A new highly luminescent 'molecular light switch' has been prepared using osmium (II) metal and nonchromophoric phosphine (dppe) and chromophoric (dppz) ligands to study the dynamics of DNA, where dppe is cis-1,2-bis(diphenylphosphino)-ethylene and dppz is dipyrido[3,2-a:2',3'-c]phenazine. The complex, [Os(dppe)2(dppz)]2+, shows a quantum yield in acetonitrile about twofold larger than analogous ruthenium compound, [Ru(bpy)2(dppz)]2+. The anisotropy of [Os(dppe)2(dppz)]2+ was found to be near 0.2 at -60 degrees Celsius in glycerol. This compound emits at 610 nm on exciting at metal to ligand charge transfer (MLCT) band (390 nm). The lifetimes are 550 and 315 ns in argon and air equilibrated acetonitrile samples respectively. This new class of fluorophore using MLCT complex is useable for measurement of DNA dynamics over a larger time scales, which is not possible with conventional DNA dyes, such as ethidium bromide or acridine derivatives.