First-principles study of nonlinear optical and electronic properties of A-π-D-π-A configured compounds with novel oligothiophenes

In this work, we investigate the electrical and the optical properties of a new series of four acceptor–donor-acceptor oligothiophenes. In particular, we study the optimized geometries, the natural bond orbital (NBO) analysis, the nonlinear optical (NLO) properties, the Mulliken atomic charges, absorption spectra, and the electronic properties of such molecules using time-dependent density functional theory (TD-DFT) computations at the B3LYP/6-31G(d,p) level. Among others, we find that the resulting low energy band gap (Egap) values from the computed HOMO and LUMO frontier orbital energies can be supported by the NBO evaluation and good NLO response, including the large values of the first-order hyperpolarizability (β)