Electron Transfer Photoinitiating Systems. The Effect of the Co-Initiator Structure on the Photoinitiation Ability of a Photoredox Pair Containing Neutral Hemicyanine Dyes as Sensitizers

Abstract

The photoinitiation ability of photoredox pairs composed of a neutral hemicyanine dye and different co-initiators for the free radical polymerization of 2-ethyl-2-(hydroxymethyl)propane 1,3-diol triacrylate is investigated. p-(N,N-dimethylaminostyryl)benzthiazole, p-(N,N-dimethyl-aminostyryl)benzoxazole, p-(N,N-dimethylaminostyryl)α-naphthiazole are tested as dyes, and as co-initiators, an aromatic amino-acid, an aromatic thio- and oxycarboxylic acid, and alkyltriphenylborate are applied as electron donors. N,N'-dialkoxybipyridinium salts are used as ground-state electron acceptors. The experimental results show that the photoinitiating ability of the tested photoredox pairs are controlled by both the driving force of the electron transfer process between an electron donor and an electron acceptor and the reactivity of the free radical that results from the secondary reactions occurring after the photoinduced electron transfer process. The greatest photoinitiation ability of free radical polymerization is observed when the tested dyes are applied as electron enna donors in their singlet excited states in combination with N,N'-dialkoxybipyridinium salts acting as ground-state electron acceptors.