Visible photosensitizers for photopolymerizable compositions

In a photopolymerizable composition comprising at least one ethylenically unsaturated monomer capable of free radical initiated addition polymerization and an initiator system activatable by actinic radiation comprising a sensitizer, wherein said photoinitiator system is present in an amount sufficient to initiate polymerization of said monomer on exposure of said composition to actinic radiation, the improvement comprising said sensitizer is a compound of structure:

• ##STR20## wherein:
• R.sub.1 is (1) hydrogen, (2) substituted or unsubstituted alkyl of 1 to 8 carbon atoms, (3) CH.sub.2 .dbd.CHCO--, (4) CH.sub.2 .dbd.C(CH.sub.3)CO-- (5) R.sub.15 CO--, where R.sub.15 is a substituted or unsubstituted aryl of 5 to 10 atoms or a substituted or unsubstituted alkyl containing 1 to 8 carbon atoms;
• and
• R.sub.2 and R.sub.3, alike or different, are selected from the group consisting of:
• ##STR21## wherein:
• n is 0 or 1;
• R.sub.4 and R.sub.5 are each independently hydrogen, chloro, hydroxyl, alkyl of 1 to 6 carbon atoms, and alkoxyl of 1 to 6 carbon atoms;
• and ##STR22## wherein:
• X is O, S, Se, NR.sub.12, or CR.sub.13 R.sub.14 where R.sub.12, R.sub.13, and R.sub.14 are each independently alkyl of 1 to 6 carbon atoms or substituted or unsubstituted phenyl;
• R.sub.6 is hydrogen or substituted or unsubstituted alkyl or 1 to 4 carbon atoms;
• R.sub.7 is (1) substituted or unsubstituted alkyl of 1 to 8 carbon atoms or (2) substituted or unsubstituted aryl of 5 to 10 atoms;
• R.sub.8, R.sub.9, R.sub.10, and R.sub.11 each independently hydrogen, halogen, dialkylamino, substituted or unsubstituted alkyl of 1 to 6 carbon atoms, substituted or unsubstituted alkoxyl of 1 to 6 carbon atoms, substituted or unsubstituted thioalkoxyl of 1 to 6 carbon atoms, or substituted phenyl;
• or
• (R.sub.8 and R.sub.9), (R.sub.9 and R.sub.10), or (R.sub.10 and R.sub.11) are joined in a substituted or unsubstituted aromatic ring of 5 to 10 atoms.