Multifunctional quinoxaline containing small molecules with multiple electron-donating moieties: Solvatochromic and optoelectronic properties

Two multifunctional quinoxaline containing small molecules (designated as: SD-1 and SD-2) composed of electron-donating (D) moieties both in vertical and horizontal directions to an electron-accepting (A) quinoxaline at the central position have been synthesized. In both SD-1 and SD-2, the dimethylaminobenzene (DMAB) and triphenylamine (TPA) groups were used as an electron-donor in the vertical direction, and dihexyloxy-functionalized TPA was adapted as an additional donor in the horizontal direction. The unique donor (D)–acceptor (A) structures around the central quinoxaline moiety impart special solvatochromic and optoelectronic features to the SD-1 and SD-2. Photovoltaic cells (PVCs) and organic light-emitting diodes (OLEDs) were fabricated from SD-1 and SD-2 by solution processing (i.e. spin-coating). While PVCs with a structure of ITO/PEDOT:PSS/SD-1 or SD-2:PC71BM/Al show the power conversion efficiencies of 0.31% and 0.45%, respectively, OLEDs with a structure of ITO/PEDOT:PSS/SD-1 or SD-2/LiF/Al exhibit a maximum luminance (efficiency) of 7.42 cd/m2 (0.034 cd/A) and 48.84 cd/m2 (0.032 cd/A) with a turn-on voltage of 3.6 and 2.4 V, respectively. Furthermore, the Commission Internationale de L’Eclairage (CIE) chromacity coordinates of the OLED device with SD-2 were (0.67, 0.32), which are very close the CIE chromacity coordinates (0.67, 0.33) of National Television Society Committee (NTSC) for red color. Owing to their promising stimuli-responsive properties and device performances, these D–A molecules with unique structures can be considered as good candidates for multifunctional sensory and optoelectronic applications.