Phenothiazine-based dyes containing imidazole with π-linkers of benzene, furan and thiophene: Synthesis, photophysical, electrochemical and computational investigation

Abstract

Three newly designed phenothiazine-based dyes 6a-c were synthesized in good yield by introducing 1, 4, 5-triphenyl imidazole to phenothiazine skeleton linked to benzene, furan or thiophene π-linkers and connected with cyanoacrylic acid acceptor as the anchoring, respectively. UV–vis absorption and fluorescence properties of 6a-c were studied in different solvents. Among π-linkers, furan revealed the highest redshift of absorption, followed by thiophene and benzene. The dyes show intense visible absorption with high molar absorptivity; hence good light-harvesting dyes when used as sensitizers. The cyclic voltammetry data revealed that the HOMO energy levels of 6a-c were 5.36 eV for dye 6a and 5.42 eV for dyes 6b and 6c. Also, the energy LUMO levels of 6a-c were -3.10, -3.21, and -3.26 eV for dye 6a-c, respectively. Such well-matched energy levels of these dyes with those reported sensitizers would pave the way for their use in photovoltaic devices. Furthermore, these dyes were investigated by Density Functional Theory (DFT) and time-dependent TD-DFT to explore their potential as efficient dyes in photovoltaic devices. The geometrical structures, optoelectronic properties and charge transfer of these dyes were investigated. The results indicate that the 6a-c dyes have a small energy gap, absorption in the visible and higher oscillator strength. The modification of phenyl, furan and thiophene suggests that these dyes could be effective for dye-sensitized solar cells (DSSCs).