Photosensitized generation of singlet oxygen from ruthenium(ii) and osmium(ii) bipyridyl complexes

Abstract

Photophysical properties for a number ruthenium(II) and osmium(II) bipyridyl complexes are reported in dilute acetonitrile solution. The lifetimes of the excited metal to ligand charge transfer states (MLCT) of the osmium complexes are shorter than for the ruthenium complexes. Rate constants, kq, for quenching of the lowest excited metal to ligand charge transfer states by molecular oxygen are found to be in the range (1.1-7.7) x 10(9) dm3 mol(-1) s(-1). Efficiencies of singlet oxygen production, fDeltaT, following oxygen quenching of the lowest excited states of these ruthenium and osmium complexes are in the range of 0.10-0.72, lower values being associated with those compounds having lower oxidation potentials. The rate constants for quenching of the excited MLCT states, kq, are found to be generally higher for osmium complexes than for ruthenium complexes. Overall quenching rate constants, kq were found to give an inverse correlation with the energy of the excited state being quenched, and also to correlate with the oxidation potentials of the complexes. However, when the contribution of quenching due exclusively to energy transfer to produce singlet oxygen, kq1, is considered, its dependence on the energy of the excited states is more complex. Rate constants for quenching due to energy dissipation of the excited MLCT states without energy transfer, kq3, were found to show a clear correlation with the oxidation potential of the complexes. Factors affecting both the mechanism of oxygen quenching of the excited states and the efficiency of singlet oxygen generation following this quenching are discussed. These factors include the oxidation potential, the energy of the lowest excited state of the complexes and spin-orbit coupling constant of the central metal.

Excited state behaviour of substituted dipyridophenazine Cr(iii) complexes in the presence of nucleic acids

“…They more than double when the solution is nitrogen flushed, consistent with energy transfer quenching of the excited state by dissolved molecular oxygen (3O 2 ), as shown previously for other Cr(III) complexes. [37][38] Rate constants for quenching by oxygen (kq) 39 calculated using an oxygen concentration of 288 mM (20 C) are collected in Table 1. 40 The lifetimes in both aerated and degassed solution are slightly longer for the triflate salt, possibly indicative of weak quenching by chloride as has been suggested by Neshvad et al 41 The emission lifetime of each complex in aerated solution was found to decrease when its concentration was increased.…”

Long-wavelength fluorescence lifetime labels

“…7). In this context, it is probably also worth mentioning that certain Os metal-ligand complexes are toxic [143,144], but according to recent investigations, the toxicity and phototoxicity of Os complexes are comparable with Ru and Rh MLCs [145][146][147].…”

Variation of DNA photocleavage efficiency for [(TL)2Ru(dpp)]Cl2 complexes where TL=2,2′-bipyridine, 1,10-phenanthroline, or 4,7-diphenyl-1,10-phenanthroline

“…The complex [(bpy) 2 Ru(dpp)] 2+ (where dpp = 2,3-bis(2-pyridyl)pyrazine) has been shown to photochemically generate singlet oxygen ( 1 O 2 ) [14]. Excitation of [(bpy) 2 Ru(dpp)] 2+ at 465 nm produces the 3 MLCT state with unit efficiency.…”

“…Excitation of [(bpy) 2 Ru(dpp)] 2+ at 465 nm produces the 3 MLCT state with unit efficiency. The 3 MLCT state is quenched by oxygen to produce 1 O 2 with U = 0.31 ± 0.2 (in air equilibrated acetonitrile) [14]. The ability of [(bpy) 2 Ru(dpp)] 2+ to produce singlet oxygen has been examined though the characteristic emission of 1 O 2 at 1270 nm [14].…”