A new linear luminophore consisting of five conjugated units of oxazole, phenylene and a central benzothiadiazole fragment, 4,7-bis[4-(1,3-oxazol-5-yl)phenyl]-2,1,3-benzothiadiazole, has been synthesized and characterized. Needle-like single-crystal samples up to 10 mm in length were obtained by physical vapor transport. The crystal structure was determined at 95 K and 293 K using single-crystal X-ray diffraction. With decreasing temperature, the space group P21/n does not change, but the unit-cell volume of the crystal decreases. The presence of intra- and intermolecular hydrogen bonds was established. Melting parameters (T m = 305.5°C, ΔH m = 52.2 kJ mol−1) and the presence of a liquid-crystalline mesophase (T LC = 336.3°C, ΔH LC = 1.4 kJ mol−1) were determined by differential scanning calorimetry and in situ thermal polarization optical microscopy studies. The presence of linear chains of hydrogen bonds ensures high stability of the crystal structure in a wide temperature range. The luminophore is characterized by a large Stokes shift (5120–5670 cm−1) and a high quantum yield of fluorescence, reaching 96% in solutions (λmax = 517 nm) and 27% in thin crystalline films (λmax = 529 nm). The calculated absorption and emission spectra are in good agreement with the experimental data. Because of the excellent optical properties and high thermal stability, the new linear luminophore has great potential for application in organic photonics and optoelectronic devices.

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Crystals of linear oligophenyls p-nP (n is the number of phenyl groups) are of interest for organic electronics and photonics as effective blue emitters and scintillators. The surface properties and external conditions of the growth medium are the determining factors in the nucleation and formation of crystals. However, the crystallization processes of conjugated linear molecules are still understudied and there is practically no experimental data on the surface properties of solutions and crystals. At the same time, there are few studies in the literature on modeling the surface energy of the crystal faces of these substances [1]. This work presents the results of studying of the linear oligophenyls (n = 2..6) crystals growth from solutions and the vapor phase. In the approximation of the OPLS atomic force field method, the values of the surface energy of the (100), ( 010), (110), and (001) faces of the crystals are determined. Based on the data on the crystal structure and the obtained values of the surface energy of the faces, the morphology of the crystals is analyzed and their equilibrium shapes are predicted. Within the framework of the classical nucleation theory, the parameters of crystal nucleation under experimental conditions of growth from solutions and physical vapor transport are studied.