Structural parameter-modulated nonlinear optical amplitude of acceptor–π–D–π–donor-configured pyrene derivatives: a DFT approach

Abstract

In the present study, organic pyrene-based derivatives were selected for NLO investigation. The reference compound named methyl (E)-2-cyano-3-(5-(pyren-1-yl)thiophen-2-yl)-3-acrylate (MCPTR) was taken for the design of its derivatives, abbreviated from MCPTD1 to MCPTD8 compounds. The nonlinear optical (NLO) properties, frontier molecular orbitals (FMOs), natural bonding orbital (NBO), and UV-vis analyses of molecules (MCPTR–MCPTD8) were executed by M06 level with 6-31G(d,p) basis set. The UV-vis investigation showed that all designed compounds exhibited a redshift, and the maximum wavelength was studied in MCPTD7 (832.330 nm). The HOMO–LUMO band gaps of MCPTD1–MCPTD8 were found to be smaller as compared to those of MCPTR (3.210 eV). The global reactivity information was correlated with band gap values; MCPTD7, having a lower band gap, exhibited smaller hardness values (0.0321 E_h) with larger softness values (15.5763 E_h). The natural bond orbital analysis (NBO) helped to elucidate the hyper conjugative interactions, along with the stability and electron-transfer process. The dipole moment (μ), average polarizability 〈α〉, first hyperpolarizability (β_vec) and second hyperpolarizability 〈γ〉 were computed for MCPTR–MCPTD8. Consequently, all designed compounds (MCPTD1–MCPTD8) possessed greater NLO responses than the reference compound (MCPTR). Interestingly, MCPTD7 showed a smaller energy gap and remarkable NLO response among MCPTD1–MCPTD8 compounds. The highest μ_total, 〈α〉, β_vec and 〈γ〉 values for MCPTD7 were observed as 7.200, 2.40 × 10⁻²² esu, 2.84 × 10⁻²⁷ esu and 8.6024 × 10⁷ esu, respectively. Aptitude towards the NLO material relied upon the position of different groups, the conjugated system donor and acceptor regions. The high NLO response reveals the fact that this class of pyrene-based derivatives with a thiophene linker has remarkable contributions towards NLO technological applications.