The four polymorphic modifications of the semiconductor dibenzo-tetrathiafulvalene

The organic semiconductor dibenzotetrathiafulvalene (DB-TTF) presents, at ambient conditions, four polymorphic modifications. In addition to the already known monoclinic structure (alpha) with Z = 2, we have resolved by single crystal X-ray diffraction (XRD) a second crystal structure (beta), also monoclinic but with Z = 4. Two other polymorphic modifications (gamma and delta) have been found by means of lattice phonon confocal Raman microscopy and XRD. In this paper we present a series of growth experiments, from vapour or from solution, in films and in the bulk phase, describing the variety of transformations which occur among the different phases and their mixing, also at a micrometric scale. Quasi harmonic lattice dynamics calculations satisfactorily reproduce the structures of the alpha and the beta polymorphs and help the phonon assignment of polarized Raman spectra in single crystals.