Molecular Materials with Contrasting Optical Responses from a Single-Pot Reaction and Fluorescence Switching in a Carbon Acid

摘要

A wide variety of amines are known to react with 7,7,8,8-tetracyanoquinodimethane (TCNQ) to yield pushCpull diaminodicyanoquinodimethanes with a strongly zwitterionic structure and significant optical and nonlinear optical properties. A novel course of reaction is observed now with the amine 2-methyl-4-chloroaniline, which leads to three well-defined products, ACC, in a single pot. A and B are formed through the replacement of one cyano group in TCNQ by the amine; A is a carbon acid and B is its corresponding salt. C is the conventional product in which two cyano groups in TCNQ are replaced by the amine.The products are characterized structurally and spectroscopic studies reveal contrasting optical responses. A is nonfluorescent, whereas B and C show red and green emission, respectively, in the solution and solid states. The acid/conjugate-base pair A and B can be interconverted through facile, reversible,and repeated deprotonation/protonation cycles, which are accompanied by instantaneous switching of the fluorescence.The current study illustrates an interesting case of a single-pot reaction yielding different optical materials with attributes that can be switched through simple approaches such as protonation or tuned through modification of the pushCpull characteristics.