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A Femtosecond Study of Excitation‐Wavelength Dependence of Solvation Dynamics in a Vesicle
Author(s) -
Sen Pratik,
Ghosh Subhadip,
Mondal Sudip Kumar,
Sahu Kalyanasis,
Roy Durba,
Bhattacharyya Kankan,
Tominaga Keisuke
Publication year - 2006
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.200600036
Subject(s) - solvation , excitation , femtosecond , fluorescence , chemistry , lipid bilayer , vesicle , relaxation (psychology) , analytical chemistry (journal) , wavelength , bilayer , chemical physics , molecule , stokes shift , materials science , optics , membrane , organic chemistry , physics , optoelectronics , laser , psychology , social psychology , biochemistry , quantum mechanics
The dependence of fluorescence and solvation dynamics of coumarin 480 (C480) in a dimyristoyl–phosphatidylcholine (DMPC) vesicle on excitation wavelength ( λ ex ) was studied with femtosecond fluorescence upconversion. The study revealed an ultrafast 1.5‐ps component of solvation that was not detected earlier. C480 exhibits pronounced red‐edge excitation shift (REES) by 10 nm in a DMPC vesicle. This is due to the microheterogeneity of the lipid vesicle. In lipids, the probe is distributed in different locations with varying static and dynamic electrostatic responses. Solvent relaxation becomes faster and the amount of dynamic Stokes shift decreases with increasing λ ex . For excitation at the red end ( λ ex =430 nm), the solvation time was found to be 1.5 ps. However, for excitation at the blue end, ( λ ex =390 nm), there are two substantially slower components of 250 and 2000 ps. It seems that for λ ex =390 nm, the major contribution to total emission is due to the probe (C480) molecules in the hydrophobic and restricted locations inside the lipid bilayer. Excitation at 430 nm preferentially selects the probe molecules in a highly mobile environment (water pool of the lipid).