title: Photochromism of spiropyran nanocrystals embedded in sol-gel matrices.
abstract: Spectroscopic and kinetic properties of a new photochromic medium, consisting of nanocrystals of spyropyran molecules (1,3-dihydro-1,3,3,5',6',pentamethyl-spiro[2H-indole-2,2'-[2H]pyrano [3,2-b]pyridinium] iodide) embedded in an organo-silicate sol-gel film, are presented and compared to microcrystals obtained by slow evaporation of a solvent. High photoconversion efficiencies for both kinds of crystals have been observed. In microcrystals, the photomerocyanine form absorbs at 570 nm with a fading rate of 5 h, in nanocrystals the photomerocyanine form absorbs at 535 nm with a fading rate of 41 h. Therefore, the crystalline structure of nanocrystals is different from the microcrystal one.
authors.affiliation: Laboratoire de Spectrométrie Physique, Université Joseph Fourier, CNRS, BP 87, 38402, St Martin d'Hères Cedex, France. spagnoli@spectro.ujf-grenoble.fr
authors.forename: Sylvie
authors.initials: S
authors.lastname: Spagnoli
authors.forename: Dominique
authors.initials: D
authors.lastname: Block
authors.forename: Estelle
authors.initials: E
authors.lastname: Botzung-Appert
authors.forename: Isabelle
authors.initials: I
authors.lastname: Colombier
authors.forename: Patrice L
authors.initials: PL
authors.lastname: Baldeck
authors.forename: Alain
authors.initials: A
authors.lastname: Ibanez
authors.forename: Anne
authors.initials: A
authors.lastname: Corval