ISSN:
0894-3230
Schlagwort(e):
Organic Chemistry
;
Physical Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
The electron-transfer quenching of Ru(bpy)32+ (tris(2,2′-bipyridine)ruthenium(II) excited state by 2,4-dichlorophenol (2,4-DCP), 2,5-dichlorophenol (2,5-DCP) and 2,6-dichlorophenol (2,6-DCP), in their anionic forms, was studied in de-aerated solutions of neat methanol and 25, 50 and 75% v/v aqueous methanol at 30°C. The quenching rate constants (kq) were determined and their values range from 1 × 107 to 8 × 109 M-1 s-1. In all the mixtures methanol : water the kq values for 2,5-DCP were lower than for 2,4-DCP and 2,6-DCP. This result was discussed in terms of the effect of chloro atom on the quencher oxidation reaction. The photoredox product Ru(bpy)3+ was observed by laser flash photolysis and its quantum yield (ΦRu(+)) calculated by using a comparative method with the formation of zinctetraphenylporphyrin triplet state. The yields of cage escape (Yce) for the different methanol/water mixtures were calculated from the obtained values of ΦRu(+)). Yce increases from 0·1-0·2 in 25% v/v aqueous methanol to 0·5-0·6 in neat methanol. This change of Yce with the solvent composition was discussed in terms of combined effects of viscosity and solvent cage on the rate constant of cage escape (k-d) and the rate constant for back electron-transfer to the ground state from geminate pair (kbc), respectively. The constants k-d were calculated with the Eigen equation. The constants kbc were estimated from Yce and k-d by applying a simplified reaction scheme. The kbc kbc values range from 3·2 × 109 to 1·3 × 1010 s-1.
Zusätzliches Material:
3 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/poc.610081103
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