Solvent-dependent electronic, photophysical and nonlinear optical properties of azulene-based push-pull chromophores: A DFT approach

This work presents a computational analysis of a series of azulene-based push-pull chromophores (A1–A10) with customized nonlinear optical (NLO) characteristics, targeting advanced applications in photonics and optoelectronics. By employing density functional theory (DFT) and time dependent-DFT (TD-DFT), we systematically assessed the influence of solvent polarity on first, second, and third order polarizabilities, natural transition orbitals, and UV–Visible absorption spectra. The key results indicate that strategic acceptor substitutions and extended conjugation length lead to enhanced multi-order nonlinear optical responses, with the derivative A8 showing remarkable octupolar contribution. The reduction in the energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) has promoted effective intramolecular charge transfer, especially in derivatives A6, A7, A9, and A10, which displayed all-order NLO characteristics. In contrast, A2 and A4 were characterized by predominant second-order responses, while A8 exhibited both first and third order responses. By correlating solvent environments with nonlinear optical performance, this computational study demonstrates dynamic tunability of these materials, which paves the way for their applications in optical limiters, photomultipliers and photorefractive devices. The findings of this study highlight the promise of azulene derivatives as flexible building blocks for the next generation of photonic and optoelectronic technologies.