Photosensitized Generation of Singlet Oxygen from Vinyl Linked Benzo-Crown-Ether−Bipyridyl Ruthenium(II) Complexes

Abstract

Photophysical properties of 10 substituted methoxybenzene or vinyl linked benzo-crown-ether−2,2‘-bipyridyl ruthenium(II) complexes are reported. The lifetimes of the excited triplet metal to ligand charge transfer states, 3MLCT, of the complex ions are in the range 0.85 ± 0.12 μs with two exceptions where the lifetime drops to about half this value. The rate constants, k q, for quenching in acetonitrile of the 3MLCT states of these ruthenium complex ions by molecular oxygen, O2(3Σg -), and the variations in the efficiency, , with which excited singlet oxygen, O2*(1Δg), is thereby produced are reported. The quenching rate constants are in the range 2.2−4.2 × 109 dm3 mol-1 s-1, and efficiencies of singlet oxygen production are in the range 0.21−0.74. Those complexes with the highest values of k q tend to be those with lowest values; that is, k q and show a reasonable inverse correlation. The product k q gives the rate constant for oxygen quenching with energy transfer to oxygen, , and k q − gives the rate constant, , for oxygen quenching by any path which does not lead to energy transfer. The values of , , and k q are compared with those in the literature which are mainly available for organic sensitizers of singlet oxygen. The similarities and differences between these two classes of compounds are discussed taking into account the fact that ruthenium complex ions are likely to show enhanced intersystem crossing, due to the heavy atom effect and the likely dependence of and , and thereby the efficiencies of singlet oxygen production, on the energies of the excited 3MLCT states and on steric factors.

Photosensitized singlet oxygen and its applications

“…In water, however, F D was found to be about half of P T O 2 ; thus energy transfer must not found be the only quenching pathway available to the excited RuL 3 complexes. Tanielian et al [38] Substituted ethoxybenzene or vinyl-linked benzocrown-ether-2,2?-bipyridine Ru(II) complexes have been tested for singlet oxygen producing ability, with efficiencies in the range of 0.18 Á/0.47 [39]. A related series of aza-15-crown-5-vinyl-2,2?-bipyridine Ru(II) complexes and multinuclear Ru(II) complexes were investigated by Abdel-Shafi et al [40].…”

“…Complexes containing at least one benzoaza-15-crown-5-bipyridine substituent had much lower oxidation potentials and lower f values, in the range of 0.26 Á/0.31. The authors suggest that those ligands with extended conjugation and with low oxidation potentials could be physically quenching the singlet oxygen in the precursor molecule, before dissociation occurs [39].…”

A New Heteroleptic Ruthenium(II) Polypyridyl Complex with Long‐Wavelength Absorption and High Singlet‐Oxygen Quantum Yield

“…2 + as the standard (F = 0.57 in CH 3 CN) [13] and 1,3-diphenylisobenzofuran (DPBF) as the trapping agent of 1 O 2 . The 1 O 2 quantum yields were measured to be 0.79…”

“…1 O 2 quantum yields of the complexes were determined by using [Ru-A C H T U N G T R E N N U N G (bpy) 3 ] 2 + as the reference (F = 0.57 in CH 3 CN) [13] and DPBF as the trapping agent of 1 O 2 . [24] …”

Unexpected high photothemal conversion efficiency of gold nanospheres upon grafting with two-photon luminescent ruthenium(II) complexes: A way towards cancer therapy?

“…Singlet oxygen sensor (DPBF), that is highly selective for singlet oxygen, was used to (Φ s Δ = 0.81) [39].…”