Room Temperature Proton Coupled Energy Transfer

Proton-coupled energy transfer (PCEnT) is new ¹ and differs from traditional energy transfer in that there is virtually no ground-state tautomer population, but energy transfer can still occur by simultaneously coupling the proton transfer. PCEnT should herald a revolutionary photochemical breakthrough. However, despite theoretical advancement ² , so far, the only PCEnT-related experiment was performed under an extreme environment (77K glass matrix) with complexity ¹ . Herein, utilizing a new molecular triad AbPP comprising anthracene and bridged phenolpyridine, we provide direct and unambiguous experimental evidence for PCEnT in the room temperature solution for the first time. In cyclohexane, the rate of PCEnT for AbPP is measured to be (125 ps) ^-1 , which is three orders of magnitude slower than the rate of direct excited-state intramolecular proton transfer (ESIPT)((176 fs) ^-1 ) but yields the same 645 nm proton transfer isomer emission, supporting a weak nonadiabatic coupling process for PCEnT. This result challenges the traditional assumption that quantum processes manifest primarily at low temperatures, as it demonstrates that PCEnT—a fundamentally quantum mechanical mechanism—can occur efficiently in room-temperature solutions. Equally important, the resolved emission of proton-transfer tautomers and charge-separated states produced by PCEnT and proton-coupled electron transfer (PCET), respectively, allows for comprehensive probing of the correlation between PCEnT and PCET, with the increase of PCET rates upon increasing solvent polarity. These findings diversify the interplay among electron, proton, and energy transfer, the three fundamental mechanisms of chemical transformations.