A femtosecond study of excitation wavelength dependence of solvation dynamics in a PEO-PPO-PEO triblock copolymer micelle

Abstract

Excitation wavelength (lambdaex) dependence of solvation dynamics of coumarin 480 (C480) in the micellar core of a water soluble triblock copolymer, PEO20-PPO70-PEO20 (Pluronic P123), is studied by femtosecond and picosecond time resolved emission spectroscopies. In the P123 micelle, the width of the emission spectrum of C480 is found to be much larger than that in bulk water. This suggests that the P123 micelle is more heterogeneous than bulk water. The steady state emission maximum of C480 in P123 micelle shows a significant red edge excitation shift by 25 nm from 453 nm at lambdaex=345 nm to 478 nm at lambdaex=435 nm. The solvation dynamics in the interior of the triblock copolymer micelle is found to depend strongly on the excitation wavelength. The excitation wavelength dependence is ascribed to a wide distribution of locations of C480 molecules in the P123 micelle with two extreme environments-a bulklike peripheral region with very fast solvent response and a very slow core region. With increase in lambdaex, contribution of the bulklike region having an ultrafast component (< or =2 ps) increases from 7% at lambdaex=375 nm to 78% at lambda(ex)=425 nm while the contribution of the ultraslow component (4500 ps) decreases from 79% to 17%.

Ultrafast fluorescence resonance energy transfer in a bile salt aggregate: Excitation wavelength dependence

“…For organic molecules in a micelle the translational diffusion D t is of the order 0⋅5-50 Å 2 /ns. [14][15][16] For 105 mM NaDC aggregate the ultrafast component of FRET: 4 ps and the long 3700 ps component correspond to diffusion lengths of 1⋅3 Å and 38⋅5 Å, respectively. Obviously, diffusion of donors in the 4 ps time scale of FRET is smaller than molecular dimensions.…”

Ultrafast Dynamics in Biological Systems and in Nano-Confined Environments

“…20 Contribution of the of 60 ps component, which arises from chain dynamics, decreases from 14% at ex ¼ 375 nm to 5% at ex ¼ 425 nm. 20 …”

“…Sen et al studied solvation dynamics in different regions of a P123 micelle by varying ex . 20 With increase in ex from 375 to 478 nm, the emission maximum of C480 exhibits a large red edge excitation shift (REES) by 25 nm.…”

The thermochromism of the ET(30) betaine in a micro-heterogeneous medium: A spectral and dynamics simulation study

“…The temperature-dependent formation of polymeric micelles in water is well-documented, and has been studied with a variety of techniques [16][17][18][19][20][21]. Among them, various research groups have employed dyes and fluorescent probes for the study of the micellization process and for assessing the polarity of the heterogeneous microenvironment of these surfactant solutions [22][23][24][25][26][27][28].…”