This paper is part of a special issue dedicated to Professor J. C. (Tito) Scaiano on the occasion of his 60th birthday.
A Photodissociation Reaction: Experimental and Computational Study of 2-Hydroxy-2,2-dimethylacetophenone†
Article first published online: 30 APR 2007
Photochemistry and Photobiology
Volume 82, Issue 1, pages 88–94, January 2006
How to Cite
Allonas, X., Morlet-Savary, F., Lalevée, J. and Fouassier, J.-P. (2006), A Photodissociation Reaction: Experimental and Computational Study of 2-Hydroxy-2,2-dimethylacetophenone. Photochemistry and Photobiology, 82: 88–94. doi: 10.1562/2005-05-20-RA-535
- Issue published online: 30 APR 2007
- Article first published online: 30 APR 2007
- Received 20 May 2005; accepted 10 August 2005; published online 12 August 2005
The photophysical parameters controlling the cleavage process of 2-hydroxy-2,2-dimethylacetophenone (HDMA) were investigated in detail. Time-resolved picosecond absorption experiments show that the formation of the triplet state occurs within 20 ps after excitation and decays within hundreds of picoseconds depending on the solvent polarity. Molecular modeling reveals that three stable conformations exist in the ground state, the most stable one exhibiting an intramolecular hydrogen bond that modifies the electronic properties of the molecule. This explains quite well the steady-state absorption properties. The conformation of the most stable triplet state is twisted by 180° with respect to the ground state. Computation of the potential energy surface along the molecular coordinate for the dissociation reaction evidences an electronic state crossing yielding a final σσ* state, in perfect agreement with the state correlation diagram. Optimization of the transition state allows the calculation of the activation energy and the use of the transition-state theory leads to an estimate of 100 ps for the cleavage process in the gas phase. Single-point energy calculations using a solvent model predict an increase of the dissociation rate constant with the increase of the solvent polarity, in good agreement with the value deduced from kinetic measurements.