Quenching of singlet oxygen ( 1Δ g) by cobalt complexes with four nitrogen atoms in the equatorial plane

• Published in: Journal of photochemistry and photobiology. B, Biology Vol. 58; no. 2; pp. 143 - 148
• Main Authors: Baranyai, Péter, Vidóczy, Tamás
• Format: Journal Article
• Language: English
• Published: Switzerland Elsevier B.V 01.11.2000
• Subjects: Cobalt - chemistry; Cobalt - radiation effects; Cobalt complex; Diffusion controlled reaction; Models, Molecular; Nitrogen - chemistry; Organometallic Compounds - chemistry; Organometallic Compounds - radiation effects; Oxygen - chemistry; Oxygen - radiation effects; Photochemistry; Quenching; Singlet Oxygen; Solvents; Singlet oxygen; Cobalt complex; Diffusion controlled reaction; Quenching
• ISSN: 1011-1344; 1873-2682
• DOI: 10.1016/S1011-1344(00)00119-6

The quenching of singlet oxygen ( 1Δ g) by cobalt(III)- bis-1,2-benzosemiquinone-diiminato complexes (general structure LCo (III)(BQDI) 2ClO 4) has been studied in different solvents by measuring the singlet oxygen phosphorescence decay in time-resolved experiments. The axial ligand (Ph 3As, Ph 3Sb, N-methyl-imidazole, pyrrolidine) has practically no influence on the quenching; however, the chlorinated benzosemiquinone-diiminato complex has a markedly lower quenching rate constant. The solvent effects can be fully explained by the difference in viscosity, which supports the assumption that the quenching is diffusion controlled. The reactive radius of the encounter pair has been estimated to be 0.3 nm, shorter than the radius of the complex itself, which points to the fact that singlet oxygen must approach the central cobalt atom at the (partially) open axial position. The significance of these results regarding the quenching of singlet oxygen by vitamin B 12 derivatives is discussed.