Disclosed are of the protected photoinitiators of the formula: wherein Aryl1 is an aromatic or heteroaromatic ring; Aryl2 is an aromatic ring; each R1 is an alkyl, an aryl, an electron donating group or an electron withdrawing group, and subscript a is 0 to 3; each R2 is an alkyl, an aryl, an electron donating group or an electron withdrawing group, and subscript b is 0 to 3; Prot is a protected carbonyl group.