Strain Energy Prompted Tunable Aggregation-Induced Emission Property of Tetraphenylethylene

Organic molecules exhibiting aggregation-induced emission (AIE) have attracted considerable attention due to their exceptional solid-state luminescent properties. Understanding the AIE mechanism has been a focal point of both theoretical and experimental research. While conical intersection (CI) dynamics on potential energy surfaces (PESs) have emerged as a key factor in elucidating the AIE mechanism, modulating the accessibility to CI to regulate the non-radiative decay pathways remains a substantial challenge. Here we propose a new strategy leveraging strain energy introduced by cycloparaphenylenes (CPPs) to tune the AIE property of tetraphenylethylene (TPE). We synthesized and characterized a series of TPE-incorporated CPPs with varying sizes and endo/exo vinyl moieties. The photophysical properties and AIE behavior of these strained TPE-CPPs were meticulously examined. Endo-TPE-CPPs exhibit AIE, while Exo-TPE-CPPs do not, opposite to strain-free TPE macrocycles. The luminescence of Endo-TPE-CPPs and Exo-TPE-CPPs can be further tuned by adjusting the number of phenylene units in the loop. Their excited-state dynamics were investigated using density functional theory (DFT) calculation and time-resolved absorption spectroscopy. The strain energy induces structural distortion of TPE, stabilizing or elevating the transition state (TS), thereby regulating the accessibility to CI and enabling tunable AIE properties. These findings provide new insights for designing AIE molecules.