Probing the dynamics of small anions in optical cavities

Coupling vibrational modes to optical cavities offers a method to systematically and predictably modify the vibrational energy landscape of a molecule. A confined optical mode can couple to a resonant material transition and lead to enhanced absorption/emission rates, excited state population control, and the formation of new hybrid states. There is a rich history of coupling to electronic transitions, including quantum wells and J-aggregates, coupling to vibrational transitions has only been explored recently. We reported time resolved IR studies on strongly coupled vibration-cavity polaritons for W(CO)₆ in hexane. The result demonstrated that much of the response is due to uncoupled reservoir excited state absorption and there is evidence for an angle-tuning dependent decay time for the upper polariton (UP) to v = 2 transition. We have explored other solutes with shorter dephasing times vibration-cavity systems. Dicyanamide and thiocyanate have strong mid-IR absorptions and are capable of strong coupling to optical fields. However, in both anions, we do not observe the UP to v = 2 transition that was observed in the W(CO)₆ cavity. The results are discussed in terms of how they impact the prospects for observing polariton relaxation effects in vibration-cavity systems.