Dinuclear metal-organic material for binary optical recording

A diimine ligand tethered to anthracene in the 9-position, 4'-(9-anthrylethyl)-4-methyl-2,2'-bipyridine (bpy-An), was dimerized through cycloaddition photochemistry. The resultant head-to-tail photodimer (bpy-PD) was used as a bridging ligand in the preparation of a new dinuclear Ru-II complex, [Ru(dmb)(2)(bpy-PD)Ru(dmb)(2)](4+) (dmb=4,4'-dimethyl-2,2'-bipyridine). The corresponding mononuclear species containing anthracene ([Ru(dmb)(2)(bpy-An)](2+), was also synthesized and serves as a model compound in this study. UV photolysis (lambda < 300 nm) of the strongly luminescent Ru-II dinuclear complex results in cycloreversion, generating two anthracene-containing mononuclear species, [Ru(dmb)(2)(bpy-An)](2+), whose emission is largely quenched as a result of nonradiative triplet-triplet energy transfer. The photophysical and photochemical properties of the dinuclear system have been studied in CH3CN solutions and in solid polyvinyl alcohol (PVA) thin films. The on-off luminescence switching characteristics and concomitant non-destructive readout properties suggested that these molecules could be useful in read-only memory (ROM) applications. In the solid state, micrometer-sized objects were imaged using visible light, taking advantage of the luminescence contrast generated from the UV photochemical reaction. These written images were stable for at least 6 months. indicating that long-term binary data storage is indeed feasible in these ROM metal-organic materials.