Phase recognition by lattice phonon Raman spectra: the triclinic structure of the organic semiconductor dibenzo-tetrathiafulvalene.

We present a working example of phase recognition by lattice phonon Raman spectroscopy, a technique which has proved to be a powerful tool for identifying new polymorphs. The spectra show that a newly resolved triclinic structure of the organic semiconductor dibenzo-tetrathiafulvalene (DB-TTF) is one of its four polymorphic modifications, labeled the δ-phase, which was previously identified only from spectroscopic data. The now available XRD data allow for the computation of the minimum potential energy structure. Calculated density and energy of the triclinic polymorph are found to be very close to the previously identified β polymorph. These similarities account for the often encountered co-existence of the β and δ crystal phases.