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Photophysical Properties and Photochemical Behaviour of Ruthenium(II) complexes containing the 2,2′‐bipyridine and 4,4′‐diphenyl‐2,2′‐bipyridine ligands
Author(s) -
De Cola Luisa,
Barigelletti Franceso,
Cook Michael J.
Publication year - 1988
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19880710407
Subject(s) - chemistry , ruthenium , excited state , photochemistry , bipyridine , 2,2' bipyridine , population , metal , electrochemistry , crystallography , electrode , organic chemistry , crystal structure , physics , demography , sociology , nuclear physics , catalysis
The temperature dependence of the emission lifetime of the series of complexes Ru(bpy) n (4,4′‐dpb) 2+ 3−(bpy = 2,2′bipyridine, 4,4′‐dpb = 4,4′‐diphenyl‐2,2′‐bipyridine) has been studied in propionitrile/butyronitrile (4:5 v/v ) solutions in the range 90–293 K. The obtained photophysical parameters show that the energy separation between the metal‐to‐ligand charge tranfer ( 3 MLCT) emitting level and the photoreactive metal‐centered ( 3 MC) level changes across the series ( ΔE = 3960, 4100, 4300, and 4700 cm −1 for Ru(bpy) 2+ 3 ), Ru(bpy)2(4,4′‐dpb) 2+ , Ru(bpy)(4,4′‐dpb) 2+ 2 , and Ru(4,4′‐dpb) 2+ 3 , respectively, where ΔE is the energy separation between the minimum of the 3 MLCT potential curve and 3 MLCT – 3 MC crossing point. Comparison between spectral and electrochemical data indicated that the changes in ΔE are due to stabilization of the MLCT levels in complexes containing 4,4′‐dpb with respect to Ru(bpy) 2+ 3 . The photochemical data for the same complexes (as I − salts) have been obtained in CH 2 Cl 2 in the presence of 0.01 M Cl − upon irradiation at 462 nm. The complexes containing 4,4′‐dpb are more photostable than Ru(bpy) 2+ 3 . Comparison between the data for thermal population of the 3 MC photoreactive state and those for photochemistry indicated that the overall photochemical process is governed by ( i ) a thermal redistribution between the emitting and photoreactive excited states, and ( ii ) mechanistic factors, likely related to the size of the detaching ligand.