Multifunctional O -Acyloximes as Near-UV- and Visible Light-Sensitive Photoinitiators

Abstract O-Acyloximes having multiple fused aromatic rings and ferrocene as chromophores were proposed as multifunctional photoinitiators sensitive to near-UV and visible light, and their photochemical properties and initiating ability in photocuring and photocrosslinking were investigated. In addition to already published truxenone O,O′,O″-tris(phenylacetyl)trioxime (TruxAO), 9,10-anthraquinone O,O′-bis(phenylacetyl)dioxime (AtqAO), 2,7-diacetylfluorene O,O′-bis(phenylacetyl)dioxime (FluAO), and 1,1′-diacetylferrocene O,O′-bis(phenylacetyl)dioxime (FerroAO) were newly prepared and compared with conventional diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) and 4,5-dimethoxy-2-nitrobenzyl benzylcarbamate. Steady-state UV–vis, fluorescence, 1H NMR, and IR spectral changes of FluAO, TruxAO, and FerroAO were consistent with already estimated C–N cleavage and the following reactions. HPLC study clarified their quantum yields of photolysis at 365 nm to be 0.012–0.034 and the formation of benzylamine from TruxAO after derivatization with 2,4-dinitrofluorobenzene. However, AtqAO showed only photoisomerization. Photocuring of trimethylolpropane triacrylate at 365 nm was initiated by FluAO, TruxAO, and FerroAO with lower efficiency than TPO and that of the thiol–ene formulation composed of diallyl phthalate and pentaerythritol tetramercaptoacetate was possible with FluAO and TruxAO. TruxAO and FerroAO were photosensitive under visible light, and the former succeeded in the photocuring of both formulations. Also, poly(glycidyl methacrylate) films containing FluAO were crosslinked upon irradiation followed by postexposure bake due to photogenerated benzylamine.