Singlet Oxygen Production in Water:  Aggregation and Charge-Transfer Effects

Abstract

Precise quantum yields for generation of singlet molecular oxygen, O2(1Δg), have been measured for tetrakis(4-sulfonatophenyl)porphyrin (TSPP), closely-related water-soluble porphyrin derivatives, and tris(2,2‘-bipyridyl)ruthenium(II) (bpy3Ru2+) in O2-saturated water. Under the experimental conditions, TSPP is present in an aggregated state, but the measured quantum yield for formation of O2(1Δg), ΦΔ = 0.51, remains on the same order as that of the corresponding monomer in methanol, ΦΔ = 0.70. Comparison with the quantum yield for formation of the triplet state indicates that quenching of the triplet by O2 gives O2(1Δg) with an efficiency of ca. 80%. There is a small but significant increase in ΦΔ when D2O is used in place of H2O. For the other porphyrin derivatives, the ability of the aggregate to sensitize formation of O2(1Δg) appears to depend on the total electronic charge resident on the molecule, decreasing with decreasing negative charge. A strong solvent dependence noted for O2(1Δg) production with (bpy3Ru2+) is explained in terms of competition between triplet energy transfer and photoinduced electron (or partial charge) transfer. Similar behavior could be responsible for the relatively low ΦΔ value observed for TSPP.

A study of acridine and acridinium-substituted bis(terpyridine)zinc(ii) and ruthenium(ii) complexes as photosensitizers for O2 (1Δg) generation

“…There is a clear trend of lower Φ Δ values at lower concentrations and light intensities as examined from the first few data points depicted by Tanielian et al 94 It is not within the scope of this work to evaluate such effects, but our (low concentration) data set reflects a value of 0.57 for Φ Ru(bpy)3 Δ quite well. Table 4 for explicit data) are indicated as follows: (-) < (---) < (⋯).…”

“…As 94 In the latter case, an incident light × Φ Δ vs. concentration study was also performed for [sens] > 8 × 10 −5 M. However, our sensitizer concentrations are below this threshold. There is a clear trend of lower Φ Δ values at lower concentrations and light intensities as examined from the first few data points depicted by Tanielian et al 94 It is not within the scope of this work to evaluate such effects, but our (low concentration) data set reflects a value of 0.57 for Φ Ru(bpy)3 Δ quite well.…”

Chemistry for the analysis of protein–protein interactions: Rapid and efficient cross-linking triggered by long wavelength light

“…An Ϸ20-fold lower yield was observed in the absence of APS, demonstrating the requirement of Ru(III) and͞or the sulfate radical for efficient cross-linking. Photoexcited Ru(bpy) 3 2ϩ is known to be an efficient generator of singlet oxygen (31,32), which is expected to be the dominant reaction in the absence of APS. Not surprisingly, this pathway also yields cross-linked products (see Fig.…”

Porphyrins Encapsulated into Pluronic F127 Micelles: Evaluating the Effect of the Central Metal and Substituents on the Photophysicochemical Properties in Water

“…where Ф Δ Std is the singlet oxygen quantum yield for the standard (H 2 TSPP) in water (=0.51), [20] W and W Std are the ADMA photobleaching rates in the presence of porphyrin derivatives under investigation and the standard, respectively. I abs and I abs Std are the rates of light absorption by the porphyrin derivative and standard, respectively.…”