An argon laser induced polymerization photoinitiated by both mono- and bichromophoric hemicyanine dye–borate salt ion pairs. The synthesis, spectroscopic, electrochemical and kinetic studies

A series of homodimeric hemicyanine dyes based on (p-dimethylaminostyryl)benzothiazolium, (p-dimethylaminostyryl)benzoxazolium, (p-dimethylaminostyryl)-2,3,3-trimethyl-3H-indolium residues were synthesized. Several photoredox pairs containing mono- and bichromophoric hemicyanine dyes, possessing benzothiazole, benzoxazole or indolinium group linked by 5 or 10 methylene groups have been evaluated as novel photoinitiators for free radical polymerization induced with the argon-ion laser visible emission. In tested photoredox pairs, hemicyanine dye acts as an electron acceptor and it is coupled with borate anion which is an electron donor. The photochemistry of the series of bichromophoric hemicyanine borates: 1,5-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)benzothiazolium]pentane, 1,10-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)benzothiazolium]decane (S5, S10), 1,5-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)benzoxazolium]pentane, 1,10-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)benzoxazolium]decane (O5, O10) and 1,5-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)-3,3,3′,3′-tetramethyl-3H-indolium]pentane, 1,10-bis-[N,N′-(2,2′-(4-N,N-dimethylamino)styryl)-3,3,3′,3′-tetramethyl-3H-indolium]decane (I5, I10) was compared to the photochemistry of structurally related monochromophoric hemicyanine borates (S1, O1, I1).