High-Pressure Spectroscopic Probing of Aggregation-Dependent Luminescence in Tetraphenylethylene: Deciphering Intra- vs Intermolecular Interactions

Tetraphenylethylene (TPE), a prototypical aggregation-induced emission luminogen (AIEgen), has been systematically investigated via combined experimental methods to elucidate its emission and conformational evolution under high pressure. The photoluminescence modulation is governed by the competitive interplay between intramolecular C-H···π and intermolecular π-π interactions. Using argon as a pressure-transmitting medium (PTM), fluorescence quenching occurs below 1.4 GPa as a result of changes in the intramolecular C-H···π and C-H···C hydrogen-bonding interactions, which promote nonradiative decay pathways. Conversely, between 1.4 and 4.9 GPa, restricted intramolecular rotation (RIR) induced by intermolecular interactions amplifies luminescence intensity by 8-fold. Besides that, molecular planarization initiates at 4.9 GPa, extending π-conjugation and causing a fluorescence red shift alongside abrupt emission quenching. Furthermore, the molecular planarity of TPE contributes to the enhancement of intermolecular π-π interactions, along with promoting π-orbital overlap and inducing intermolecular coupling─factors that constitute the primary cause of fluorescence quenching under pressures exceeding 12 GPa. Notably, the pressure points corresponding to the fluorescence change have changed when water serves as the PTM. The aqueous environment significantly retards key phase transitions by mediating C-H···O/O-H···π hydrogen-bonding networks orthogonal to π-stacking configurations. These results establish explicit correlations between molecular dynamics and optoelectronic responses, resolving prior contradictions in TPE's pressure-dependent behavior and providing a design framework for stimuli-responsive AIE materials.