Tetracene Crystals: Growth from Solutions, Solubility, and Thermal Properties

The solubility of tetracene crystals has been investigated experimentally and theoretically within the approximation of regular-solution model. The grown crystals had a shape of thin elongated plates. The largest tetracene crystal (8 mm × 50 μm in size) was grown from a benzene solution by precipitant vapor diffusion into solution. The X-ray diffraction pattern from a developed crystal face is the result of the X-ray beam reflection from the (001) plane of a set of monolayers with a thickness d 001 = 1.21 nm. An analysis of the surface morphology of the (001) face of tetracene crystal by atomic force microscopy (AFM) revealed the presence of elementary growth steps, whose height coincides (within the measurement error) with the monolayer thickness d 001 . The parameters of melting ( T m = 343.0°C, Δ H m = 35.6 kJ/mol) and polymorphic transition ( T tr =310.0°C, Δ H tr = 0.9 kJ/mol) of tetracene were refined using differential scanning calorimetry (DSC). A comparison of the optical absorption and luminescence spectra of solutions of a pure tetracene sample and a processed (previously molten in a hermetic crucible in an inert atmosphere) sample in toluene confirms degradation of the material subjected to overheating above the melting temperature.