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A series of donor-acceptor p-nitro-p'-alkoxy (OR) substituted (E,E,E)-1,6-diphenyl-1,3,5-hexatrienes were prepared and their properties and crystal structures investigated. The flouresence spectra of these crystals were red-shifted relative to those for the solutions in low polar solvents, which can be attributed to the planarization of molecules in the solid state and to the strong intermolecular interactions in crystals.

The CCSD(T) level interaction energies of CH/pi complexes at the basis set limit are estimated. The weak directionality has indicated that the hydrogen atom of the interacting C-H bond is not essential for the attraction and that the typical CH/pi interaction does not play a key role in determining the molecular orientation in molecular assemblies.

The ARS-E model was used for calculating the intermolecular interaction energy of hexafluorobenzene-benzene. The largest and most negative energy of -5.38 kcal/mol was observed in the slipped-parallel complex.

The interaction energies of the alkaline-earth-metal dication/benzene complexes were calculated at the MP2 level using the 6-311G-basis set. The calculations of benzene under an electric field show that the electric field produced by the diction is a cause of the C-C bond elongation in the alkaline-earth-metal dication/benzene complexes.

Calculation of intermolecular interaction energies of 14 orientation CHF3 dimers is done with electron correlation correction by the MP2 method. Electron correlation correction increases the attraction considerably, which indicates that the dispersion interaction is important for the attraction.

High-level ab initio calculations have been used to investigate the torsional potentials of methoxy and hydroxyl groups of omichron-hydroxyanisole. It was established that the intramolecular bond significantly stabilizes the energy minimum structure.

Estimation of the intermolecular interaction energies has been carried out by means of ab initio calculations of C (sub)2 H (sub)4 - CH (sub)4 and C (sub)2 H (sub)6 - CH (sub)4 dimer orientations. The role of the electrostatic, dispersion and charge transfer interactions between aliphatic C-H bond and pi-system has been discussed.

Two medium-size basis sets, aug(d,p)-6-311G** and aug(df,pd)-6-311G**, are developed to analyze the dispersion interactions of hydrocarbon molecules. Intermolecular interaction energies of methane, ethane, propane, ethylene, acetylene and benzene dimers calculated with the basis sets are compared with those from the Sadlej's basis set and Dunning's correlation-consistent basis sets. Results show that the aug(d,p)-6-311G** set is more effective than Sadlej's basis set in evaluating dispersion energy. The aug(df,pd)-6-311G** basis set is also smaller than Dunning's basis sets.

Ab initio methods using basis sets of up to 6-311G(2d) quality, with MP2 level electron correlation energy correction were used to examine the intermolecular interaction potential of the corannulene dimer in a parallel (D5h) orientation. Results indicate that the dispersion interaction is the dominant principle in the interaction of the corannulene dimer. Findings also suggest that the intermolecular interaction potential obtained from the corannulene dimer will outperform atom-atom potentials for molecular dynamics studies of the bulk properties of fullerenes.

A series of ring-fluorinated (E,E,E)-1,6-diphenyl-1,3,5-hexatrienes (DPHs) are synthesized and their solid-state absorption, fluorescence properties and the crystal structures are examined. The difference in the fluorescence origin is attributed to the difference in the strength of orbital-orbital interaction between molecular [pi]-planes in the ground and excited states in crystals.

The intermolecular interaction between an aliphatic C-H bond and a pi-electron system (C-H/pi interaction) is characterized on the basis of infrared spectroscopy and high level ab initio calculations. The [S.sub.1]/[S.sub.0] electronic transition of the aromatic moiety is observed, indicating low-frequency shifts upon cluster formation, and these results have supported the dominance of the dispersion interaction over the electrostatic and charge-transfer terms in the aliphatic C-H/pi interaction.

The accurate CH/pi interaction energy of the benzene-methane model system was experimentally and theoretically determined. The mass analyzed threshold ionization (MATI) technique was applied to benzene-methane cluster and the calculated binding energy after the vibrational zero-point energy correction was similar to the experimental value.

Intermolecular interaction energies of n-butane, n-pentane, and n-hexane dimers were calculated at the MP2 level with large basis set including multiple polarization functions. A comparison of the calculated interaction energies of five orientations of dimers for each n-alkane molecule showed that the interaction between the two n-alkane chains has strong anisotropy.

A molecular interaction between the fluorine atom and r -system of the hexafluorobenzene is examined. It is concluded that there is a very weak repulsive interaction between them.

The energy profiles for the internal bond rotation of substitutes methyl radicals, X-CH2 (X= BH2, CH3, NH2, and OH) are examined with B3LYP/6-31G(d) calculations. The computed rotational energy profiles, as well as the calculated values for the geometrical parameters, the vibrational frequencies, the ionization potential, are found to be reasonable in agreement with previously reported experimental and theoretical results.

The interaction energies of the cation/pi complexes were calculated at the MP2/6-311G level. The calculated potential suggests that the major source of the attraction in the cation/pi interaction is long-range interactions such as induction and electrostatic.

The CH/π contact structures of the fucose--phenol and fucose--indole complexes and the stabilization energies by formation of the complexes (Eform) were studied by ab initio molecular orbital calculations. The three types of interactions (CH/π and OH/π interactions and OH/O hydrogen bonds) were compared and evaluated in a single molecular system and at the same level of theory. The Eform calculated for the most stable CH/π contact structure of the fucose--phenol complex at the CCSD(T) level (-4.9 kcal/mol) is close to that for the most stable CH/π contact structure of the fucose--benzene complex (-4.5 kcal/mol). On the other hand the most stable CH/π contact structure of the fucose--indole complex has substantially larger Eform (-6.5 kcal/mol). The dispersion interaction is the major source of the attraction in the CH/π contact structures of the fucose--phenol and fucose--indole complexes as in the case of the fucose--benzene complex. The electrostatic interactions in the CH/π contact structures are small (less than 1.5 kcal/mol). The nature of the interactions between the nonpolar surface of the carbohydrate and aromatic rings is completely different from that of the conventional hydrogen bonds where the electrostatic interaction is the major source of the attraction. The distributed multipole analysis and DFT-SATP analysis show that the dispersion interactions in the CH/π contact structure of fucose--indole complex are substantially larger than those in the CH/π contact structures of fucose--benzene and fucose--phenol complexes. The large dispersion interactions are responsible for the large Eform for the fucose--indole complex. [ABSTRACT FROM AUTHOR]

Geometries of benzene complexes with C6F5X, C6H5X, and CF3X (X is I, Br, Cl, and F) were optimized, and their interaction energies were evaluated. The CCSD(T) interaction energies at the basis set limit (Eint) of C6F5X (X is I, Br, Cl, and F) with benzene were -3.24, -2.88, -2.31, and -0.92 kcal mol(-1). Eint of C6H5X (X is I, Br, and Cl) with benzene were -2.31, -1.97, and -1.48 kcal mol(-1). The fluorination of halobenzenes slightly enhances the attraction. Eint of CF3X (X is I, Br, Cl, and F) with benzene (-3.11, -2.74, -2.22, and -0.71 kcal mol(-1)) were very close to Eint of corresponding C6F5X with benzene. In contrast to the halogen bond of iodine and bromine with pyridine (n-type halogen bond acceptor) where the main cause of the attraction is the electrostatic interactions, that of halogen bond with benzene (p-type acceptor) is dispersion interaction. In the halogen bonds with p-type acceptors (halogen-π interactions), the electrostatic interactions and induction interactions are small. The overall orbital-orbital interactions are repulsive. The directionality of halogen bonds with p-type acceptors is very weak, owing to the weak electrostatic interactions, in contrast to the strong directionality of the halogen bonds with n-type acceptors and hydrogen bonds.

The diffusive properties of an imidazolium room-temperature ionic liquid (RTIL), 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide (DMPImTFSA), are studied from the ionic conductivity and the ion diffusion coefficients measured by pulsed field gradient spin echo NMR. The temperature-dependent (1)H, (19)F, and (13)C NMR spin-lattice relaxation time T(1) values were observed, and the (1)H T(1) for DMPIm showed T(1) minima for various protons. According to the Bloemberger-Purcell-Pound (BPP) equation, the correlation time tau(c) values were directly calculated from (1)H NMR. By using the (1)H tau(c) values, an evaluation of the (13)C T(1) was attempted for the carbons having protons. The tau(c) estimated for molecular motions of DMPIm changes from 1.3 ns at 253 K to 72 ps at 353 K. The Stokes-Einstein-Debye (SED) model suggests that the tau(c) is too short for the overall molecular reorientation near room temperature. Consequently, the possibility of small-angle molecular rotation is proposed and tentative flip angles are calculated by using the translational diffusion coefficient, the bulk viscosity measured in this study, and the tau(c) obtained from (1)H T(1) data in the temperature range between 283 and 353 K. The flip amplitude increases with the temperature. DMPIm has isotropic reorientational motions with temperature-dependent amplitude, in addition to fast intramolecular motions such as methylene segmental motions, methyl rotational motion, and conformational exchange of the imidazolium ring. The existence of fast motions of TFSA is also shown. The translational diffusion of the ions is the slowest dynamic process in the present RTIL. Ab initio molecular orbital calculations are performed to understand the geometries of stable complexes of DMPIm(+) and TFSA(-), and the formation energies from the isolated ions are evaluated. The computed results are important for interpreting the (1)H T(1) behaviors observed for the imidazolium ring protons.

The accurate interaction energies of the CH/pi interaction in the benzene-X clusters (X = ethylene and acetylene) were experimentally and theoretically determined. Two-color multiphoton ionization spectroscopy was applied, and the binding energies in the neutral ground state of the clusters were evaluated from the dissociation threshold measurements of the cluster cations. The experimental binding energies of the clusters (D0) were 1.4+/-0.2 and 2.7+/-0.2 kcal/mol, respectively. Estimated CCSD(T) interaction energies for the clusters at the basis set limit (De) were 2.2 and 2.8 kcal/mol, respectively. Calculated D0 values (1.7 and 2.4 kcal/mol, respectively) are close to the experimental values. Large electron correlation contributions (Ecorr=-3.6 and -2.8 kcal/mol, respectively) show that dispersion is the major source of the attraction in both clusters. The electrostatic interaction in the ethylene cluster is very small (-0.38 kcal/mol), as in the case of the benzene-methane cluster, whereas the electrostatic interaction in the acetylene cluster is large (-1.70 kcal/mol). The shifts of the S1-S0 transition also suggest that the ethylene cluster is a van der Waals-type cluster, but the acetylene cluster is a pi-hydrogen-bonded cluster. The nature of the CH/pi interaction of the "activated" alkyne C-H bond is significantly different from that of the "nonactivated" (or typical) alkane and alkene C-H bonds.