Blue-Emitting Nanocrystals, Microcrystals, and Highly Oriented Nanofibers Prepared by Reprecipitation and Solvent Drop-Casting of 2-Phenyl-naphthoxazoles
Résumé
Three 2-phenyl-naphth[2,3-d]oxazole derivatives, one of them being unsubstituted (1) and the two others bearing a methyl (2) and a tert-butyl group (3) in the para position of the phenyl ring, were prepared. In the crystalline state, all compounds adopted a crossed-stacking mode that favors fluorescence emission. They emitted in the blue region and their photoluminescence quantum yield ranged between 25 and 59 %. The preparation of micro/nanoparticles by simple methods was optimized. By using a solvent-exchange method, the compounds readily gave microcrystals, the size and shape of which closely depend on the nature of the substituent, as well as nanocrystals that measured around 200 nm. The proportion of micro- and nanocrystals was modulated by the experimental conditions and the two populations could be separated by filtration for subsequent use. For unsubstituted compound 1, drop-casting from a solution in tetrahydrofuran spontaneously generated an array of parallel and almost perpendicularly oriented nanofibers that exhibited efficient waveguiding properties. Owing to their robustness, good solid-state optical properties, and to the simplicity of particle preparation, these naphthoxazole derivatives appear as promising candidates for the fabrication of blue-emitting tracers and nanofibers.