In a continuation of our research on new chromophores for photoinitiators (PIs), we investigated a triple-bond-containing benzophenone derivative. 1,5-Diphenyl-1,4-pentadiyn-3-one (2) was prepared from phenylacetylene and ethyl formate by a one-pot reaction. Differential scanning photocalorimetry experiments in lauryl acrylate of 2 showed surprisingly high activity for the double-bond conversion and rate of polymerization at the lowest PI concentrations and even without any coinitiator. By the application of monomers with abstractable hydrogens, significant improvement in the photoreactivity was observed. Ultraviolet-visible spectroscopy revealed strong absorption up to 350 nm. Steady-state photolysis experiments proved that the photochemistry of this compound was faster than that of benzophenone. (C) 2004 Wiley Periodicals, Inc.