Polymorphism in Vanadyl Phthalocyanine

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Abstract
Phase transitions in vanadyl phthalocyanine have been studied using differential scanning calorimetry, x-ray scattering and optical absorption spectroscopy. Three phases, I, II and III, were prepared by nonequilibrium vapour quenching, equilibrium crystal growth and melt quenching, respectively. Phase I is metastable and transforms thermally to Phase II. Both Phase II and Phase III are stable up to the melting point. Phase II has a triclinic crystal structure isostructural with SnPc and is prone to systematic disorder in the ac plane. The disorder enhances the optical absorption at 6500 Å. Attempts to account for the optical absorption spectra using simple dipole-dipole models have been unsuccessful although dimeric structures are suggested for all three phases.