Blue‐Emitting Nanocrystals, Microcrystals, and Highly Oriented Nanofibers Prepared by Reprecipitation and Solvent Drop‐Casting of 2‐Phenyl‐naphthoxazoles

Abstract

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.

Mechanofluorochromic Properties of an AIEE‐Active 2‐Phenylbenzoxazole Derivative: More than Meets the Eye?

“…The crystal unit cell contained two molecules. The PBO framework was planar, as already noticed for various derivatives of this compound and closely‐related 2‐phenylnaphthoxazole derivatives, and the dicyanovinyl group formed a small dihedral angle of around 11° with the rest of the molecule. Each molecule shared short contacts with six neighbours located on the same plane.…”

Naphth[1,2-d]imidazoles Bioactive from β-Lapachone: Fluorescent Probes and Cytotoxic Agents to Cancer Cells

“…The molar absorption coefficient (ε Abs ) is also an important parameter for the development of fluorescent probes. Samples prepared with naphth[1,2- d ]imidazoles IM1 – IM7 showed high ε Abs on the order of 10 3 to 10 4 M −1 cm −1 ( Table 1 ), which is consistent with the allowed transition π→π* of π-conjugated systems [ 26 , 28 , 29 , 30 ] characteristic of the imidazole nucleus [ 25 , 31 ].…”

Influence of the halogen atom on the solid-state fluorescence properties of 2-phenyl-benzoxazole derivatives

“…To increase the chances of developing highly fluorescent materials, a strategy is to work with the rare families of dyes that are not prone to plane-to-plane stacking. This is the case for the 4 0 -alkyl and 4 0 -alkoxy derivatives of 2-phenyl-benzoxazole [9] and naphthoxazole [10] that exhibit an original packing mode and display excellent fluorescence properties in the crystalline state. Our recent study revealed that small variations in the nature of the substituent borne by the phenyl ring lead to substantial changes in the spectroscopic and self-association properties.…”

“…The reprecipitation method is a mild method, based on solvent exchange. Primarily developed by Nakanishi and coworkers [39,40], it has proved to be very useful to us in preparing nano-and micro-crystals of various organic dyes [41e43], including benzoxazole and naphthoxazole dyes [9,10]. It generally consists in dissolving the organic compounds in a hydrophilic solvent, and then pouring a small volume of this concentrated solution into a large volume of water.…”