Unveiling charge transfer kinetics and static-dynamic nonlinear optical switching in 2-phenylthiophene push-pull...

Addressing the growing demand for ultrafast photonic nonlinear optical (NLO) materials, ultrafast switching NLO behaviour was studied in detail in 2-phenylthiophene-based push-pull chromophores using laser pulses at 532 and 1064 nm. The EOPE β (-ω, ω, 0) and SHG β (-2ω, ω, ω) calculations for these laser pulses demonstrate an incredible NLO response with efficient energetic offsets that are approximately six times larger than BSS-1. Moreover, the correlation between experimental and theoretical dipole moments and UV absorption (λ_(exp) = 397, λ_max = 394.94 nm) is analyzed, emphasizing its impact on developing NLO switching devices. Quantum chemical calculations, such as frontier molecular orbitals (FMOs), UV-Vis investigation, electron-hole overlap analysis, non-covalent interaction (NCI), molecular electrostatic potential (MEP), natural bond orbitals (NBOs), along with static and frequency-dependent NLO were performed to determine the effect of donor and acceptor modification on the enhanced harmonic generation of designed chromophores (BSSR1-BSSR8 and reference BSS-1). Notably, outstanding NLO findings were obtained for nitro and cyano-based acceptor compounds. Interestingly, among all the derivatives, BSSR4 and BSSR5 had the lowest E_gap values of 1.09 and 1.246 eV, respectively, and the E_gap values were found in the following decreasing order: BSS-1 (R) > BSSR1 > BSSR3 > BSSR7 > BSSR6 > BSSR2 > BSSR8 > BSSR5 > BSSR4. Surprisingly, BSSR5 and BSSR4 had maximum NLO (α and β) amplitudes of 8.62 × 10² and 8.09 × 10⁵ a.u in the gas phase, respectively, indicating their potential towards all-optical computing and ultrahigh bandwidth information processing. These findings underscore the significance of charge transfer dynamics and ultrafast NLO switching in 2-phenylthiophene push-pull chromophores, paving the way for advanced harmonic generation and cutting-edge electro-optic applications.