Sandra Ianelli

Publications (2)3.41 Total impact

• Article: Spectroscopic and Structural Characterization of Two Polymorphs of 1,1,4,4-Tetraphenyl-1,3-butadiene

  Alberto Girlando, Sandra Ianelli, Ivano Bilotti, Aldo Brillante, Raffaele G. Della Valle, Elisabetta Venuti, Marcello Campione, Stefano Mora, Leonardo Silvestri, Peter Spearman, Silvia Tavazzi
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  ABSTRACT: 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, α-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 α- and β-TPB on Raman scattering, IR, and UV−vis optical properties are discussed.
  05/2010;
• Article: Polarized absorption, spontaneous and stimulated blue light emission of J-type tetraphenylbutadiene monocrystals.

  Silvia Tavazzi, Leonardo Silvestri, Luciano Miozzo, Antonio Papagni, Peter Spearman, Sandra Ianelli, Alberto Girlando, Andrea Camposeo, Marco Polo, Dario Pisignano
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  ABSTRACT: Blue amplified spontaneous emission at room temperature is demonstrated from the exposed face of the strongly emitting organic semiconductor 1,1,4,4-tetraphenyl-1,3-butadiene in single crystal form. The symmetry of the crystal and calculation of lattice sums indicate the J-type organization of the molecular transition moments. The minimum in the lowest exciton dispersion branch, from which emission takes place, is found at the edge of the Brillouin zone leading to a dominant vibronic emission since the zero-phonon line is forbidden. The observed gain narrowed line is attributed to the vibronic replica which becomes amplified with increased pumping. The reported emission is along the normal to the exposed crystal face, important for the development of vertical cavity geometry lasers based on organic single crystals. The threshold excitation fluence of 400 microJ cm(-2) is comparable to other organic crystalline systems, even if the amplification path is much reduced as a consequence of the vertical geometry. Considering these relevant aspects, the optical characterization of this material is provided. The polarized absorption spectra are reported and the properties of the lowest-energy excitonic state investigated. Calculation of the electronic transitions for the isolated molecule, lattice sums for the transition at lowest energy, and the symmetry of the crystal allow attributing the largest face of the samples and the observed optical bands in the spectra. Polarized time-resolved spectra are also reported allowing to identify the intrinsic excitonic emission.
  ChemPhysChem 02/2010; 11(2):429-34. · 3.41 Impact Factor