Cavity Catalysis: Modifying Linear Free-energy Relationship under Cooperative Vibrational Strong Coupling

Abstract

Recent understanding of light-matter strong coupling brought a new niche in molecular-level control of chemical reactions. Vibrational strong coupling is unique in this category that overcomes the issue associated with coherent chemistry. Here, a vibrational transition is coupled to a standing wave of electromagnetic field, result in strong interaction, generating vibro-polaritonic states. This process reshuffles the entire energy-reaction coordinate. The chemical reaction rate can be boosted, stirred, or decelerated with this unconventional tool. Here, we used the idea of cooperative vibrational strong coupling of solute and solvent molecules to enhance the chemical reaction rate. This process is called cavity catalysis. Different derivatives of p-nitrophenyl benzoate (solute) and isopropyl acetate (solvent) are cooperatively coupled to an infrared Fabry-Perot cavity. The apparent reaction rates are increased by more than six times at the ON resonance condition, and the rate enhancement follows the lineshape of the vibrational envelope. Very interestingly, strong coupled system doesn't follow a linear free-energy relationship. The nonlinear rate enhancement can be due to the reshuffling of energy distribution between the substituents and the reaction center. Thermodynamic parameters suggest an entropy-driven process for the coupled molecules. The free energy of activation decreased by 2-5 kJ/mol, suggesting a clear role of vibrational strong coupling in catalyzing the reaction. Here, the enthalpy of the system compensates for the entropy by preserving the isokinetic relationship. These findings will help further understanding of chemical reaction control in polariton chemistry. TOC

Molecular orbital theory in cavity QED environments

“…This idea was also reported by Galego et al 16 and tested using a transition state method for the strong light-matter coupling case. Strong coupling between molecular vibrations and cavity fields, vibrational strong coupling (VSC), has proven to be a particularly effective way to affect the outcome of molecular reactions 14,17,18,47 . Although the number of experiments displaying to what extent reactions can be engineered through VSC is constantly increasing, several aspects still remain unclear.…”

Chemistry under Vibrational Strong Coupling

“…Recently six other para-nitrophenyl benzoate (PNPB) derivatives under cooperative VSC have been reported showing enhanced solvolysis rates and interestingly, the linear free energy relationship is modified under strong coupling. 88 Enzymatic activity under VSC has been reported in two different studies. 61,86 In one case the activity of protease pepsin was studied under VSC of water molecules.…”

“…49, 61-63, 76-77, 85-88 The possibility of coupling the reactants indirectly through their overlap with the vibrational modes of surrounding molecules (such as the matrix or the solvent), the so-called cooperative strong coupling, opens up new possibilities to modify material properties when direct coupling is not possible as explained further down. 62,65,72,88,96,100 Many theoretical groups are working on this field to understand why VSC leads to such large changes in experimental observations and not surprisingly, symmetry is a fundamental factor. This perspective introduces fundamental concepts before highlighting the recent advancements of VSC to alter the chemical reactivity and molecular processes.…”