Premium
Photoinduced Energy‐ and Electron‐Transfer Processes in Dinuclear Ru II –Os II , Ru II –Os III , and Ru III –Os II Trisbipyridine Complexes Containing a Shape‐Persistent Macrocyclic Spacer
Author(s) -
Venturi Margherita,
Marchioni Filippo,
Ferrer Ribera Belén,
Balzani Vincenzo,
Opris Dorina M.,
Schlüter A. Dieter
Publication year - 2006
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200500323
Subject(s) - chemistry , ruthenium , crystallography , electron transfer , acetonitrile , photochemistry , phenylacetylene , stereochemistry , catalysis , biochemistry , chromatography
The PF 6 − salt of the dinuclear [(bpy) 2 Ru( 1 )Os(bpy) 2 ] 4+ complex, where 1 is a phenylacetylene macrocycle which incorporates two 2,2′‐bipyridine (bpy) chelating units in opposite sites of its shape‐persistent structure, was prepared. In acetonitrile solution, the Ru‐ and Os‐based units display their characteristic absorption spectra and electrochemical properties as in the parent homodinuclear compounds. The luminescence spectrum, however, shows that the emission band of the Ru II unit is almost completely quenched with concomitant sensitization of the emission of the Os II unit. Electronic energy transfer from the Ru II to the Os II unit takes place by two distinct processes ( k en = 2.0×10 8 and 2.2×10 7 s −1 at 298 K). Oxidation of the Os II unit of [(bpy) 2 Ru( 1 )Os (bpy) 2 ] 4+ by Ce IV or nitric acid leads quantitatively to the [(bpy) 2 Ru II ( 1 )Os III (bpy) 2 ] 5+ complex which exhibits a bpy‐to‐Os III charge‐transfer band at 720 nm ( ε max =250 M −1 cm −1 ). Light excitation of the Ru II unit of [(bpy) 2 Ru II ( 1 )Os III (bpy) 2 ] 5+ is followed by electron transfer from the Ru II to the Os III unit ( k el,f = 1.6×10 8 and 2.7×10 7 s −1 ), resulting in the transient formation of the [(bpy) 2 Ru III ( 1 )Os II (bpy) 2 ] 5+ complex. The latter species relaxes to the [(bpy) 2 Ru II ( 1 )Os III (bpy) 2 ] 5+ one by back electron transfer ( k el,b = 9.1×10 7 and 1.2×10 7 s −1 ). The biexponential decays of the [(bpy) 2 *Ru II ( 1 )Os II (bpy) 2 ] 4+ , [(bpy) 2 *Ru II ( 1 )Os III (bpy) 2 ] 5+ , and [(bpy) 2 Ru III ( 1 )Os II (bpy) 2 ] 5+ species are related to the presence of two conformers, as expected because of the steric hindrance between hydrogen atoms of the pyridine and phenyl rings. Comparison of the results obtained with those previously reported for other Ru–Os polypyridine complexes shows that the macrocyclic ligand 1 is a relatively poor conducting bridge.