Dendritic polyphenylene AIEgens: fluorescence detection of explosives and stimulus-responsive luminescence

Abstract

Luminescent dendrimers have proved their great potential as promising emitting materials toward application in displays, imaging and sensing. Herein, a series of dendritic luminogens with a tetraphenylethene (TPE) unit as the core and oligophenylene moieties as the dendrons with diverse peripheries have been synthesized. Due to the semi-rigid and giant dendritic architecture, the emission quantum yields of these dendrimers are obviously increased; however, aggregation-induced emission (AIE) properties are still retained. The influence of peripherals on the luminescence sensing process has been carefully investigated. Dendritic AIEgens could detect picric acid via dynamic quenching involving both electron transfer and energy transfer processes, whereas electron-rich peripherals would promote this. In addition, the photostability and resistance to exterior environmental stimuli of these dendritic AIEgens were further evaluated as aggregates or solids. Furthermore, the emission of these AIEgens exhibited an obvious response to external stimuli, including light, mechanical force and volatile organic vapour. This stimulus-responsive luminescence was closely related to the steric effect of peripheries, which would influence the intramolecular packing of dendritic AIEgens in the solid state. Dendrimers with more bulky peripheries provided larger interior voids for central TPE units in the solid state, and consequently facilitated their reorganization into photocyclized intermediates. On the other hand, dendrimers with less bulky peripheries have the tendency to crystalize with denser packing and were susceptible to the transformation between crystalized and amorphous phases, which resulted in pronounced luminescence response to exterior stimuli.