Photochemically Removable Protecting Groups Based on Covalently Linked Electron Donor−Acceptor Systems

Abstract

Photoremovable protecting groups based on intramolecular electron transfer have been synthesized and studied. One molecule contains a N,N-dimethylaniline chromophore covalently linked to a phenacyl ester of acetic acid. UV photolysis of this molecule results in the release of acetic acid. Laser flash photolysis experiments show that photolysis creates an intramolecular charge-transfer state that has a lifetime of approximately 500 ns. This charge-transfer state partitions between a bond scission pathway leading to elimination of acetic acid and a charge-recombination pathway leading back to ground-state reactants. An analogous system, using an anthracene chromophore, was also synthesized. This did not release the carboxylic acid upon UV photolysis. Instead, laser flash photolysis experiments showed rapid formation of an anthracene-localized triplet excited state.