Nonradiative Transition of Phosphorescent Charge-Transfer States of Ruthenium(II)-to-2,2‘-Biquinoline and Ruthenium(II)-to-2,2‘:6‘,2‘‘-Terpyridine in the Solid State

Abstract

Temperature-dependent decays of the charge-transfer triplet excited states (3CT) of ruthenium(II) compounds have been investigated in a wide temperature range (77−480 K) for the crystals of Ru(biq)3(ClO4)2, Ru(bpy)2(biq)X2·2H2O, and Ru(tpy)2X2, (bpy = 2,2‘-bipyridine, tpy = 2,2‘:6‘,2‘‘-terpyridine, biq = 2,2‘-biquinoline, X = ClO4 -, PF6 -). The width of the 1CT absorption band and the peak of 3CT emission of the Ru(bpy)2(biq)X2·2H2O crystal at 298 K are unchanged from those of the ethanol/methanol solution sample. The 3CT of Ru(bpy)2(biq)X2·2H2O and Ru(biq)3(ClO4)2 in the solid state above 370 K are converted to a higher lying excited state, the d−d triplet lowest excited state (3(d−d)), with a frequency factor of >1013 s-1 and an activation energy of >3100 cm-1, followed by the rapid degradation of the higher excited state. A small frequency factor (<1012 s-1) and an activation energy (<2000 cm-1) of the nonradiative decay of 3CT for [Ru(tpy)2]X2 in the solid state indicates that the exoergonic intersystem crossing of 3(d−d) to the ground state is the rate-determining process of 3CT decay above 200 K.

Synthesis and Application of New Ruthenium Complexes Containingβ-Diketonato Ligands as Sensitizers for Nanocrystalline TiO2Solar Cells

“…All complexes 1-5 show an emission at 298 K with a maximum between 990 nm and 1010 nm. The blue shift that occurs for all of the complexes in the transition from fluid solution to frozen solvent glass is a common rigidochromic effect observed in many metal diamine complexes [21,22]. The emission spectra of complex 1 in ethanol-methanol mixed solvents at 77 and 298 K are presented in complex 1 exhibits an emission maximum at 990 nm, which is 50 nm red-shifted compared to that of the R1 emission and consistent with the shift in the lowest-MLCT absorption band.…”

“…The enhanced red absorption of these complexes renders them attractive candidates as panchromatic charge transfer sensitizers for DSCs. It is well known that the excited-state responsible for the luminescence of the Ru(II)-polypyridine compounds is the lowest-energy triplet metal-to-ligand charge-transfer ( 3 MLCT) state [21]. When excited at the charge transfer absorption band, complexes 1-5 show an intense emission at the 77 K ethanol-methanol glass matrix with a maximum between 930 and 970 nm.…”

Low Quantum Yields of Relaxed Electron Transfer Products of Moderately Coupled Ruthenium(II)−Cobalt(III) Compounds on the Subpicosecond Laser Excitation

“…After a transition to the Gibbs free energy surface of reactant, the nitrogen atoms of pyridyl groups get closer to the cobalt during its oxidation from 213 pm 32 to 193 pm 33 2+ , which was estimated to be 2.1 and 2.8 eV, respectively, from the temperature dependence of radiation-less transition rate of 3 -CT(Ru). 35,36 The peak energy of the triplet excited d-d transition of [Co(tpy) 2 ] 3+ is shifted from the 0-0 energy by the FranckCondon energy of optical transition, which is estimated to be 0.75 eV from the Stokes shift (1.5 eV ) 3.2 eV (the absorption peak) -1.7 eV (the phosphorescence)) in the case of [Co(CN) 6 ] 3-. 37 Since the weaker ligand-field of [Co(tpy) 2 ] 3+ than [Co(CN) 6 ] 3-is assumed to reduce the Franck-Condon energy of the optical singlet-triplet d-d transition to 0.4 eV, the enthalpy of the formation of lowest triplet state is close to 1 eV.…”

Ultrafast excited states dynamics of [Ru(bpy)3]2+ dissolved in ionic liquids

“…For [Ru(bpy) 3 ] 2+ , the 3 MC state was found to be energetically higher than the 3 MLCT state. 40,42,43 Therefore, the quenching of the 3 MLCT luminescence via the 3 MC state appears to be thermally activated. 44,45 However, the population of this intermediate state remains negligible at all times due to the much higher relaxation rate of 3 MC to 1 A 1 .…”