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Keywords:

  • Chromophores, metal-organic;
  • Data storage, optical;
  • Energy transfer;
  • Photoluminescence;
  • Photonics

Abstract

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 RuII 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 (λ < 300 nm) of the strongly luminescent RuII 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.