On the Role of Symmetry in Vibrational Strong Coupling: The Case of Charge‐Transfer Complexation

Abstract

It is well known that symmetry plays a key role in chemical reactivity. Here we explore its role in vibrational strong coupling (VSC) for a charge‐transfer (CT) complexation reaction. By studying the trimethylated‐benzene–I2 CT complex, we find that VSC induces large changes in the equilibrium constant KDA of the CT complex, reflecting modifications in the ΔG° value of the reaction. Furthermore, by tuning the microfluidic cavity modes to the different IR vibrations of the trimethylated benzene, ΔG° either increases or decreases depending only on the symmetry of the normal mode that is coupled. This result reveals the critical role of symmetry in VSC and, in turn, provides an explanation for why the magnitude of chemical changes induced by VSC are much greater than the Rabi splitting, that is, the energy perturbation caused by VSC. These findings further confirm that VSC is powerful and versatile tool for the molecular sciences.

Chemistry under Vibrational Strong Coupling

“…[117][118][119] In order to test whether symmetry is also an important ingredient in VSC, a wellknown charge transfer (CT) equilibrium reaction between mesitylene and iodine was chosen. 77 By coupling the vibrational modes of mesitylene with different symmetry, the equilibrium constant K DA of the CT complex was studied and it was found that K DA was increased or decreased depending on the symmetry of the molecular vibration being coupled but independent of the coupling frequency and the type of vibration. 77 Similar result was observed in a charge transfer complexation between benzene and iodine under VSC.…”

Challenges in Plasmonic Catalysis

“…154 Experiments in strong-coupling chemistry have presented the intriguing possibility of changing chemical reactions or controlling their selectivity. [155][156][157][158][159] Combining approaches from diverse fields presents an opportunity to create a predictive theoretical and computational approach to describe cavity-correlated chemical dynamics from first principles. 154,160 Many key theoretical challenges remain.…”

Excited-state vibration-polariton transitions and dynamics in nitroprusside

“…Strong coupling between infrared-active vibrational modes and photonic cavities offers the unique possibility of systematic modification of the vibrational energy landscape of a molecular system and specific bond activation/deactivation. This has been demonstrated with reduced bond cleavage rates 13 , enhanced enzymatic activity 14 , charge transfer equilibria 15 , and modified product branching ratios 16 . Key to these processes, we believe, are the hybrid light–matter polariton states formed under strong coupling conditions 17 .…”