Singlet oxygen chemistry in water. 2. Photoexcited sensitizer quenching by O2 at the water-porous glass interface.
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.
Department of Chemistry and Material Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Jovan
J
Giaimuccio
Matibur
M
Zamadar
David
D
Aebisher
Gerald J
GJ
Meyer
Alexander
A
Greer
D000327:Adsorption; D005898:Glass / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D017319:Photosensitizing Agents / Q000737:chemistry*; D016062:Porosity; D013997:Time Factors; D014867:Water / Q000737:chemistry*
D017319:Photosensitizing Agents; D014867:Water; D010100:Oxygen