Novel DNA-photocleaving molecule 1 consisting of a p-cyano substituted benzophenone photophore and an alkyl amino side chain was developed. DNA cleavage by 1 under photoirradiation conditions occurred selectively at 5′ side G of 5′ GG3′ sequence after hot piperidine treatment. Photoirradiation of deoxyguanosine at 312 nm in the presence of 1 efficiently produced imidazolone as a predominant product.