Three‐cationic carbocyanine dyes as sensitizers in very efficient photoinitiating systems for multifunctional monomer polymerization

Abstract

AbstractThis article is focused on the description of the synthesis, spectroscopic, electrochemical properties, and the free radical photoinitiation abilities of new three‐cationic carbocyanine dyes. A new synthestic strategy for preparation of symmetrical cyanine dyes has been developed based on the 2‐methylbenzothiazole, 2‐methylbenzoxazole and 2,3,3‐trimethylindolinium quaternization by α‐bromo‐ω‐tertiary ammonium salts followed by the condensation of obtained product with triethyl ortho‐formate. Resulted dyes possess in one molecule three quaternary nitrogen atoms, for example, they are three‐cationic in character. Novel three‐cationic symmetric carbocyanine dyes paired with n‐butyltriphenylborate anions are very efficient photoinitiators of free radical polymerization of acrylate monomers, for example, (TMPTA) when irradiated with the visible emission of an argon‐ion laser. The photoinitiating abilities of the novel photoredox pairs were compared to the photoinitiation properties of their monocationic equivalents, for example, N,N′‐diethylthia‐, N,N′‐diethyloxa‐ and N,N′‐dimethylindocarbocyanine n‐butyltriphenylborates (SB2, OB2, and IB2) and also compared to the initiation ability of Rose Bengal derivative, for example, typical triplet state photoinitiator. The kinetic studies clearly demonstrated that the three‐cationic carbocyanine borate photoredox pairs exhibit a significant increase in the efficiency of TMPTA free radical polymerization in comparison to the photoredox pairs containing structurally related, mono‐cationic carbocyanine borates. It was also shown that, the addition of a second coinitiator to the cyanine borate salts enhances their photoinitiating abilities. The best results were obtained for three cationic carbocyanine borates in the presence of second coinitiator being N‐methoxypyridinium n‐butyltriphenylborate. The photoinitiating abilities of the systems of these types are more effective than those composed of carbocyanine cation/borate anion exclusively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4636–4654, 2009