ENHANCEMENT OF THE SENSITIVITY OF RADIATIVE and NON‐RADIATIVE DETECTION TECHNIQUES IN THE STUDY OF PHOTOSENSITIZATION BY WATER SOLUBLE SENSITIZERS USING A REVERSE MICELLE SYSTEMS*,†

Abstract

The study of photosensitization processes in aqueous solution is complicated by the unsuit‐ability of water as solvent for the commonly used techniques for monitoring radiative and non‐radiative relaxation processes. The infrared luminescence method is hampered by the relatively weak intensity of emission and short lifetime of singlet molecular oxygen, O2(1Δg), in water. Photoacoustic and photothermal detection of the dominant non‐radiative relaxation process for O2(1Δg) is also inhibited by the unfavorable physico‐chemical properties of water which reduce the sensitivities of these techniques for the study of sensitizers in aqueous with respect to non‐aqueous media. Such problems have been alleviated by incorporating the sensitizer in the aqueous core of aerosol OT reverse micelles. It is demonstrated that the sensitivity of both radiative and non‐radiative detection depends not on the local environment of the sensitizer but on the overall composition of the medium, which, in the case of reverse micelle solutions, is predominantly hydrocarbon. This produces a 4.5 and 6‐fold enhancement of the sensitivity of luminescence and optoacoustic detection, respectively, in comparison to purely aqueous solution. The utility of the method is demonstrated for Rose Bengal, where quantum yields of intersystem crossing (φisc) of 0.78 (LIOAC) and singlet oxygen generation (φδ) of 0.81 (LIOAC) and 0.80 (TRLD) were measured. Phenazine was also studied for comparative purposes and to corroborate values obtained for Rose Bengal.

Singlet Molecular Oxygen Quenching Ability of Carotenoids in a Reverse-micelle Membrane Mimetic System¶

“…where τ= k d −1 is the O 2 ( 1 Δ g ) lifetime, and I o refers to the amplitude of the signal at “zero” time, which is proportional to the quantum yield of O 2 ( 1 Δ g ) production, Φ Δ (50). Redmond (51) has reported Φ Δ = 0.8 for RB in AOT reverse micelle systems, which is close to that observed in homogeneous solvents (5). Under the same experimental conditions we did not observe significant difference in the I o values observed between 5 ≤ W ≤ 50, indicating that Φ Δ remains almost constant or that the quencher does not consume the sensitizer (or both).…”

Design and Properties of Porphyrin‐based Singlet Oxygen Generator

“…The environmental conditions of photosensitizers is a crucial issue for 1 O 2 generation 33. Water‐soluble tricationic porphyrin conjugates ( 6a , 6b , and 6c ; Figure 8) bearing dicyclohexylurea and galactopyranosyl groups were prepared by Silva et al.…”

Singlet oxygen quantum yields of potential porphyrin-based photosensitisers for photodynamic therapy

“…10 Once produced singlet oxygen can relax by radiative, non-radiative or quenching processes. The emission spectroscopic method, 11-14 calorimetric methods, (in particular laser-induced opto-acoustic calorimetry), [14][15][16] time resolved thermal lensing, [17][18][19] and chemical quenching experiments 16,20, 21 have been used for monitoring singlet oxygen formation. Large discrepancies in the reported values of singlet oxygen quantum yields have been attributed to the differing methods used for determining this value.…”