In order to create molecules for photochemotherapy (PCT) it is vital to create photoactive molecules that absorb low energy light and have tunable excited state properties. The monometallic complex [Ru(biq)2(dpb)][PF6]2 (biq = 2.2'-biquinoline; dpb = 2,3-bis(2-pyridyl)benzoquinoxaline) is a potential new PCT agent that undergoes ligand dissociation of the dpb ligand when irradiated with visible light. The dpb ligand is a known anticancer agent through the production of singlet oxygen. The substitution of the dpb ligand is attributed to the steric strain of the molecule imposed by the bulkiness of the biq ligands. This steric strain is demonstrated in the lengthening of the Ru-dpb bonds and twisting of the biq and dpb ligands in the resulting crystal structure. The coordination of rhenium carbonyl chloride to the dpb bridging ligand to yields [(biq)2Ru(dpb)Re(CO)3Cl][PF6]2. The absorption associated with the Ru-dpb 3MLCT of the bimetallic complex red-shifts into the the optimum PCT window. However, the coordination of the second metal stabalizes the complex and, as a result, no photosubstitution is observed. Despite the considerable torsional strain of the biq ligands in the crystal structure of the bimetallic, the Ru-dpb bond lengths decrease, and the dpb ligand becomes more planar, indicating the stabilizing effect of the rhenium carbonyl moiety. The results indicate that both electronic and structural considerations are critical in the design of PCT agents that undergo photosubstitution of bidentate ligands. Furthermore, we have shown the possibility of stabilizing photolabile Ru(II) complexes by coordinating another metal, which has applications in bimetallic catalysis.

Photoinduced properties of bimetallic polypyridyl complexes

249th National Meeting (2015)

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