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 itsdinuclear Ru(II) and Os(II) complexes, [(bpy)2Ru(m-L)Ru(bpy)2](PF6)4 (Ru2; bpy = 2,2-bipyridine) and[(Me2-bpy)2Os(m-L)Os(Me2-bpy)2](PF6)4 (Os2; Me2-bpy = (4,4'-dimethyl)-2,2'-bipyridine), are reported.The absorption spectra of the compounds are dominated by the structured bands of the PBI subunitdue to the lowest-energy spin-allowed p–p* transition. The spin-allowed MLCT transitions in Ruand Os are inferred by the absorption at 350–470 nm, where the PBI absorption is negligible. The absorptionband extends towards the red region for Os2 due to the spin-forbidden MLCT transitions, intensifiedby the heavy osmium center. The reduction processes of the compounds are dominated by two successivemono-electronic PBI-based processes, which in the metal complexes are slightly shifted compared to the freeligand. On oxidation, both metal complexes undergo an apparent bi-electronic process (at 1.31 V vs. SCE for Ruand 0.77 V for Os2), attributed to the simultaneous one-electron oxidation of the two weakly-interacting metalcenters. In Ru2 and Os2, the intensefluorescence of L subunit (lambda max 535nm;tau,4.3ns; phi, 0.91) is fullyquenched, mainly by photoinduced electron transfer from the metal centers, on the ps timescale (time constant,11 ps in Ru2 and 3 ps in Os2). Such photoinduced electron transfer leads to the formation of a charge-separatedstate, which directly decays to the ground state in about 70 ps in Os, but produces the triplet p–p* state of thePBI subunit in 35 ps in Ru2. The results provide information on the excited-state processes of the hybrid speciescombining two dominant classes of chromophore/luminophore species, the PBI and the metal polypyridinecomplexes, and can be used for future design on new hybrid species with made-to-order properties.