CHROMOPHORE-QUENCHER PROBES FOR DNA

A series of compounds which contain the (bpy)Re-1 (CO)(3)-chromophore (abbreviation = Re) covalently linked to an anthracene chromophore (ab breviation = An) by flexible tethers of various lengths have been subj ected to photophysical study in homogenous solution and in solution wi th calf thymus DNA. In homogeneous solution the fluorescence of the An chromophore and the metal-to-ligand charge transfer (MLCT) luminescen ce from the Re chromophore are strongly quenched, An fluorescence quen ching is attributed to A-->Re E(n) T via the Forster dipole-dipole cou pling mechanism, while MLCT quenching is assigned to Re-->An E(n) T vi a the Dexter spin-exchange mechanism. In homogenous solution the effic iency of both E(n) T pathways is high and there is only a weak depende nce of E(n) T rates on the length of the flexible spacer. Photophysica l studies of the same compounds in the presence of DNA reveal that the complexes exhibit a strong proclivity for binding to DNA via intercal ation of the An chromophore. Furthermore, DNA binding is accompanied b y a substantial increase in the yield of the MLCT emission. The increa se in MLCT emission yield is attributed to a decrease in the rate of R e-->An E(n) T which is caused by a change in the conformation of the f lexible tether.