Free‐standing microcrystals of a fluorescent organic dye: Preparation and spectroscopic study

Abstract

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.

Dendrimer-Tuned Formation of Fluorescent Organic Microcrystals. Influence of Dye Hydrophobicity and Dendrimer Charge

“…This indicates that a proportion of additive is situated at the microcrystal surface. This behavior was also encountered with other additives such as poly(acrylamide) and calf thymus DNA . It can be noted that small molecules such as sodium acetate and 1,4-hexanediamine have little effect upon the reprecipitation kinetics.…”

“…Concerning neutral additives, the reprecipitation of 1 and 2 was accelerated in the presence of G4 glucose-persubstituted PAMAM dendrimers, but it was slightly slower than with charged macromolecules, the whole process being complete within 15 min and 2 h, respectively, with 2 × 10 -5 M dye and 5 × 10 -5 M dendrimer . In the presence of poly(acrylamide) (3.2 × 10 -2 M of terminal groups), the duration of the process was the same as in water alone . This was also the case in the presence of the sodium salt of poly(acrylic acid) when the pH of the solution was lowered to 2 by addition of hydrochloric acid, that is when the carboxylic groups of the macromolecule were protonated.…”

“…28 In the presence of poly(acrylamide) (3.2 × 10 -2 M of terminal groups), the duration of the process was the same as in water alone. 31 This was also the case in the presence of the sodium salt of poly-(acrylic acid) when the pH of the solution was lowered to 2 by addition of hydrochloric acid, that is when the carboxylic groups of the macromolecule were protonated. A strong acceleration is thus linked to the presence of charged groups on the additive.…”

“…This behavior was also encountered with other additives such as poly(acrylamide) and calf thymus DNA. 31 It can be noted that small molecules such as sodium acetate and 1,4-hexanediamine have little effect upon the reprecipitation kinetics. This underlines the importance of the macromolecular structure that strongly interacts with the colloid by means of multiple functional groups.…”

Processes of Molecular Transformations and Self-Organization of Chromenoacridines in Liquid Crystal Matrices

“…The shape of a crystal is determined by the structure of a molecule [13,14]. So, by different additives to the solution, the growing, shape, and sizes of crystals can be managed [15]. The orienting influence of the liquid crystal fosters the growing up of highly organized dye crystals of ultra small sizes [16], being very prospective materials in nanotechnologies.…”