Exploring Excited State Proton Transfer in Thin Films Under Vibrational Strong Coupling

Abstract

Abstract Molecular structure, solvent/matrix, the surrounding environment, and molecular vibrations can influence the excited‐state proton transfer (ESPT) process. Theoretical studies predict that light‐matter strong coupling can modify the energy barrier for proton transfer reactions. Here, we experimentally explore the role of vibrational strong coupling (VSC) on the ESPT using the weak photoacid, 7‐hydroxy‐1‐naphthalenesulfonate (N8S) as the probe. The ESPT in N8S can occur through a solvent/matrix bridge connecting the proton‐donating and accepting units. To check the role of VSC, we embedded N8S in a poly(vinyl alcohol) (PVA) matrix and strongly coupled the ─OH stretching vibrational modes of PVA. The steady‐state and time‐resolved emission analysis reveal that the quantum yield of RO − emission and the ESPT rate constant enhance by a factor of two under VSC, compared to the noncavity, half‐cavity, and off‐resonance films. Our findings indicate that VSC can be a tool to control the proton transfer processes, opening avenues for developing physically tunable photoacid‐based sensors.