Abstract: Three cross-photodimers were synthesized by irradiation of each two monomers of 4-(2-phenylethenyl)pyridine, 2-(2-phenylethenyl)benzoxazole and 5-phenyl-2-(2-phenylethenyl) oxazole in H2SO4 solution using medium-pressure Mercury lamp (λ > 300 nm) as light source.The cross-photodimerization was monitored by HPLC titration. The results showed that three photodimers were produced in each reaction,two of them were the self-photodimers and the other one was the cross-photodimer. The cross-photodimers were isolated by column chromatography and their structures with syn-head-to-tail configurations were determined by UV, IR, 1H NMR, 13C NMR and MS. The photolysis of the cross-photodimer was performed in dilute methanol solution upon the irradiation of low-pressure Mercury lamp (λ=254 nm) and monitored by HPLC and UV titration. It was found that the cross-photodimer was photolyzed into trans-monomers at first, and then the new-formed trans-monomers were converted into cis-ones by the trans-cis isomerization.

Key words: Cross-photodimerization, Cyclobutane, Photolysis, Heteroarylethene