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1. Collective Vibrational Strong Coupling Effects on Molecular Vibrational Relaxation and Energy Transfer: Numerical Insights via Cavity Molecular Dynamics Simulations

   Li, T.E. Li; Nitzan, A.; Subotnik, J.E. (May 2021, Angewandte Chemie)

   null (Ed.)

   We use classical cavity molecular dynamics simulations to investigate the effect of optical cavity environment on vibrational energy transfer and relaxation. For a small fraction of vibrationally hot CO2 molecules immersed in a liquid-phase CO2 thermal bath, in a cavity that supports a cavity mode in resonance with the CO asymmetric stretch vibration, forming collective vibrational strong coupling (VSC) and a cavity mode accelerates hot molecule relaxation. This acceleration stems from the fact that polaritons can be transiently excited during the nonequilibrium process, which facilitates intermolecular vibrational energy transfer. The VSC effects on these rates (i) resonantly depend on the cavity mode detuning, (ii) cooperatively depend on Rabi splitting, and (iii) collectively scale with the number of hot molecules. This behavior weakens with increasing cavity size (at constant molecular density), that is, constant Rabi splitting) but remains meaningful up to cavities containing 10^4 molecules 

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2. A molecular T-pentomino for separating BTEX hydrocarbons

   https://doi.org/10.1038/s41467-024-45542-2  

   Hartwick, Christopher J.; Reinheimer, Eric W.; MacGillivray, Leonard R. (March 2024, Nature Communications)

   Abstract Methods to separate molecules (e.g., petrochemicals) are exceedingly important industrially. A common approach for separations is to crystallize a host molecule that either provides an enforced covalent cavity (intrinsic cavity) or packs inefficiently (extrinsic cavity). Here we report a self-assembled molecule with a shape highly biased to completely enclose space and, thereby, pack efficiently yet hosts and allows for the separation of BTEX hydrocarbons (i.e., benzene, toluene, ethylbenzene, xylenes). The host is held together by N → B bonds and forms a diboron assembly with a shape that conforms to a T-shaped pentomino. A T-pentomino is a polyomino, which is a plane figure that tiles a plane without cavities and holes, and we show the molecule to crystallize into one of six polymorphic structures for T-pentomino tiling. The separations occur at mild conditions while rejecting similarly shaped aromatics such as xylene isomers, thiophene, and styrene. Our observation on the structure and tiling of the molecular T-pentomino allows us to develop a theory on how novel synthetic molecules that mimic the structures and packing of polyominoes can be synthesized and—quite counterintuitively—developed into a system of hosts with cavities used for selective and useful separations. 

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3. Cavity frequency-dependent theory for vibrational polariton chemistry

   https://doi.org/10.1038/s41467-021-21610-9  

   Li, Xinyang; Mandal, Arkajit; Huo, Pengfei (February 2021, Nature Communications)

   Abstract Recent experiments demonstrate the control of chemical reactivities by coupling molecules inside an optical microcavity. In contrast, transition state theory predicts no change of the reaction barrier height during this process. Here, we present a theoretical explanation of the cavity modification of the ground state reactivity in the vibrational strong coupling (VSC) regime in polariton chemistry. Our theoretical results suggest that the VSC kinetics modification is originated from the non-Markovian dynamics of the cavity radiation mode that couples to the molecule, leading to the dynamical caging effect of the reaction coordinate and the suppression of reaction rate constant for a specific range of photon frequency close to the barrier frequency. We use a simple analytical non-Markovian rate theory to describe a single molecular system coupled to a cavity mode. We demonstrate the accuracy of the rate theory by performing direct numerical calculations of the transmission coefficients with the same model of the molecule-cavity hybrid system. Our simulations and analytical theory provide a plausible explanation of the photon frequency dependent modification of the chemical reactivities in the VSC polariton chemistry. 

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4. Customizable molecular recognition: advancements in design, synthesis, and application of molecularly imprinted polymers

   https://doi.org/10.1039/D1PY01472B  

   Reville, Erinn K.; Sylvester, Elizabeth H.; Benware, Sarah J.; Negi, Shreeya S.; Berda, Erik B. (June 2022, Polymer Chemistry)

   Molecularly imprinted polymers (MIPs) are where the complexity of receptor proteins meets the tunability of synthetic research. Receptor proteins, such as enzymes or antibodies, have functional cavities that act as docking platforms by recognizing and binding to complementary ligands. Once bound, a receptor–ligand complex may generate any multitude of cellular responses, including the regulation, uptake, and/or release of certain hormones, neurotransmitters, inorganic minerals, antigens, enzymes, and other molecules within an organism. Just like receptor proteins, MIPs are polymers with carefully selected functional groups that are spacially arranged to recognize target molecules. MIPs are generated by templating a functionalized polymer with a molecule, leaving a cavity that is complementary to the molecule upon removal. That cavity then has an affinity for the molecule that was templeted for later rebinding. The aim of MIP research is to recognize a desired target molecule with the precision of receptor proteins, and to maintain specificity and sensitivity towards the target molecule while tailoring functional properties for advanced applications. Resarchers are far from perfecting the delicate intricacy of mimicking such elegant biological processes, and improvements in all areas of MIP synthesis remain a vibrant and active topic. Various methods explored to synthesize MIPs with impressive recognition capabilities towards target molecules and the recent applications of MIPs are found herein. This review aims to dissect the synthetic steps required to generate MIPs, with emphasis on the more recent routes utilized and overall application advances. 

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5. Resonance theory of vibrational polariton chemistry at the normal incidence

   https://doi.org/10.1515/nanoph-2023-0685  

   Ying, Wenxiang; Taylor, Michael A.; Huo, Pengfei (February 2024, Nanophotonics)

   Abstract We present a theory that explains the resonance effect of the vibrational strong coupling (VSC) modified reaction rate constant at the normal incidence of a Fabry–Pérot (FP) cavity. This analytic theory is based on a mechanistic hypothesis that cavity modes promote the transition from the ground state to the vibrational excited state of the reactant, which is the rate-limiting step of the reaction. This mechanism for a single molecule coupled to a single-mode cavity has been confirmed by numerically exact simulations in our recent work in [J. Chem. Phys. 159, 084104 (2023)]. Using Fermi’s golden rule (FGR), we formulate this rate constant for many molecules coupled to many cavity modes inside a FP microcavity. The theory provides a possible explanation for the resonance condition of the observed VSC effect and a plausible explanation of why only at the normal incident angle there is the resonance effect, whereas, for an oblique incidence, there is no apparent VSC effect for the rate constant even though both cases generate Rabi splitting and forming polariton states. On the other hand, the current theory cannot explain the collective effect when a large number of molecules are collectively coupled to the cavity, and future work is required to build a complete microscopic theory to explain all observed phenomena in VSC. 

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