Peresters and use thereof

Compound of the formula:

• ##STR16## wherein R is a C.sub.1 -C.sub.22 alkyl group;
• and R.sub.1 is an organic group such that the moiety ##STR17## is a light absorbing chromophore group which produces an excited state by light absorption and is selected from the group consisting of C.sub.1 -C.sub.22 alkyl groups, C.sub.3 -C.sub.22 cycloalkyl groups, C.sub.6 -C.sub.22 aryl groups, C.sub.7 -C.sub.22 aralkyl groups, C.sub.7 -C.sub.22 alkaryl groups, C.sub.1 -C.sub.22 alkoxy substituted aryl groups and morpholinyl, piperidyl, thiophenyl and furanyl heterocyclic groups.