Unveiling the Twisted Aromatic Donor Effect on the Nonlinear Response of D-π-A Type Malononitrile-Derived Chromophores.

ABSTRACT

This study presents the design, synthesis, and comprehensive characterization of a novel series of D-π-A type malononitrile-derived chromophores, BTC-1-BTC-4. Combining various spectroscopic techniques, nonlinear Z-scan measurements, and quantum chemical calculations, we revealed the intricate relationship between nonlinear optical properties and the interplay of molecular structure, intramolecular charge transfer (ICT), and dipole moments (µ). Our experimental and computational findings corroborate that the polarization degree in the ground state, the charge separation in the excited state and twisted intramolecular charge transfer (TICT) collectively dictate the nonlinear optical properties of the compounds. Notably, BTC-1 exhibits an exceptional nonlinear absorption coefficient ß value (2×10-8 m W-1), attributed to its optimized charge transfer efficiency and pronounced degree of charge separation. Our findings provide actionable insights for the rational design of high-performance organic Nonlinear optics (NLO) materials with potential applications in advanced photonic devices.