title: Effects of DNA on the growth and optical properties of luminescent organic microcrystals.
abstract: The reprecipitation method, which is a solvent-exchange process, was used to prepare free-standing microcrystals from an organic fluorescent dye, 4-n-octylamino-7-nitrobenz-2-oxa-1,3-diazole. Calf thymus DNA was introduced as an additive into the reprecipitation medium, strongly accelerating the process. The reprecipitation kinetics was monitored by UV/vis absorption spectroscopy, and the analysis of the rate constants allowed the role played by the additive to be clarified. DNA was also found to affect the shape and size of the dye microcrystals obtained. In particular, its presence induced the formation of a new type of microcrystal that displays original two-color fluorescence. The emission properties were first analyzed on the suspensions, using a traditional fluorimeter, and then on individual microcrystals by means of a space- and time-correlated photon-counting photomutiplier installed on a microscope. The study on single microcrystals suggests that the dual coloration observed originates from the reabsorption of the blue component of the emitted light, whereas the remaining red component propagates through the microcrystal body and is scattered by the edges. However, the color of the other types of microcrystals can be explained only by specific arrangements of molecules at the surface of the crystal.
authors.affiliation: Laboratoire des Interactions Moléculaires Réactivité Chimique et Photochimique, UMR CNRS 5623, Université Paul Sabatier, 31062 Toulouse Cedex 9, France.
authors.forename: Liliana
authors.initials: L
authors.lastname: Bîrla
authors.forename: Franck
authors.initials: F
authors.lastname: Bertorelle
authors.forename: Fernanda
authors.initials: F
authors.lastname: Rodrigues
authors.forename: Sophie
authors.initials: S
authors.lastname: Badré
authors.forename: Robert
authors.initials: R
authors.lastname: Pansu
authors.forename: Suzanne
authors.initials: S
authors.lastname: Fery-Forgues
mesh_terms: D000818:Animals; D002417:Cattle; D003460:Crystallization; D004247:DNA / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D008163:Luminescent Measurements; D010069:Oxadiazoles / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D010069:Oxadiazoles; D004247:DNA; C427203:calf thymus DNA