Photobleachable initiator systems

A compound suitable for use as a photobleachable sensitizer having the following structure:

• ##STR35## wherein R.sub.1 is (1) hydrogen, (2) substituted or unsubstituted alkyl of 1 to 8 carbon atoms, or (3) R.sub.15 CO--, where R.sub.15 is a substituted or unsubstituted aryl or heteroaryl of 5 to 10 atoms or a substituted or unsubstituted alkyl of 1 to 8 carbon atoms;
• and
• R.sub.2 and R.sub.3, alike or different, are selected from the group consisting of:
• ##STR36## wherein n is 0 or 1;
• R.sub.4 and R.sub.5 are each independently hydrogen, hydroxyl, halogen, alkyl of 1 to 6 carbon atoms, and alkoxyl of 1 to 6 carbon atoms;
• and ##STR37## wherein:
• X is 0, S, Se, NR.sub.12, or CR.sub.13 R.sub.14, where R.sub.12, R.sub.13, and R14 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 of 1 to 4 carbon atoms;
• R.sub.7 is (1) substituted or unsubstituted alkyl or cycloalkyl of 1 to 8 carbon atoms or (2) substituted or unsubstituted aryl or heteroaryl of 5 to 10 atoms;
• or
• R.sub.6 and R.sub.7 are joined together to form a 5- to 7-membered substituted or unsubstituted heterocyclic ring;
• R.sub.8, R.sub.9, R.sub.10, and R.sub.11 each independently hydrogen, halogen, dialkylamino, substituted or unsubstituted alkyl or cycloalkyl of 1 to 6 carbon atoms, or substituted or unsubstituted alkoxyl of 1 to 6 carbon atoms;
• 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.