Structural and Spectroscopic Properties of Homo- and Co-Oligomers of o-Phenylenediamine and o-Toluidine: Theoretical Insights Compared with Experimental Data

Density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations have been performed to get insights into the structural, optical, and electronic properties of homo- and co-oligomers of o -phenylenediamine (OPD) and o - toluidine (OT). UV–vis spectral bands assigned to various neutral, cationic and dicationic homo- and co-oligomers of OPD and OT have been analyzed at TD-DFT UB3LYP/6-31G (d, p) level, and complete assignments/correlation with experimental results are reported. The calculated vibrational bands of both homo- and co-oligomers of OPD and OT at B3LYP/6-31G (d) level along with their assignments are compared with experimental frequencies. Electronic properties such as ionization potentials ( I P ), electron affinities ( E A ) and HOMO–LUMO bandgap energies of both homo- and co-oligomers of OPD and OT have been calculated and are compared in the present work. DFT calculations with the 6-31 G (d) basis set predict very accurately experimentally observed vibrational modes as well as energy bandgap values.