Elucidating Halogen-Assisted Self-Assembly Enhanced Mechanochromic Aggregation-Induced Emission

Abstract

We present a successful strategy to obtain a self-assembled material stabilized by halogen bonding with enhanced mechanochromic aggregation-induced emission (AIE). The meta-bromophenyl-substituted tetraphenylethene fluorophore (m-BrTBE) exhibits an emission which is more red-shifted compared to the phenyl-ring-substituted tetraphenylethene fluorophore (TBE) in film. Remarkably, m-BrTBE molecules self-assemble into uniform ball-like aggregates with high photoluminescence quantum yield up to 85.3 %, which indicates that the molecular conformation and intermolecular interactions are different from those in the crystalline state. Based on single-crystal analysis, scanning tunneling microscopic observations, and theoretical calculations, the unusual self-assembly enhanced AIE behavior is attributed to the important effect of meta-bromide substituents which not only form intermolecular Br⋅⋅⋅π halogen bonding and H⋅⋅⋅Br hydrogen bonding interactions to block nonradiative relaxation pathways effectively but also promote radiative processes.