Aggregation/Viscosity-Induced Emission and Third-Order Nonlinear Optical Signal Inversion in a TICT System

Abstract

Twisted intramolecular charge transfer (TICT) process endow the luminogens containing rotatable electron donor-π-acceptor (D-π-A) structure with abundant electronically excited states, resulting in multiple photophysical properties. In this work, a new propeller-like molecule of 5,6-di(4-N,N-(dimethylamino)phenyl)pyrido[2,3-b]pyrazine (APPP) with rotatable D-π-A structure was facilely prepared, which exhibited typical TICT character. Interestingly, aggregation/viscosity-induced emission and third-order nonlinear optical (NLO) signal inversion from reverse saturation absorption to saturation absorption in aggregated state or solutions with high viscosity were observed in this system. Mechanism study showed that these properties were originated from the restricted intramolecular rotation (RIR) process, which not only cut off the non-radiative transition channel of excited electron but also influenced the excited electron transition rate from charge transfer (CT) state to TICT state. According to these results, a temperature-triggered third-order NLO optical switch was successfully designed. This work affords a new type of aggregation-induced emission luminogen (AIEgen) with third-order NLO properties, and more importantly, provides a visualized prototype to understand the origination of third-order NLO properties in TICT systems.