Enhancing Fluorescence in Both Solution and Solid States Induced by Imine Cage Formation

Developing luminescent materials that exhibit strong emissions in both solution and solid phases is highly desirable and challenging. Herein, we report imine-bond directed formation of a rigid organic cage (TPE-cage) that was synthesized by [2+ 4] imine condensation of a TPE-cored tetra-aldehyde (TPE-TA) with a clip-like diamine (XA) to illustrate confinement-induced fluorescence enhancement. Compared to the non-emissive TPETA (phi(F)= 0.26%) in the dichloromethane (DCM) solution, the TPE-cage achieved a remarkable (similar to 520-fold) emission enhancement (phi(F)= 70.38 %). In contrast, a monomeric tetra- imine model compound (TPE-model) showed only a minor enhancement (phi(F)= 0.56%) in emission compared to the parent tetra-aldehyde TPE-TA. The emission of TPE-cage was further enhanced by similar to 1.5-fold (phi(F)= 80.96%) in the aggregated state owing to aggregation-induced emission enhancement (AIEE). This approach establishes the potential for synthesizing luminescent materials with high emission in both solution and solid-state by employing a single-step imine condensation reaction.