Concurrent Enhancement of Aggregation-induced Emission and Two-photon Absorption in Symmetric Naphthalimide Derivatives via Methoxy Substitution.

In this work, bisNAPTPA and its derivative bisNAPTPA-OCH3 have been investigated to reveal how targeted methoxy substitution tunes the photophysical properties in symmetric naphthalimide derivatives. Combined experimental and theoretical analyses reveal that the introduced methoxy groups at the terminals of triphenylamine groups not only induce distinct aggregation-induced emission (AIE) by restricting intramolecular motions, as confirmed by time-resolved fluorescence, but also significantly enhance intramolecular charge transfer (CT). This enhanced intramolecular CT characteristic leads to a red shift in absorption and a notable improvement in the two-photon absorption (TPA) cross-section. Visualization of excited states via transition density matrix and charge density difference analyses provides a mechanistic understanding of the superior electron delocalization and nonlinear optical response in bisNAPTPA-OCH3. Our findings suggest that methoxy functionalization represents a promising molecular design motif for simultaneously enhancing AIE characteristics and TPA performance in symmetric naphthalimide derivatives.