or polyoxydiazoles . it is therefore possible to make monolayer polymer devices by means of organic solution deposition , with high quantum efficiency . the various embodiments above can be combined to provide further embodiments . all of the u . s . patents , u . s . patent application publications , foreign patents , foreign patent applications and non - patent publications referred to in this specification and / or listed in the application data sheet incorporated herein by reference , in their entirety . aspects of the embodiments can be modified , if necessary to employ concepts of the various patents , applications and publications to provide yet further embodiments . these and other changes can be made to the embodiments in light of the above - detailed description . in general , in the following claims , the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims , but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled . accordingly , the claims are not limited by the disclosure . t . v . luh , s . bosu , r . m . chen ; 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