Document Type

Article

Publication Date

2008

Abstract

Insight into the O2 quenching mechanism of a photosensitizer (static or dynamic) would be useful for the design of heterogeneous systems to control the mode of generation of 1O2 in water. Here, we describe the use of a photosensitizer, meso-tetra(N-methyl-4-pyridyl)porphine (1), which was adsorbed onto porous Vycor glass (PVG). A maximum loading of 1.1 × 10−6 mol 1 per g PVG was achieved. Less than 1% of the PVG surface was covered with photosensitizer 1, and the penetration of 1 reaches a depth of 0.32 mm along all faces of the glass. Time-resolved measurements showed that the lifetime of triplet 1*-ads was 57 μs in water. Triplet O2 quenched the transient absorption of triplet 1*-ads; for samples containing 0.9 × 10−6−0.9 × 10−8 mol 1 adsorbed per g PVG, the Stern−Volmer constant, KD, ranged from 23 700 to 32 100 M−1. The adduct formation constant, KS, ranged from 1310 to 510 M−1. The amplitude of the absorption at 470 nm decreased slightly (by about 0.1) with increased O2 concentrations. Thus, the quenching behavior of triplet 1*-ads by O2 was proposed to be strongly dependent on dynamic quenching. Only ∼10% of the quenching was attributed to the static quenching mechanism. The quenching of triplet 1*-ads was similar to that observed for photosensitizers in homogeneous solution which are often quenched dynamically by O2.

Comments

"Reprinted (adapted) with permission from (Jovan Giaimuccio; Matibur Zamadar; David Aebisher; Gerald J. Meyer; Alexander Greer “Singlet Oxygen Chemistry in Water. 2. Photophysics of Quenching of a Photosensitizer by O2 at the Water/Porous Glass Interface” J. Phys. Chem. B 2008, 112, 15646-15650.) Copyright (2008) American Chemical Society."

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