title: Photophysics of calixarenes bearing two or four dansyl fluorophores: charge, proton and energy transfers.
abstract: The photophysical properties of calixarenes bearing two and four dansyl derivatives (Calix-DANS2 and Calix-DANS4) were investigated in a CH(3)CN/H(2)O mixture (60 : 40 v/v). The carboxydansyl (DANS1) was used as a reference compound. The pH titration of DANS1 permits determination of two pK(A) values (2.4 and 6.3). The charge-transfer character of this type of fluorophore is discussed. The protonated dansyl group LH(2)(+) undergoes photoinduced proton transfer. The photophysical characterization (absorption spectra, emission spectra, quantum yield and fluorescence decays) of Calix-DANS2 and Calix-DANS4 showed that nonradiative energy transfer occurs from a dansyl fluorophore in the basic form to another one in the neutral form. The transfer efficiencies are 0.1 and 0.5 for Calix-DANS2 and Calix-DANS4, respectively. Fluorescence data analysis allowed us to determine the fractions of dansyl fluorophores in the basic and neutral forms.
authors.affiliation: CNRS UMR 8531 Laboratoire de Photophysique et Photochimie Supramoléculaires et Macromoléculaires, Département de Chimie, ENS-Cachan, 61 Avenue du Président Wilson, F-94235 Cachan Cedex, France.
authors.forename: Rémi
authors.initials: R
authors.lastname: Métivier
authors.forename: Isabelle
authors.initials: I
authors.lastname: Leray
authors.forename: Bernard
authors.initials: B
authors.lastname: Valeur