A series of donor⁻π-conjugated spacer⁻acceptor (D⁻π⁻A) organic dyes featuring an azobenzene spacer were designed as chromic dyes and investigated computationally. The electron-donating strength was modified by introducing electron-donating units to the donor side. In particular, the trans⁻cis isomerization of the azobenzene-based dyes and its effect on the optical and electronic properties were further scrutinized. In both trans and cis conformers, a gradual increase in electron-donating strength promoted the natural charge separation between donor and acceptor moieties, thereby allowing the absorption of a longer wavelength of visible light. Importantly, the conformational change of the azobenzene bridge resulted in different absorption spectra and light-harvesting properties. The azobenzene-based dyes will open up a new research path for chromic dye-sensitized solar cells.
Keywords: Dye-sensitized solar cell (DSSC); donor–π-conjugated spacer–acceptor (D–π–A) azobenzene-based dyes; intramolecular charge transfer; time-dependent density functional theory (TDDFT).