New diarylaminophenyl derivatives of carbazole: Effect of substituent position on their redox, spectroscopic and electroluminescent properties

Abstract

Three new derivatives of carbazole were synthesized, namely two isomers disubstituted with diarylaminophenyl groups in 2,7- and 3,6- positions (C1 and C2) and diarylaminophenyl symmetrically disubstituted with carbazole C3. All three compounds showed similar electrochemical behavior with one reversible redox couple, originating from the oxidation of the diarylaminophenyl units to radical cations, followed by an irreversible anodic peak associated with the oxidation of the carbazole unit. The electrochemical results were supported by DFT calculations which predicted the same order of ionization potential values as experimentally found. Absorption and emission bands in the spectra of C1 and C3 were bathochromically shifted as compared to the corresponding bands in C2, again consistent with DFT calculations. C1 showed a very high value of the photoluminescence quantum yield in THF solution, i.e. 90%. Moreover, the position of the emission band turned out to be solvent dependent and underwent a hypsochromic shift in toluene with simultaneous decrease of the photoluminescence quantum yield value to 68%. Blue light emitting C1 was used as an electroluminophore in a simple, guest/host-type single-layer light emitting diodes exhibiting luminance exciding 1000cd/m2 and luminous efficiency of 0.7cd/A.