title: Temperature dependence of anisotropy decay and solvation dynamics of coumarin 153 in gamma-cyclodextrin aggregates.
abstract: Effect of temperature on the fluorescence anisotropy decay and the ultraslow component of solvation dynamics of coumarin 153 (C153) in a gamma-cyclodextrin (gamma-CD) nanocavity are studied using a picosecond set up. The steady-state anisotropy (0.13 +/- 0.01) and residual anisotropy (0.14 +/- 0.01) in fluorescence anisotropy decay in an aqueous solution containing 7 microM C153 and 40 mM gamma-CD are found to be quite large. This indicates formation of large linear nanotube aggregates of gamma-CD linked by C153. It is estimated that >53 gamma-CD units are present in each aggregate. In these aggregates with rise in temperature, the average solvation time (<tau(s)>(obs)) decreases markedly from 680 ps at 278 K to 160 ps at 318 K. The dynamic Stokes shift is found to decrease from 800 cm(-1) at 278 K to 250 cm(-1) at 318 K. The fraction of dynamic Stokes shift (f(d)) detected in a picosecond set up is calculated using the Fee-Maroncelli procedure. The corrected solvation time (<tau(s)>(corr) = f(d)<(tau(s)>(obs)) displays an Arrhenius type temperature dependence. From the temperature variation, the activation energy and entropy of the solvation process are determined to be 12.5 kcal M(-1) and 28 cal M(-1) K(-1), respectively. The ultraslow component and its temperature dependence are ascribed to a dynamic exchange between bound and free water molecules.
authors.affiliation: Physical Chemistry Department, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.
authors.forename: Durba
authors.initials: D
authors.lastname: Roy
authors.forename: Sudip Kumar
authors.initials: SK
authors.lastname: Mondal
authors.forename: Kalyanasis
authors.initials: K
authors.lastname: Sahu
authors.forename: Subhadip
authors.initials: S
authors.lastname: Ghosh
authors.forename: Pratik
authors.initials: P
authors.lastname: Sen
authors.forename: Kankan
authors.initials: K
authors.lastname: Bhattacharyya
mesh_terms: D003374:Coumarins / Q000737:chemistry*; D005454:Fluorescence Polarization; D008956:Models, Chemical; D015394:Molecular Structure; D043942:Nanotubes; D012997:Solvents / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013501:Surface-Active Agents / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D047408:gamma-Cyclodextrins / Q000737:chemistry*
chemical_list: D003374:Coumarins; D012997:Solvents; D013501:Surface-Active Agents; C488877:coumarin 153; D047408:gamma-Cyclodextrins; D014867:Water