Photocyclisation of 2-pyridyl phenyl ketone. A reaction driven by hydrogen bonding

Abstract

The photochemistry of 2-pyridyl phenyl ketone (2-PPK) has been studied in water, ethanol and other organic solvents of different polarity and hydrogen-bonding ability. Steady-state and laser flash photolysis (ps and ns resolution) techniques were used to determine the photoproducts and the reaction intermediates. The reactive state is the lowest n,π* carbonyl triplet. Three different photoreaction paths were recognised leading to cyclisation and reduction products. The relative contribution to the overall reaction by the different pathways is governed by the hydrogen-bonding ability of the solvent.