Extrusion of carbon with SON in heterocycles for enhanced static and dynamic hyperpolarizabilities and light harvesting efficiencies

Abstract

The current study investigates the electronic, spectroscopic, and nonlinear optical (NLO) properties of cyclic pyrrole/furan/thiophene (CPFT) compounds and their derivatives using density functional theory (DFT) calculations. The electronic and absorption characteristics were analyzed using four methods—B3LYP-D3, M06-2×, CAM-B3LYP, and ωB97XD—with the 6-311G (d, p) basis set. Molecular geometries were optimized, and frontier molecular orbital (FMO) analysis was performed to understand structure-property relationships. Compound 1d exhibited the smallest HOMO-LUMO gap (3.79 eV) and the highest NLO response due to the presence of an electron-donating -NH₂ group. Molecular electrostatic potential (MEP) analysis identified electron-rich (nucleophilic) and electron-deficient (electrophilic) regions within the molecules. The introduction of reducing and oxidizing agents significantly influenced the total NLO polarizability. Dipole moment (μ), linear polarizability (α_₀), static and dynamic second-order NLO polarizability (β) and light harvesting efficiencies were calculated for all compounds. 1d displayed the largest static second-order NLO response (12,846 a.u.), approximately 1252 times greater than other derivatives and higher LHE of 97 %. Electron localization function (ELF-π) and localized orbital locator (LOL-π) analyses confirmed enhanced electron delocalization in the series-1 compounds. Time-dependent DFT (TD-DFT) calculations determined excitation energies, oscillator strengths, and absorption wavelengths. The absorption spectra showed maximum peaks between 423 and 500 nm for series-1 as compared to series-2 and series-3, supporting strong NLO activity. Frequency-dependent hyperpolarizability at longer wavelengths (1460 and 1907 nm) further enhanced NLO responses. Natural bond orbital (NBO) analysis revealed stabilizing hyperconjugative interactions. These findings demonstrate that CPFT derivatives are promising candidates for optoelectronic and NLO applications, providing a foundation for designing advanced functional materials.