Multichromophoric hybrid species made of perylene bisimide derivatives and Ru(ii) and Os(ii) polypyridine subunits

Herein, the synthesis and the photophysical and redox properties of a new perylene bisimide (PBI) species (L), bearing two 1,10-phenanthroline (phen) ligands at the two imide positions of the PBI, and its dinuclear Ru(II) and Os(II) complexes, [(bpy)(2)Ru(m-L)Ru(bpy)(2)](()PF6)(4) (Ru-2; bpy = 2,2'-bipyridine) and [(Me-2-bpy)(2)Os(mu-L) Os(Me-2-bpy)(2)](PF6)(4) (Os-2; Me-2-bpy = (4,4'-dimethyl)-2,2'-bipyridine), are reported. The absorption spectra of the compounds are dominated by the structured bands of the PBI subunit due to the lowest-energy spin-allowed pi-pi* transition. The spin-allowed MLCT transitions in Ru-2 and Os-2 are inferred by the absorption at 350-470 nm, where the PBI absorption is negligible. The absorption band extends towards the red region for Os-2 due to the spin-forbidden MLCT transitions, intensified by the heavy osmium center. The reduction processes of the compounds are dominated by two successive mono-electronic PBI-based processes, which in the metal complexes are slightly shifted compared to the free ligand. On oxidation, both metal complexes undergo an apparent bi-electronic process (at 1.31 V vs. SCE for Ru-2 and 0.77 V for Os-2), attributed to the simultaneous one-electron oxidation of the two weakly-interacting metal centers. In Ru-2 and Os-2, the intense fluorescence of L subunit (lambda(max), 535 nm; tau, 4.3 ns; Phi, 0.91) is fully quenched, mainly by photoinduced electron transfer from the metal centers, on the ps timescale (time constant, 11 ps in Ru-2 and 3 ps in Os-2). Such photoinduced electron transfer leads to the formation of a charge-separated state, which directly decays to the ground state in about 70 ps in Os-2, but produces the triplet pi-pi* state of the PBI subunit in 35 ps in Ru-2. The results provide information on the excited-state processes of the hybrid species combining two dominant classes of chromophore/luminophore species, the PBI and the metal polypyridine complexes, and can be used for future design on new hybrid species with made-to-order properties.