title: Analysis of the Photophysical Behavior and Rotational-Relaxation Dynamics of Coumarin 6 in Nonionic Micellar Environments: The Effect of Temperature.
abstract: The photodynamics of Coumarin 6 have been investigated in three nonionic micellar assemblies, i.e., n-dodecyl-β-D-maltoside (β-C12G₂), p-tert-octyl-phenoxy polyethylene (9.5) ether (Triton X-100 or TX100) and n-dodecyl-hexaethylene-glycol (C12E₆), to assess their potential use as encapsulation vehicles for hydrophobic drugs. To evaluate the effect of the micellar size and hydration, the study used a broad temperature range (293.15-323.15 K). The data presented here include steady-state absorption and emission spectra of the probe, dynamic light scattering, together with fluorescence lifetimes and both steady-state, as well as time-resolved fluorescence anisotropies. The time-resolved fluorescence anisotropy data were analyzed on the basis of the well-established two-step model. Our data reveal that the molecular probe in all of the cases is solubilized in the hydration layer of micelles, where it would sense a relatively polar environment. However, the probe was found to undergo a slower rotational reorientation when solubilized in the alkylpolyglycoside surfactant, as a result of a more compact microenvironment around the probe. The behavior of the parameters of the reorientation dynamics with temperature was analyzed on the basis of both micellar hydration and the head-group flexibility of the surfactants.
authors.affiliation: Department of Applied Physics II, Engineering School, University of Malaga, Malaga 29071, Spain. ccarnero@uma.es.
authors.forename: Cristóbal Carnero
authors.initials: CC
authors.lastname: Ruiz
authors.affiliation: Department of Applied Physics II, Engineering School, University of Malaga, Malaga 29071, Spain. jose.hierrezuelo80@gmail.com.
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Hierrezuelo
authors.affiliation: Department of Applied Physics II, Engineering School, University of Malaga, Malaga 29071, Spain. jmb@uma.es.
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Molina-Bolivar
mesh_terms: D004396:Coloring Agents; D003374:Coumarins / Q000737:chemistry*; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D008968:Molecular Conformation; D010316:Particle Size; D013696:Temperature; D013844:Thiazoles / Q000737:chemistry*; D014783:Viscosity
chemical_list: D004396:Coloring Agents; D003374:Coumarins; D005456:Fluorescent Dyes; D008823:Micelles; D013844:Thiazoles; C517282:coumarin 6
keywords: Coumarin 6; Triton X-100; n-dodecyl-hexaethylene-glycol; n-dodecyl-β-d-maltoside; nonionic micellar assemblies; time-resolved fluorescence anisotropy