Triphenylamine Functionalized Unsymmetrical Quinoxalines

Abstract

A family of unsymmetrical quinoxalines 11–18 of types D-A-π-D and D-A-A′-D′ have been designed and synthesized by the Suzuki, Heck, Sonogashira, Ullmann coupling and [2+2] cycloaddition−retroelectrocyclic ring opening reactions. A systematic study was performed to explore the effect of donor, acceptor and π-linker on the triphenylamine functionalized quinoxalines. The electronic absorption spectra of the ethynyl bridged quinoxaline 14 show red shifted absorption in the high-energy region compared to quinoxaline 13. The quinoxalines 17 and 18 exhibit red shifted absorption in the near–infrared (NIR) region due to the incorporation of strong TCNE/TCNQ acceptor units. The TGA data reveals that triphenylethylene substituted quinoxaline 15 shows higher thermal stability compared to other quinoxalines. The electrochemical data exhibit strong electronic communication in quinoxalines 11–18. The incorporation of TCNE/TCNQ acceptor units results in greater stabilization of LUMO levels and low HOMO−LUMO energy gap in 17 and 18 which was supported by computational studies. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim