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Sensitized photo‐redox reaction: VII. The Synthesis, FAB mass spectrum, stationary absorption, emission, transient absorption spectra, redox potential of dihydroxy‐tin (IV)‐mesoporphyrin dimethyl ester and its sensitized photo‐reduction of methyl viologen
Author(s) -
Liang XiaoGuang,
Leung HiuKwong,
Wu GuoZhang,
Hu Ming,
Yu Qun,
Shou HanSen,
Yan Lin,
Liang XiYun
Publication year - 1989
Publication title -
acta chimica sinica english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 0256-7660
DOI - 10.1002/cjoc.19890070314
Subject(s) - chemistry , redox , photochemistry , flash photolysis , quenching (fluorescence) , triplet state , absorption spectroscopy , phosphorescence , quantum yield , ultrafast laser spectroscopy , reaction rate constant , fluorescence , inorganic chemistry , spectroscopy , organic chemistry , kinetics , physics , quantum mechanics , molecule
In DMSO/water (4:1), photolysis of the dihydroxy‐Sn (IV)‐mesoporphyrin dimethyl ester (SnP)/methyl viologen (MV 2+ )/ethylene diamine tetraacetic acid (EDTA) ternary system produces methyl viologen cation radical with a quantum yield of 0.67, much higher than that of systems with other metal complexes of mesoporphyrin dimethyl ester. Neither EDTA nor MV 2+ quenches the stationary fluorescence of SnP, implying that the reaction does not take place at the singlet state. With flash photolysis we obtain the T‐T absorption spectrum of SnP (λ max 440 nm). By following the decay of this absorption, the triplet life time of SnP is estimated to be 41 μs. The life time is related to the concentration of either MV 2+ or EDTA. Good linear relationships are obtained by plotting τ 0 τ vs. the concentration of MV 2+ or EDTA (Stern‐Volmer plot), from which we determine the quenching constants: k q (MV 2+ ) =5.5 × 10 7 mol −1 , s −1 ; k q (EDTA) =2.7 × 10 7 mol −1 , s −1 . The data suggests that upon photolysis of the above ternary system, both oxidative quenching and reductive quenching of the triplet state of the sensitizer are occurring. From the measured phosphorescence spectrum (λ max 704 nm) and the ground state redox, potentials ( E red 1/2 ˜‐0.84V, E ox 1/2 ˜+1.43 V, vs. Ag/AgCl, KCl (sat.)), we obtain the redox potential of triplet SnP to be E (P + /P* T )˜‐0.33 V, E (P* T +/P − )˜+0.92 V. Matching this data with the redox potential of MV 2+ and EDTA, we establish the fact that during the photolysis of the SnP/MV 2+ /EDTA ternary system, both oxidative and reductive quenching are thermodynamically favorable processes. This is also the reason why the SnP sensitized reaction is much more efficient relative to other mesoporphyrin derivatives.