A first principles based prediction of electronic and nonlinear optical properties towards cyclopenta thiophene chromophores with benzothiophene acceptor moieties

In the current work, organic cyclopenta-thiophene (CPT) based derivatives (FICR and FICD1–FICD5) were designed by the modulation of end-capped acceptor group of the reference molecule i.e., FICR, to explore their nonlinear optical (NLO) response. The effect of terminal acceptor and donor groups in the tailored compounds was explored by using DFT based quantum calculations. The UV–Vis analysis, frontier molecular orbitals (FMOs), transition density matrix (TDM), natural bond orbitals (NBOs), density of states (DOS), nonlinear optical (NLO) analyses were performed at M06/6-311G(d,p) functional. The LUMO–HOMO band gaps of FICD1–FICD5 were found to be smaller (1.75–1.92 eV) comparative to FICR (1.98 eV). Moreover, the global reactivity parameters (GRPs) were correlated with the results of other analyses. FICD2 and FICD5 with lowest band gap 1.73 and 1.75 eV showed less hardness (0.86 and 0.87 eV, respectively), high softness (0.58 and 0.57 eV⁻¹), and larger absorption spectrum (815 and 813 nm) in gaseous phase and (889 and 880 nm) in solvent phase among all entitled compounds. All the designed chromophores (FICD1–FICD5) demonstrated a significant NLO response as compared to FICR. Particularly, FICD2 and FICD5 exhibited the highest average linear polarizability (<α>) [2.86 × 10⁻²² and 2.88 × 10⁻²² esu], first hyperpolarizability (β_tot) (8.43 × 10⁻²⁷ and 8.35 × 10⁻²⁷ esu) and second hyperpolarizability (γ_tot) (13.20 × 10⁻³² and 13.0 × 10⁻³² esu) values as compared to the other derivatives. In nutshell, structural modeling of CPT based chromophores with extended acceptors, can be significantly utilized to achieve potential NLO materials.