Intermolecular Electronic Interactions: Alternative Paths for Photochemistry

6b7c192e-7d0d-4133-a5dc-e92b2cc282f5

Active

EPSRC
EPSRC
EPSRC
EPSRC
EPSRC

£2,193,810

Sept. 30, 2023

Sept. 30, 2026

Light-driven chemistry offers a new tool for chemical synthesis, renewable energy and photonics technologies. In chemical synthesis, the use of photochemical reactions as opposed to more traditional thermally-driven chemistry offers less energy-intensive reaction conditions but also the possibility to form otherwise inaccessible products. For a photochemical reaction or photoredox process to occur, there must be an intermolecular electronic interaction between the light-absorbing species and reactant to facilitate the energy transfer. Traditional fundamental photochemical studies have focused on understanding the photophysical reaction pathways in single, isolated molecules, rather than on the multispecies energy transfer processes necessary in photochemical synthesis and photoredox catalysis. For multispecies photochemical reactions, the strength and nature of these intermolecular interactions between reactive species and how they evolve in time are key to the photoinduced reactivity of the molecule and the reaction outcome. I have developed a number of spectroscopic tools and analysis methods over the years to understand the optical and geometric properties of a molecule and its resultant photophysics. Now, I will apply the spectroscopic tools I have developed to studying what types of intermolecular electronic interactions are present in a series of host-guest complexes. The understanding gained from these experiments will allow us to better understand the mechanisms involved in intermolecular electronic interactions and how to intentionally design new molecular candidates for light-driven applications. Our current knowledge of how intermolecular interactions work is largely limited to phenomenological models. Understanding the electronic and nuclear contributions to intermolecular electronic interactions from both the molecule and its environments is highly complex and necessitates the use of multiple cutting-edge spectroscopic methods.

Given the potential to enhance photoinduced reaction outcomes for improving the yields and efficiency of photochemical synthesis, this work proposes to develop the necessary fundamental understanding of intermolecular interactions through the use of specially-designed host-guest complexes and ultrafast optical and X-ray spectroscopies. The proposed families of host systems will include metal-organic cages (MOCs), a molecular equivalent of metal-organic frameworks, that form discrete monodisperse units in solution and are capable of housing guests as large as proteins, and organic macrocycles such as cucurbit[n]urils. In this work, the host complexes will provide a means of controlling the environment around the guest molecules and by changing the chemical composition of the host and the internal cavity size, a way of tuning the contribution of different electronic and nuclear contributions to the intermolecular electronic interactions. Actively involving the host complex in photoinduced reactions by direct excitation of the host itself as a way of triggering new photochemistry will also be explored.

The chosen families of spectroscopic methods, ultrafast optical and X-ray, are key to achieving the main objectives in this work. Optical spectroscopies provide the sensitivity to the global electronic structure and valence electronic states that are crucial in most optical applications. In complement to this, X-ray spectroscopies are highly site and element selective and can provide the structural information that is challenging to capture from optical methodologies alone. Through characterisation of the photophysics of the individual host and guest and what alterations occur on formation on the host-guest complex it will be possible to explore practical routes to influencing the outcome of photochemical reactions as well as the fundamentals and nature of the host-guest interactions.