134438-71-4Relevant articles and documents
Photophysical Properties of Polypyridyl Carbonyl Complexes of Rhenium(I)
Worl, Laura A.,Duesing, Rich,Chen, Pingyun,Ciana, Leopoldo Della,Meyer, Thomas J.
, p. 849 - 858 (1991)
The photophysical properties of the metal to ligand charge transfer (m.l.c.t.) excited states of the complexes (X=NH2, NEt2, NHCOCH3, OCH3, CH3, H, Ph, Cl, CO2Et or NO2; bipy = bipyridine) vary systematically as the substituent X is varied.For the cases where m.l.c.t. states are lowest lying a quantitative correlation exists between ln(knr x 1 s) (knr is the rate constant for nonradiative decay) and the Franck-Condon factor calculated from parameters obtained by emission spectral fitting.The solvent reorganizational energy for has been determined to be 1100 cm-1 in EtOH-MeOH -(4:1 v/v) and 650 cm-1 in 2-methyltetrahydrofuran by a temperature dependent bandwidth study.Based on a comparative analysis of properties with related polybipyridyl complexes of RuII and OsII it has been concluded that: (1) the extent of distortion at the 4,4'-X2-bipy acceptor ligand correlates with the energy gap between the excited and ground states; these results are in agreement with an earlier correlation found for polypyridyl complexes of OsII; (2) the unusually large Stokes shift and the broadening of the vibronic components in absorption and emission spectra arise from a combination of increased solvent reorganizational energies and greater distortions in the low-frequency modes between the excited and ground states; and (3) the relatively short lifetimes for the complexes of ReI have as a major contributing factor the participation of a ν(CO) mode at ca. 2020-2040 cm-1 as an energy acceptor in non-radiative decay.
Substituent constant correlations as predictors of spectroscopic, electrochemical, and photophysical properties in ring-substituted 2,2′-bipyridine complexes of rhenium(I)
Hino, Janel K.,Della Ciana, Leopoldo,Dressick, Walter J.,Sullivan, B. Patrick
, p. 1072 - 1080 (2008/10/08)
The synthesis and the spectroscopic, electrochemical and photo-physical properties of the homologous series of photosensitizers, fac-[4,4′-X2-5,5′-Y 2-2,2′-bipyridine]Re(CO)3Etpy+ (X = NEt2, Me, OMe, H, Ph, Cl, CO2Me, NO2, Y = H; X = Y = Me; Etpy = 4-ethylpyridine) are described. Both the quasi-reversible or irreversible oxidation of the Re(I) center and the reversible or quasi-reversible, one-electron reduction of the coordinated bipyridyl ligand are observed to vary with the electron donor/acceptor abilities of X, Y as measured by the sum of the Hammett substituent constants σm + σp. Hammett (σT = σp + σm) values for the X, Y groups are observed to correlate linearly with the metal-to-ligand charge-transfer (MLCT) absorption and emission energies and provide a convenient tool for the estimation of excited-state properties of the complexes. The complexes are moderately strong excited-state oxidants (E1/2(+*/0) = 0.73-1.12 V vs SSCE) and exhibit emission maxima in the range 528 nm (X = NEt2, Y = H) to 755 nm (X = NO2, Y = H). MLCT excited-state decay is dominated by nonradiative decay from the 3MLCT state to the ground state and is governed by an energy gap law . It is shown that excited-state properties such as absorption energy, emission energy, rate of nonradiative decay (knr), and the rate of radiative decay (kr) correlate with σT. The correlations can be derived from more fundamental considerations. The dependence of In knr on emission energy is similar to values obtained in earlier studies with bipyridyl Ru(II) or Os(II) complexes which do not contain coordinated CO and somewhat less than that observed in a previous study for fac-(bpy)Re(CO)3(L′)+ complexes (L′ = monodentate, neutral ligands). This behavior is interpreted as an indication that nonradiative decay involves acceptor modes that are predominantly ring-based vibrations of the substituted bipyridine ligand, but that CO modes are also involved.
