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Title: Effect of micellar environment on Marcus correlation curves for photoinduced bimolecular electron transfer reactions

Abstract

Photoinduced electron transfer (ET) between coumarin dyes and aromatic amine has been investigated in two cationic micelles, namely, cetyltrimethyl ammonium bromide (CTAB) and dodecyltrimethyl ammonium bromide (DTAB), and the results have been compared with those observed earlier in sodium dodecyl sulphate (SDS) and triton-X-100 (TX-100) micelles for similar donor-acceptor pairs. Due to a reasonably high effective concentration of the amines in the micellar Stern layer, the steady-state fluorescence results show significant static quenching. In the time-resolved (TR) measurements with subnanosecond time resolution, contribution from static quenching is avoided. Correlations of the dynamic quenching constants (k{sub q}{sup TR}), as estimated from the TR measurements, show the typical bell-shaped curves with the free-energy changes ({delta}G{sup 0}) of the ET reactions, as predicted by the Marcus outersphere ET theory. Comparing present results with those obtained earlier for similar coumarin-amine systems in SDS and TX-100 micelles, it is seen that the inversion in the present micelles occurs at an exergonicity (-{delta}G{sup 0}>{approx}1.2-1.3 eV) much higher than that observed in SDS and TX-100 micelles (-{delta}G{sup 0}>{approx}0.7 eV), which has been rationalized based on the relative propensities of the ET and solvation rates in different micelles. In CTAB and DTAB micelles, the k{sub q}{sup TR} valuesmore » are lower than the solvation rates, which result in the full contribution of the solvent reorganization energy ({lambda}{sub s}) towards the activation barrier for the ET reaction. Contrary to this, in SDS and TX-100 micelles, k{sub q}{sup TR} values are either higher or comparable with the solvation rates, causing only a partial contribution of {lambda}{sub s} in these cases. Thus, Marcus inversion in present cationic micelles is inferred to be the true inversion, whereas that in the anionic SDS and neutral TX-100 micelles are understood to be the apparent inversion, as envisaged from two-dimensional ET theory.« less

Authors:
; ; ;  [1]
  1. Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India)
Publication Date:
OSTI Identifier:
20722998
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 123; Journal Issue: 3; Other Information: DOI: 10.1063/1.1953579; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AMINES; AROMATICS; BROMIDES; COUMARIN; ELECTRON TRANSFER; EV RANGE 01-10; FLUORESCENCE; FREE ENERGY; MILLI EV RANGE; PHOTOCHEMISTRY; QUENCHING; TIME RESOLUTION

Citation Formats

Kumbhakar, Manoj, Nath, Sukhendu, Mukherjee, Tulsi, and Pal, Haridas. Effect of micellar environment on Marcus correlation curves for photoinduced bimolecular electron transfer reactions. United States: N. p., 2005. Web. doi:10.1063/1.1953579.
Kumbhakar, Manoj, Nath, Sukhendu, Mukherjee, Tulsi, & Pal, Haridas. Effect of micellar environment on Marcus correlation curves for photoinduced bimolecular electron transfer reactions. United States. https://doi.org/10.1063/1.1953579
Kumbhakar, Manoj, Nath, Sukhendu, Mukherjee, Tulsi, and Pal, Haridas. 2005. "Effect of micellar environment on Marcus correlation curves for photoinduced bimolecular electron transfer reactions". United States. https://doi.org/10.1063/1.1953579.
@article{osti_20722998,
title = {Effect of micellar environment on Marcus correlation curves for photoinduced bimolecular electron transfer reactions},
author = {Kumbhakar, Manoj and Nath, Sukhendu and Mukherjee, Tulsi and Pal, Haridas},
abstractNote = {Photoinduced electron transfer (ET) between coumarin dyes and aromatic amine has been investigated in two cationic micelles, namely, cetyltrimethyl ammonium bromide (CTAB) and dodecyltrimethyl ammonium bromide (DTAB), and the results have been compared with those observed earlier in sodium dodecyl sulphate (SDS) and triton-X-100 (TX-100) micelles for similar donor-acceptor pairs. Due to a reasonably high effective concentration of the amines in the micellar Stern layer, the steady-state fluorescence results show significant static quenching. In the time-resolved (TR) measurements with subnanosecond time resolution, contribution from static quenching is avoided. Correlations of the dynamic quenching constants (k{sub q}{sup TR}), as estimated from the TR measurements, show the typical bell-shaped curves with the free-energy changes ({delta}G{sup 0}) of the ET reactions, as predicted by the Marcus outersphere ET theory. Comparing present results with those obtained earlier for similar coumarin-amine systems in SDS and TX-100 micelles, it is seen that the inversion in the present micelles occurs at an exergonicity (-{delta}G{sup 0}>{approx}1.2-1.3 eV) much higher than that observed in SDS and TX-100 micelles (-{delta}G{sup 0}>{approx}0.7 eV), which has been rationalized based on the relative propensities of the ET and solvation rates in different micelles. In CTAB and DTAB micelles, the k{sub q}{sup TR} values are lower than the solvation rates, which result in the full contribution of the solvent reorganization energy ({lambda}{sub s}) towards the activation barrier for the ET reaction. Contrary to this, in SDS and TX-100 micelles, k{sub q}{sup TR} values are either higher or comparable with the solvation rates, causing only a partial contribution of {lambda}{sub s} in these cases. Thus, Marcus inversion in present cationic micelles is inferred to be the true inversion, whereas that in the anionic SDS and neutral TX-100 micelles are understood to be the apparent inversion, as envisaged from two-dimensional ET theory.},
doi = {10.1063/1.1953579},
url = {https://www.osti.gov/biblio/20722998}, journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 3,
volume = 123,
place = {United States},
year = {Fri Jul 15 00:00:00 EDT 2005},
month = {Fri Jul 15 00:00:00 EDT 2005}
}