On the spectroscopic analyses of thioindigo dye

Highlights: [•] B3LYP as well as FTIR were utilized to analyze thioindigo dye. [•] Vibrational assignments for thioindigo isomers were aided at B3LYP/6-311G(d,p). [•] Cis-isomer is a promising structure for optoelectronic devices as solar cells. [•] Cis-isomer has a high dipole moment (3.44 Debye) and HOMO/LUMO energy gap (3.02 eV)