Visible light-induced transformation of pendant acyloxyimino (AOI) and carbamoyloxyimino (COI) groups to basic groups was studied in the presence of triplet sensitizers. The quantum yields of photolysis at 405 nm for both AOI and COI groups decreased in the order isopropylthioxanthone (iPTX) > 7,7'-didecanoxy-3,3'-ketobiscoumarin (DKC) > 7.7'-bis(diethylamino)-3,3'-ketobiscoumarin (AKC). This order was in agreement with that of triplet energy levels of sensitizers. Steady-state phosphorescence quenching study using model compounds afforded the same results. These results indicated that the photoreactions were induced by energy transfer. The sensitized photoreaction was applied to the solubility changes of the films. The copolymer films bearing AOI groups became soluble in methanol on irradiation followed by HCI-treatment, and became insoluble in tetrahydrofuran (THF) on irradiation followed by post-exposure bake treatment. Films bearing COI groups became insoluble in THF due to crosslinking between aminyl radicals. (c) 2006 Elsevier B.V. All rights reserved.