Diffusional constant fluorescence quenching

Indirect evidence for the formation of a complex intermediate in diffusional energy transfer processes may be provided by the measurement of kt from both donor quenching and acceptor sensitization at low temperatures where kQC kf = 1/T° in this case exciplex relaxation should reduce the quencher sensitization efficiency but leave the donor fluorescence quenching constant unchanged. 

Time resolved studies on dye molecules can help to elucidate the solvation dynamics and can give information on the time constants of diffusion of the ionic components of an RTIL [69-75], Time resolved fluorescence studies show the diffusional motion of the dissolved solutes [76], Luminescence quenching of fluorescent transition metal dyes by oxygen has been used in case of so-called core-shell soft-sphere ionic liquids [77] to monitor the oxygen permeability of these ILs [78],... 

Additionally, Hunter and coworker presented another model for the noncovalently linked donor-acceptor complex which was made up of triad components, quinone-cyclophane-porphyrin 144. H NMR measurements indicated the formation of a ternary complex and the association constant of BQ via hydrogen bonds was determined to be 1.4 x 10 M, while the association constant of pyridine of the cyclophane and zinc porphyrin was 3.2 X lO M in dichloromethane. The fluorescence emission from the zinc porphyrin in the presence of the cyclophane was clearly quenched by the addition of BQ, compared with a control experiment, due to diffusional quenching. This evidence indicated that the intracomplex ET occurred within the triad system. 

The foregoing metal complexes have served as donor-acceptor pairs in other, related systems, and these also demonstrate some aspects of the preceding rapid electron transfer (128). In a related study, the electron transfer between PBAC as the donor and tris(9,10-phenanthroline)Co(III) + (abbreviated Co(-phen)s +) as the electron acceptor was investigated. Even when just micromolar concentrations of the acceptor were intercalated in the galleries of BAZrP, the donor fluorescence was quenched very efficiently. The estimated quenching rate constant ( 3 X lO" dm mol s ) far exceeded the expected diffusional rate (69,120). 

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