Free-standing microcrystals of a fluorescent organic dye: preparation and spectroscopic study

Suspensions of microcrystals were obtained from an organic fluorescent dye, 4- n -octylamino-7-nitrobenz-2-oxa-1,3-diazole, by reprecipitation in water in the presence of various macromolecules: anionic or cationic PAMAM dendrimer, poly(acrylic acid, sodium salt), poly(acrylamide), and calf thymus DNA. The use of these additives allowed the size and shape of the microcrystals to be controlled. A study by UV/vis absorption and fluorescence spectroscopy revealed some common points, but also some interesting differences, in the optical behaviour of the five samples.