Intrigued by the good performance of 1,5-diphenylpenta-1,4-diyn-3-one (DPD) as photoinitiator for radical polymerization we prepared and investigated several donor substituted derivatives. UV-Vis spectroscopy revealed a gradual red-shift of) ma and higher extinction in the order of the donor capability. A methoxy-substituted derivative (O-DPD) exhibited significant photoinitiation activity in photo-DSC experiments. Steady state photolysis experiments showed decreased decomposition rates with increasing donor capability. A dimethylamino derivative N-DPD was even photostable under these conditions. Because of to the D-pi-A-pi-D system of these compounds two-photon induced 31) photopolymerization experiments were performed and N-DPD showed outstanding performance compared to often applied single photon initiators. (C) 2007 Wiley Periodicals, Inc.