1. A compound of formula EQU R.sub.1 --YArCOOOR wherein R is C.sub.1 -C.sub.22 alkyl; Ar is selected from the group consisting of phenyl, naphthyl, anthryl, pyryl, and phenanthryl; Y is selected from the group consisting of --CH.sub.2 --, C.dbd.O, and C.dbd.N; R.sub.1 is selected from the group of C.sub.1 -C.sub.22 alkyl, C.sub.3 -C.sub.22 cycloalkyl, C.sub.6 -C.sub.22 aryl, and C.sub.7 -C.sub.22 arylalkyl R.sub.1 absorbing radiation between 250 and 800 nm such that R.sub.1 is a light absorbing chromophore group that produces an excited state by light absorption; except that when Ar is phenyl, Y is not C.dbd.O and R.sub.1 is not C.sub.1 -C.sub.22 alkyl or C.sub.6 -C.sub.22 aryl.