Synthesis, Spectral, Electrochemical and Theoretical Investigation of indolo[2,3-b]quinoxaline dyes derived from Anthraquinone for n-type materials

A series of five novel dyes based on indolo[2,3-b]quinoxaline skeleton, derived from anthraquinone, have been synthesized through cyclo-condensation reaction in good yield. The photophysical, electrochemical and thermal properties along with computed HOMO-LUMO energy levels were studied for the synthesized compounds. Their absorption and photoluminescence properties were investigated in various solvents and in neat solid film and found to possess characteristic electronic absorption and emission spectra which strongly depend on the nature of solvents used. Compounds show intramolecular charge transfer transitions (ICT) in the range of 501-561 nm with high molar absorption coefficient (epsilon). These indoloquinoxaline derivatives emit in the range of 580-648 nm in solutions and 672-700 nm (red region) in neat solid films. Electrochemical data indicate that the dyes possess relatively low-lying LUMO levels in the range -3.29 to -3.43 eV. The thermal stability observed for these compounds suggests their use under ambient conditions. The in-built donor-acceptor architecture and HOMO-LUMO energies were further rationalized using DFT calculations. This study suggests that these compounds have potential to be used as n-type materials for optoelectronic devices.