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Ultrafast electron transfer dynamics in micellar media using surfactant as the intrinsic electron acceptor.
MedLine Citation:
PMID:  20684629     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Abstract/OtherAbstract:
Ultrafast photoinduced intermolecular electron transfer (ET) dynamics involving 7-aminocoumarin derivatives as electron donor and pyridinium moiety of surfactant molecules in cetylpyridinium chloride (CPC) micelle as electron acceptor has been investigated to understand the role of separation and orientation of reactants on micellar ET reactions. Unlike in noninteracting micelles (like Triton-X-100, sodium dodecyl sulfate, dodecyltrimethylammonium bromide, etc.), where surfactant-separated donor-acceptor pairs are understood to give the ultrafast ET component with the shortest time constant in the range of approximately 4 ps, in CPC micelles with pyridinium moiety as the intrinsic acceptor the ultrafast ET component is found to be in the subpicosecond time scale (of around 240 fs). This time scale is very similar to the values reported in the cases of ultrafast ET reactions involving coumarin dyes in electron-donating solvents. The ultrafast ET times in CPC micelles are significantly faster than the diffusive solvation dynamics in the micellar media. Correlation of the observed ET rates in the present cases with the free-energy changes of the reactions shows the inverse-bell-shaped correlation, predicted by Marcus ET theory. Interestingly, the onset of the Marcus inversion appears at a relatively lower exergonicity, which is attributed to the nonequilibrium solvent configuration during the ultrafast ET reaction, as envisaged from two-dimensional ET (2DET) model. Along with the ultrafast ET component, there are also slower ET components in these systems, which are attributed to those close-contact donor-acceptor populations in the micelles that have relatively weaker electronic coupling due to improper orientation of the interacting donor-acceptor pairs. The present results suggest that, along with the shifting of Marcus inversion at lower exergonicity, the ET rates can also be maximized in a micellar media by using surfactant molecule as an intrinsic reactant.
Authors:
Manoj Kumbhakar; Prabhat Kumar Singh; Ashis Kumar Satpati; Sukhendu Nath; Haridas Pal
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  The journal of physical chemistry. B     Volume:  114     ISSN:  1520-5207     ISO Abbreviation:  J Phys Chem B     Publication Date:  2010 Aug 
Date Detail:
Created Date:  2010-08-05     Completed Date:  2010-11-29     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101157530     Medline TA:  J Phys Chem B     Country:  United States    
Other Details:
Languages:  eng     Pagination:  10057-65     Citation Subset:  -    
Affiliation:
Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India. manojk@barc.gov.in
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