Theoretical and experimental insights into the properties of donor-σ-acceptor type derivatives of quinoxaline and methanone containing different donor moieties

Abstract

Three compounds, bearing a quinoxaline-methanone unit as an acceptor moiety and dimethylacridan, carbazole, or phenothiazine donor moieties, were designed and synthesized by employing the single-step Buchwald-Hartwig cross-coupling reaction. The geometry and electronic characteristics of the compounds in the ground and the first singlet excited states were studied within density functional theory (DFT). It was shown that S0 → S1 excitation is characterised by intramolecular charge transfer (ICT) from the donor moieties to acceptor quinoxaline-methanone moiety for all the compounds. The extent of ICT depends on the dihedral angle between the donor moiety and the phenyl moiety. The red emission of the derivatives of quinoxaline-methanone and dimethylacridan or phenothiazine was found to be delayed fluorescence. The films of 2 wt% solid solutions of the derivatives of quinoxaline-methanone and dimethylacridan, or phenothiazine in poly(metylmethacrylate) showed moderate photoluminescence quantum yields of 16% and 11%, respectively, and the lifetimes of delayed fluorescence of 5.56 μs and 99.1 μs. The films demonstrated emission sensitivity to oxygen.