Raman investigation of polymorphism in 1,1,4,4-tetraphenyl-butadiene

We present a Raman investigation of polymorphism in 1,1,4,4-tetraphenyl-butadiene (TPB), a well-known blue luminescent molecule, which retains its emissive properties in the solid state. The use of low-wavenumber (10-150 cm-1) Raman microscopy, very sensitive to the crystal packing, allows us to single and pick up four different polymorphs. X-ray analysis shows that the TPB molecules assume different conformations in the various polymorphs, a fact revealed also by the Raman spectra in the region of intra-molecular vibrations. Lattice dynamics calculations yield a preliminary assignment of the low-wavenumber Raman spectra and provide information of the relative stability of the phases