Enhanced activity as polymerization photoinitiators of Rose Bengal and Eosin esters with an O-benzoyl-alpha-oxooxime group: The role of the excited state reactivity
D. Burget et al., Enhanced activity as polymerization photoinitiators of Rose Bengal and Eosin esters with an O-benzoyl-alpha-oxooxime group: The role of the excited state reactivity, ACT POLYM, 50(9), 1999, pp. 337-346
New Eosin and Rose Bengal ester with an O-benzoyl-alpha-oxooxime group were
synthesized and evaluated as visible light photoinitiators for polymerizat
ion in the presence of an amine. The dyes EO-AO and RB-AO are clearly bette
r photoinitiators, with higher Rp values, than the corresponding physical m
ixtures dye/acyloxime, or than the corresponding pure dyes. However, the re
lative efficiencies of the different dye/amine and dye/amine/AO mixtures sh
ow that if RB is better than EO in the binary mixture, the situation was re
versed after addition of AO. The spectroscopic and electrochemical properti
es of the dyes were measured and the forecasts of thermodynamic calculation
s were confirmed by time resolved laser spectroscopy experiments which show
that the species formed by reaction of the excited dyes eosin and RB with
AO were not the same. One observes the dominating formation of the oxidized
form of the acyloxime with eosin and its reduced form in the case of Rose
Bengal which lead in the case of EO to a larger amount of radicals per phot
on absorbed and a better initiating efficiency.