Isotope Engineering in Tetraphenylethylene: Aggregate-Dependent Photophysical Enhancements

Aggregation-induced emission (AIE) luminogens, exemplified by tetraphenylethylene (TPE), exhibit enhanced fluorescence in aggregated states and have promising applications in display, photodetectors, fluorescent probes, bioimaging, and biomedicine. This study investigates the influence of varying degrees of deuteration on the photophysical properties of TPE across different aggregation states. Through the synthesis of partially and fully deuterated TPE derivatives (TPE-5d, TPE-10d, TPE-20d), combined with steady-state fluorescence spectroscopy, time-resolved fluorescence measurements, transient absorption spectroscopy, and density functional theory (DFT) calculations, we elucidate the dual role of deuteration in modulating non-radiative decay pathways. In loosely packed nanoaggregates, increased deuteration enhances photoluminescence quantum yields (PLQY) and extends fluorescence lifetimes by reducing internal conversion rates. Conversely, in tightly packed crystalline states, deuteration leads to decreased PLQY and shortened lifetimes, attributable to the Duschinsky rotation effect (DRE), which enhances inter-mode coupling and internal conversion. Additionally, deuteration significantly prolongs the operational lifetime of blue organic light-emitting diode (OLED) devices, decuplicating the device lifespan in deuterated TPE-20d compared to non-deuterated TPE. This work underscores the necessity of evaluating structure-property relationships at the aggregate level, rather than solely at the molecular level, to fully comprehend and optimize AIE phenomena. These findings highlight the potential of isotope engineering in designing durable and efficient AIE luminogens for applications in optoelectronics and bioimaging.