The photophysics of Ru(tpy)(CN)3 - and Ru(ttpy)(CN)3 - (where tpy ) 2,2¢:6¢,2¢¢-terpyridine and ttpy ) 4¢-(ptolyl)- 2,2¢:6,2¢¢-terpyridine) has been studied in detail. The complexes exhibit strongly solvatochromic behavior. Emission energies correlate linearly with solvent acceptor number, consistent with the metal-to-ligand charge transfer (MLCT) nature of the emission and the occurrence of second-sphere donor-acceptor interactions at the cyanide ligands. On the other hand, the correlation of emission lifetimes is clearly biphasic, with a sharp maximum found for solvents of intermediate acceptor number. Such a behavior is explained in terms of competition between a direct deactivation channel and an indirect, thermally activated decay pathway, with relative efficiencies depending strongly on MLCT state energy. A gain of 2 orders of magnitude in lifetime is obtained using the tricyano complexes (Ru(tpy)(CN)3 -, ô ) 48 ns in DMSO; Ru(ttpy)(CN)3 -, ô ) 40 ns in CH3CN) instead of the corresponding bis-terpyridine species (Ru(tpy)2 2+, ô ) 250 ps in CH3CN; Ru(ttpy)2 2+, ô ) 860 ps in CH3CN). This shows how an appropriate choice of ancillary ligands can be used to improve the properties of photosensitizers containing the Ru(II)-terpyridine chromophoric unit.
Design of Long-Lived Ru(II) Terpyridine MLCT States. Tricyano Terpyridine Complexes
INDELLI, Maria Teresa;BIGNOZZI, Carlo Alberto;SCANDOLA, Franco;
1998
Abstract
The photophysics of Ru(tpy)(CN)3 - and Ru(ttpy)(CN)3 - (where tpy ) 2,2¢:6¢,2¢¢-terpyridine and ttpy ) 4¢-(ptolyl)- 2,2¢:6,2¢¢-terpyridine) has been studied in detail. The complexes exhibit strongly solvatochromic behavior. Emission energies correlate linearly with solvent acceptor number, consistent with the metal-to-ligand charge transfer (MLCT) nature of the emission and the occurrence of second-sphere donor-acceptor interactions at the cyanide ligands. On the other hand, the correlation of emission lifetimes is clearly biphasic, with a sharp maximum found for solvents of intermediate acceptor number. Such a behavior is explained in terms of competition between a direct deactivation channel and an indirect, thermally activated decay pathway, with relative efficiencies depending strongly on MLCT state energy. A gain of 2 orders of magnitude in lifetime is obtained using the tricyano complexes (Ru(tpy)(CN)3 -, ô ) 48 ns in DMSO; Ru(ttpy)(CN)3 -, ô ) 40 ns in CH3CN) instead of the corresponding bis-terpyridine species (Ru(tpy)2 2+, ô ) 250 ps in CH3CN; Ru(ttpy)2 2+, ô ) 860 ps in CH3CN). This shows how an appropriate choice of ancillary ligands can be used to improve the properties of photosensitizers containing the Ru(II)-terpyridine chromophoric unit.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
