Spectroscopic and Structural Characterization of Two Polymorphsof 1,1,4,4-Tetraphenyl-1,3-butadiene

We report a combined spectroscopic and structural study of polymorphism of 1,1,4,4-tetraphenyl-1,3- butadiene (TPB) blue luminescent crystals. We have identified two polymorphs, which can be grown by crystallization of the vapor. The first, R-TPB, has the monoclinic noncentrosymmetric structure (P21, two molecules per unit cell), whose lattice parameters have already been reported in the literature. The second, β-TPB, is a new polymorph, monoclinic centrosymmetric (P21/c, four molecules per unit cell). The previously reported triclinic structure, γ-TPB, has not been identified in samples grown by the physical vapor transport method. The effects of the different molecular configuration and packing of Rand β-TPB on Raman scattering, IR, and UV-vis optical properties are discussed.