The international research team has made a significant discovery about the behavior of 8-hydroxypyrene-1,3,6-trisulfonate (HPTS), a fluorescent probe extensively used for studying proton transfer and local pH in diverse systems. Contrary to the prevailing view of molecular probes as static reporters, the study reveals that HPTS exhibits dynamic behavior when nanoconfined within anionic AOT reverse micelles.
Using steady-state and time-resolved optical spectroscopy, molecular simulations, and IR solvation shell spectroscopy, the researchers found that HPTS’s protonated form strongly associates with the micelle interface through hydrogen bonding. In contrast, its deprotonated form resides in the micelle’s aqueous interior. Upon photoexcitation, the protonated HPTS deprotonates, and the resulting conjugate base rapidly moves away from the interface into the water pool. This light-induced translocation was observed across a range of micelle sizes.
The findings challenge the traditional assumption that molecular probes remain static within their environments, providing a more nuanced understanding of their behavior. This dynamic translocation suggests that probes like HPTS can act as explorers, capable of mapping environmental heterogeneity on the timescale of the processes they are designed to measure.
The discovery is particularly relevant for interpreting results in numerous studies that employ HPTS to investigate complex systems, from advanced materials to plants and from environmental sensors to medicine. This new perspective could lead to more accurate interpretations and a deeper understanding of the systems being studied.
The study was published in Proceedings of the National Academy of Sciences.