Singlet Oxygen Chemistry in Water. 2. Photoexcited Sensitizer Quenching by O2 at the Water- Porous Glass Interface

  • Giaimuccio J
  • Zamadar M
  • Aebisher D
 et al. 
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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 x 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 microseconds in water. Triplet O2 quenched the transient absorption of triplet 1*-ads; for samples containing 0.9 x 10(-6)-0.9 x 10(-8) mol 1 adsorbed per g PVG, the Stern-Volmer constant, K(D), 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 approximately 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.

Author-supplied keywords

  • Adsorption
  • Glass
  • Glass: chemistry
  • Models
  • Molecular
  • Molecular Structure
  • Oxygen
  • Oxygen: chemistry
  • Photosensitizing Agents
  • Photosensitizing Agents: chemistry
  • Porosity
  • Time Factors
  • Water
  • Water: chemistry

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Authors

  • Jovan M Giaimuccio

  • Matibur Zamadar

  • David Aebisher

  • Gerald J. Meyer

  • Alexander Greer

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