title: Efficient sensing of explosives by using fluorescent nonporous films of oligophenyleneethynylene derivatives thanks to optimal structure orientation and exciton migration.
abstract: The fluorescence of thin films of a diimine-substituted phenyleneethynylene compound can be efficiently quenched by nitroaromatic vapors, which is not the case for the unsubstituted parent compound. Thin-film porosity is usually considered to be an essential factor for efficient quenching, but in the present case the origin of the quenching is completely different, as both films are nonporous and hermetic to 2,4-dinitrotoluene (DNT) molecules. The molecular organization in the two crystallized thin films offers a low level of π stacking for both compounds, but the orientation of the phenylenethynylene fluorophore differs markedly with respect to the surface of the films. For the substituted compound, the fluorophore is almost parallel to the surface, thus making it readily available to molecules of a nitroaromatic quencher. This rationale is also observed in the case of a related compound bearing methoxy side chains instead of the long octyloxy moieties. Fluorescence-lifetime experiments show that the efficient quenching process in the nonporous crystallized films of the substituted compound is due to a fast (<70 ps) diffusion of excitons from the bulk of the film toward the surface where they are quenched, thus providing evidence of antenna effects.
authors.affiliation: CEA-DAM Le Ripault, BP 16, 37260 Monts (France), Fax: (+33) 247345142.
authors.forename: Thomas
authors.initials: T
authors.lastname: Caron
authors.forename: Eric
authors.initials: E
authors.lastname: Pasquinet
authors.forename: Arie
authors.initials: A
authors.lastname: van der Lee
authors.forename: Robert B
authors.initials: RB
authors.lastname: Pansu
authors.forename: Vincent
authors.initials: V
authors.lastname: Rouessac
authors.forename: Simon
authors.initials: S
authors.lastname: Clavaguera
authors.forename: Myriam
authors.initials: M
authors.lastname: Bouhadid
authors.forename: Françoise
authors.initials: F
authors.lastname: Serein-Spirau
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Lère-Porte
authors.forename: Pierre
authors.initials: P
authors.lastname: Montméat
keywords: photoluminescence; sensors; structure-property relationships; supramolecular materials; surfaces and interfaces; thin films