The photochemicalreaction of some halogenoheterocycles substituted with electron withdrawing groups with acrylonitrile gave the addition product in high yields. The irradiation of 2-acetyl-5-phenylthiophene at 355 nm with a Nd:YAG laser in the presence of phenylacetylene gave 1-phenylnaphthalene, probably formed from the tripletstate of phenylacetylene. 2-Acetyl-5-phenylthiophene is a sensitizer