Synthesis of D-A based violet-red light emitting indolo[2,3-b] quinoxalin-2-yl(phenyl)methanone amine dyes: Opto-electrochemical, AIE, and theoretical properties

In this work, we have designed and synthesized seven new amine derivatives of indolo[2,3-b]quinoxalin-2-yl(phenyl)methanone through the use of palladium-catalyzed Buchwald-Hartwig (C-N) coupling amination reaction and characterized by spectroscopic methods. Molecules offers intramolecular charge transfer (ICT) transitions, which result in absorption spectra with longer wavelengths (lambda(max) = 385-509 nm), resembling a donor-acceptor (D-A) assembly. Consequently, the dyes emit light in violet-red region (lambda(emi) = 406-637 nm) in solution and solid film. Moreover, dye 5 and 6 demonstrate aggregation-induced emission (AIE) in THF-Water system due to the formation of nanoaggregates. Electrochemical properties investigated using cyclic voltammetry. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were determined within the range from -4.91 to -5.76 eV and -3.03 to -3.45 eV, respectively, and comparable with reported ambipolar materials. Theoretical studies also conducted using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, which agreeing with experimental data. The small energy difference between singlet (S-1) and triplet (T-1) states (triangle E-ST = 0.24-0.45 eV) suggests that these dyes possess thermally activated delayed fluorescence (TADF) emitting properties. Thus, dyes propose their potential application in optoelectronic devices.