We demonstrate the control of excited state intramolecular proton transfer (ESIPT) of an organic molecule via strong coupling of the excited state to microcavity photons. Schematic of the microcavity structure consisting of Aluminum mirrors with alumina spacers and PMMA doped with the molecule (HMPP) is shown in Fig. 1a. HMPP is a potential candidate to show ESIPT in the solid-state. The absorption spectrum of the bare molecule along with the modified absorption under strong coupling is shown in Fig. 1b. Absorption of HMPP at 350 nm corresponds to the enol absorption; however enol state is intrinsically non-emissive. The absorption in the cavity shows two distinct peaks corresponding to the upper (300 nm) and lower (400 nm) polariton branches. Shown in Fig. 1c is the dispersion of the polaritons branches as a function of angle (corresponds to in-plane momentum) for cavities with different concentration of the HMPP molecule. Large Rabi splitting of ~ 1eV corresponding to the ultrastrong coupling regime is observed for the high concentration samples. In contrast the very low concentration (0.2 mg/mL) shows only weak coupling. The Stoke shifted emission of HMPP is due to the emission from the keto state after undergoing ESIPT. In the strong coupling regime we observe suppression of ESIPT resulting in lower emission from the keto state. In contrast, Purcell enhancement of emission was observed for the weakly coupled cavity. In summary we have shown the modification of ESIPT under strong light matter coupling in an optical cavity using an archetype molecular system: HMPP.

Excited state proton transfer under electronic light-matter strong coupling

256th National Meeting (2018)

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