Ns. Allen et al., PHOTOCHEMISTRY AND PHOTOINITIATOR PROPERTIES OF 2-SUBSTITUTED ANTHRAQUINONES .2. PHOTOPOLYMERIZATION AND FLASH-PHOTOLYSIS, Polymer, 36(24), 1995, pp. 4665-4674
The photoinduced polymerization activities of fifteen 2-substituted an
thraquinones have been determined in different monomers and prepolymer
s using real-time Fourier-transform infra-red spectroscopy and photoca
lorimetry. The relative order in photoinitiator efficiency is found to
be highly dependent upon the method used, the nature of the light sou
rce, amine co-synergist and monomer being crucial factors. Oxygen quen
ching in all cases indicates that the triplet state is the active prec
ursor. Without an amine co-synergist, absolute quantum-yield measureme
nts show that anthraquinones with electron-withdrawing groups are more
active than those which are electron-donating. However, in the presen
ce of a tertiary amine and under polychromatic illumination, the effec
ts are different. In the latter case amido derivatives with long-wavel
ength charge-transfer bands and mixed n pipi pi* triplet states tend
to be more reactive. Fluorescence and phosphorescence analyses indicat
e a high rate of intersystem crossing to the triplet state. The relati
ve positions of the lowest excited singlet pi pi and second excited n
pi triplet states play an important role in determining their photoa
ctivities, as shown in paper 1. Seraiquinone radical and radical-anion
intermediates are observed using microsecond flash phorolysis and the
data interrelated to their spectroscopic and photopolymerization acti
vities. The haloanthraquinones are shown to undergo an additional mech
anism involving dehalogenation.