Chemistry, Light and Dynamics Group Seminar

The properties of a solvent can have pronounced effects on the pathways and outcomes of photochemical reactions, with consequences for light-activated chemical synthesis and catalysis.¹  At a microscopic level, solute-solvent interactions modify the energies of excited electronic states and their crossings, leading to changes in the photochemical dynamics.²  These effects can be explored using ultrafast transient absorption spectroscopy in the UV-visible and mid-IR regions, supported by electronic structure calculations of excited-state reaction pathways.     

Several recent investigations from our laboratory have examined the effects of the surrounding solution on the ultrafast photochemical dynamics of organic chromophores.   Examples include mechanisms of UV protection in the sunscreen molecule diethylamino hydroxybenzoyl hexyl benzoate,³ and competition between heterocyclic ring-opening and N-H bond fission pathways in 2-aminothiazole.⁴  The results illustrate how polar, non-polar or protic solvent interactions with excited state organic chromophores can shift the balance between competing, non-adiabatic photochemical pathways.  Such studies offer prospects for a better understanding of how different solvents affect the outcomes and yields of photochemical reactions used in chemical synthesis.    

1.  Singlet and triplet excited state contributions to the activity of dihydrophenazine, phenoxazine and phenothiazine organocatalysts employed in atom transfer radical polymerization, A. Bhattacherjee, M. Sneha, L. Lewis-Borrell, G. Amoruso, T.A.A. Oliver, J. Tyler, I.P. Clark, and A.J. Orr-Ewing, J. Am. Chem Soc. 2021, 143, 3613–3627.  

2 Intermolecular hydrogen bonding controlled intersystem crossing rates of benzophenone, R.K. Venkatraman, S. Kayal, A. Barak, A.J. Orr-Ewing, and S. Umapathy, J. Phys. Chem. Lett. 2018, 9, 1642−1648. 

3.  Influence of the solvent environment on the ultrafast relaxation pathways of a sunscreen molecule diethylamino hydroxybenzoyl hexyl benzoate, M.H. Kao, R.K. Venkatraman, M. Sneha, M. Wilton, and A.J. Orr-Ewing, J. Phys. Chem. A, 2021, 125, 636–645. 

4.  Ryan Phelps, Ph.D. Thesis, University of Bristol, 2021