Planarity ofparaHexaphenyl

Abstract

We present experimental and theoretical findings on the geometry of polycrystalline para hexaphenyl via Raman scattering. The planarity of the molecule is affected by hydrostatic pressure and temperature.Our studies indicate that the potential energy curve which governs the torsional motion between neighboring phenyl rings is "W" shaped. We determine the activation energy to promote the molecule from a nonplanar to a planar state to be 0.04 eV, in good agreement with our quantum chemical calculations. From the relative intensities of the 1280 cm 21 to the 1220 cm 21 Raman modes we show that high pressure planarizes the molecules, modifying the "W"-shaped potential energy curve to a "U"-shaped one.[S0031-9007(99)09073-0]

Tuning Intermolecular Interactions in Dioctyl-Substituted Polyfluorene via Hydrostatic Pressure

“…25 Such changes in oligophneyls have been attributed to planarization of the molecule. The repulsion between the ortho-hydrogen atoms leads to a torsion of neighboring phenyl rings with respect to the single bond connecting them.…”

“…25,26 The pressure dependent optical studies in PHP and other oligophenyls further reveal the individual contributions of the intermolecular and intramolecular interactions. 25 Optical studies in PFs under pressure allow tuning of the rich phase space and its impact on electron-phonon interactions. Our previous work on PF2/6 under pressure shows dramatic changes in the PL spectrum that mainly originates from defect and aggregate states.…”

Geometry-Dependent Electronic Properties of Highly Fluorescent Conjugated Molecules

“…The effective conjugation depends on the degree of overlap of the p-electron wave functions [12]. Therefore, the observed shifts under pressure can be explained by a higher degree of conjugation due to the stronger overlap of p electrons, i.e., a higher degree of planarity [4,12] or shorter inter-ring bonds [13].…”

“…However, in the solid state, the electronic properties depend on threedimensional interactions [2,3]. These interactions lead to completely new transitions due to collective states such as aggregates [2] or to shifts of the energy levels of single molecules due to changes in the molecular geometry [4].The focus of this study is the influence of molecular geometry and intermolecular interaction on the electronic properties of films of methylated laddertype poly(paraphenylene) (m-LPPP) [5]-a material of very low defect content [6], used for blue and white light emitting devices [7]. The small inhomogeneous broadening in m-LPPP makes the electronic spectra easily detectable fingerprints for the involved states.…”

“…However, in the solid state, the electronic properties depend on threedimensional interactions [2,3]. These interactions lead to completely new transitions due to collective states such as aggregates [2] or to shifts of the energy levels of single molecules due to changes in the molecular geometry [4].…”