Aggregation induced emission and mechanofluorochromic properties of tetraphenylethylene-based luminogen: Fluorescence enhancement induced by phase transition

The construction of solid-state fluorescent materials with high quantum yield is of vital importance in the preparation of organic light-emitting devices. A tetraphenylethylene-based (TPE) derivative with aldehyde and phenacetylene groups is synthesized (ETPPE) showing obvious AIE behavior and its photophysical properties in powder, ground and film states are investigated. Impressively, ETPPE displays tunable mechanofluorochromic property under external mechanical stimulation, and exhibits excellent fluorescence quantum yield (ΦF = 88.1 %). Based on single-crystal analysis, scanning tunneling microscopic observation, and theoretical calculations, the enhanced AIE behavior is attributed to different hydrogen bonds in the amorphous state by changing the molecular packing mode and spatial conformation. Both the terminal aldehyde groups and the phenyl rings in the TPE cores of ETPPE molecules are involved in the formation of various hydrogen bonds in the crystalline state. A 2D self-assembled adlayer is constructed on the highly oriented pyrolytic graphite (HOPG) surface, and the intermolecular hydrogen bonds only formed between the terminal aldehyde groups participate in the linear nanostructure. The results reveal that the different molecular packing modes and spatial conformations caused by the phase transition are the dominant factors leading to the emission enhancement, which opens a feasible route to reveal the relationship between the structure and the property from the systematic molecular scale point of view.