To enable the design of efficient organic electroluminescence (OLED) devices with desirable charge carrier transport properties, the mobilities of hole and electron in a series of compounds were studied computationally based on the Marcus electron transfer theory. MO calculations were performed, using the DFT B3LYP/6-31G* method in the Gaussian 98 program suite, on the following compounds: biphenyl (Bp), 4,4′biphenyldiamine (BA), triphenylamine (TPA), tri-p-tolylamine (TTA), 4-biphenylphenyl-m-tolylamine (BPTA), 4,4′-bis(phenyl-m-tolylamino)biphenyl (TPD), naphthalene (Np), 1-naphthyldiphenylamine (NDPA), 1-biphenylnaphthylphenylamine (BNPA), and 4,4′-bis(1-naphthylphenylamino)biphenyl (NPB). The geometries of these compounds in their neutral, cationic, and anionic states were optimized. The optimized geometries were then used to calculate the ionization potential, electron affinity, and reorganization energies. For compounds containing a biphenyl moiety (Bp, BA, BPTA, TPD, BNPA, and NPB), the inter-ring distance and torsional angle followed the trend neutral g cationic g anionic, except NPB in which these two parameters in anionic state were larger than the corresponding parameters in the cationic state because of a small contribution from the biphenyl moiety to its LUMO. Also, the ionization potentials follow the order Bp > BPTA ≈ BNPA > BA > NPB ≈ TPD. The electron affinities were calculated to range from -1.54 to -0.05 eV for all compounds except NPB which has a positive electron affinity 0.24 eV due to the dominant contribution of two naphthyl groups to LUMO. For most compounds, the reorganization energy λ + for the hole transport is larger than λfor the electron transport except NPB and BA py (constrained nitrogen pyramidal geometry). These exceptions were rationalized by the special structures for their anionic states. According to the magnitudes of λ + , compounds can be divided into two groups: λ + g 0.28 eV (BA pl (constrained planar nitrogen geometry) ≈ Bp > TPD ≈ NPB) for compounds containing biphenyl group with or without two amino groups and λ + e 0.2 eV (TPA ≈ TTA Bp > BPTA) for compounds with a dominating biphenyl group in their LUMO, λe 0.32 eV (NDPA > BNPA > Np > NPB) for compounds with a dominating naphthyl group in their LUMO, and the other compounds (TPA and TTA). From these results, λ + is determined mainly by the moiety which contributes predominantly to its HOMO, whereas λis determined mainly by the moiety which contributes predominantly to its LUMO. Therefore, by controlling the major contributors to the HOMO and LUMO, and by incorporating substituents to fine-tune the energy levels of these frontier orbitals (HOMO and LUMO), a systematic design of materials for OLED with desirable charge carrier transport properties should be feasible.

The charge transport properties of mer-tris(8-hydroxyquinolinato)aluminum(III) (mer-Alq), which is the most widely used electron transport material in OLED, were investigated by quantum chemistry calculations within the framework of the charge hopping model and Marcus electron transfer theory. Internal reorganization energies of 0.276 and 0.242 eV were calculated by the DFT-B3LYP method employing a 6-31 G* basis set for the electrons lambdai(e) and holes lambdai(h), respectively. The relative distances and orientations of Alq molecules in amorphous film were simulated by those in the beta-phase. The intermolecular charge-transfer integrals, Hda(h) and Hda(e), along all 14 hopping pathways were then calculated by the Koopmans Theorem in conjunction with the Hartree-Fock method employing a 6-31 G* basis set as well as by the direct coupling method. The results showed that there were some Hda(e) that were 1 order of magnitude larger than any Hda(h), because hopping pathways with effective overlaps of LUMOs can occur and, thus, large Hda(e). On the other hand, effective overlap of HOMO was absent in all pathways, resulting in a relatively small Hda(h). This difference in the magnitudes of Hda(e) and Hda(h) would predict a 2 orders of magnitude difference in the electron-transfer rate constants and account for the observed 2 orders of magnitude difference in the mobilities of electrons and holes.

The C–H···O sp 3 hydrogen bond in trisialic acid lactones has been examined by using long‐range COSY (LRCOSY) and ab initio calculations. From an analysis of the LRCOSY spectra, 3J correlations of BH9ax/AH8 and CH9ax/BH8 confirmed the existence of hydrogen‐bond connections of x+1C9–x+1H9ax···xO8. The theoretical bond energy of the hydrogen bond was estimated to be 1.0 or 1.6 kcal/mol by using two models. The acid‐catalyzed cooperative lactonization of oligosialic acids can be understood in terms of the additional C–H···O sp 3 stabilization in the lactone product. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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