Abstract
In accordance with the concept of conjugation, we havedeveloped a new class of p-aminoisocondensed heteroaromaticpyrroles. These compounds showed interesting photophysicaland electrochemical properties.By our method of retro-malonate addition reaction, we havesynthesized four series of p-aminoisocondensed heteroaromaticpyrroles successfully, namely, (1) p-aminophenylthieno[2,3-c]pyrroles 74 ~ 77 and 80. (2) isoindoles 84 ~ 87 and 90 . (3)tert-butyl 2-(4-aminophenyl)-2,4-dihydropyrrolo[3,4-b]indole-4-carboxylates 95 ~ 98. (4) methyl 2-(4-aminophenyl)-2,4-dihydropyrrolo[3,4-b]indole-4-carboxylates 102 ~ 105.The differential scanning calorimetry (DSC) measurementsrevealed a glass transition temperature of 193.6 ℃ forcompound 74, 147.4 ℃ for compound 98, 29.8 ℃ for compound102, 26.1 ℃ for compound 103, 30.7 ℃ for compound 104,and52℃ for compound 105,but compound 95 ~ 98 started degradingabove melt point. These compounds showed good fluorescenceproperties both in solid and solution states.The fluorescencewavelengths located within 360 ~ 500 nm ( blue-green ) insolution state, and within 340 ~ 460 nm(blue) in solid state.The -NR2 group at the para-position of the phenyl substitientplay an important role in finetuning both the intensity ofandfluorescence of p-aminoisocondensed heteroaromaticpyrroles.By cyclic voltammetry (CV)measurements, we have observed thatthe electrochemicalbehavior of compounds 74, 95, 96, 98, and102 ~ 104 was reversible. According to the redox potentialposition of CV and the onset absorption position of UV-VISspectra, the HOMO, LUMO, and energy gap ( Eg ) for thesecompounds, Alq3, PBD, TPBI, and NPB were estimated using theenergy level of ferrocene as a reference ( 4.8 eV below thevacuum level).In organic light emitting diodes application, compounds 86and 96 were not good emitters. The lifetimes of devices madeform these c ompounds were too short (about 5 ~ 20 sec ).Compounds 75, 76, and 86 were not useful as hole transportmaterial due to their poor electrochemical properties. Usingcompound 96 as a hole transport material and Alq3 and PBD aselectron transport material, the devices do not show a goodI-V curve.