n-Type 1D nanostructures are formed from the beta-sheet assembly of dipeptides bearing a 1,4,5,8-naphthalenetetracarboxylic acid diimide (NDI) side chain into either helical nanofibers or twisted nanoribbons. Amyloid-like 1-D helical nanofibers and twisted nanoribbons assemble in an aqueous solution depending on the placement of the NDI group. beta-Sheet-type hydrogen bonding and pi-pi association play important roles in directing the assembly process. A delicate balance between electrostatic repulsion and hydrophobic interactions is critical for self-assembly. Fluorescence lifetime and anisotropy experiments indicate that the nature of the intermolecular organization and packing within the nanostructures critically impacts intermolecular energy migration pi-electron delocalization.

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The lone pair-π interaction between H(2)O and C(6)F(6) was studied using matrix isolation infrared spectroscopy and quantum chemical calculations. Co-deposition of H(2)O with C(6)F(6) in a nitrogen matrix at 17 K followed by annealing to 30 K, results in the appearance of multiple new peaks in the infrared spectrum that are shifted from the H(2)O and C(6)F(6) parent absorptions. These peaks only appear when both the H(2)O and C(6)F(6) are present and have been assigned to distinct structures of a 1:1 H(2)O·C(6)F(6) complex. Similar experiments were performed with D(2)O and HDO and the corresponding infrared peaks for the structures of the D(2)O·C(6)F(6) and HDO·C(6)F(6) complexes have also been observed. Theoretical calculations were performed for the H(2)O·C(6)F(6) complex using the B3LYP, MP2, and CCSD(T) methods. Geometry optimizations at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ levels of theory located three structural minima, all of which involve the lone pair-π interaction between the H(2)O and the C(6)F(6) ring, but with different relative orientations of the H(2)O and C(6)F(6) subunits. BSSE corrected interaction energies were estimated at the CCSD(T)/aug-cc-pVTZ level and found to be between -11.2 and -12.3 kJ/mol for the three H(2)O·C(6)F(6) structures. Vibrational frequencies for the each of the structures were calculated at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ levels. The frequencies calculated with both methods support the assignments of the observed new peaks in the infrared spectra to the structures of the H(2)O·C(6)F(6) complex; however, the B3LYP calculated frequency shifts were found to be in better quantitative agreement with the experimentally observed frequency shifts.

Ab initio calculations have been used to investigate the interaction energies of dimers of dimethyl ether with benzene, hexafluorobenzene, and several monosubstituted benzenes. The potential energy curves were explored at the MP2/aug-cc-pVDZ level for two basic configurations of the dimers, one in which the oxygen atom of the dimethyl ether was pointed towards the aromatic ring and the other in which the oxygen atom was pointed away from the aromatic ring. Once the optimum intermolecular distances between the dimethyl and the aromatic ring had been determined for each of the dimers in both configurations at the MP2/aug-cc-pVDZ level, single point energy calculations were performed at the MP2/aug-cc-pVTZ level. A CCSD(T) correction term to the energy was determined and this was combined with the MP2/aug-cc-pVTZ energies to estimate the CCSD(T)/aug-cc-pVTZ interaction energies of the dimers. The estimated CCSD(T)/aug-cc-pVTZ interaction energies are predicted to be attractive for all of the dimers in both configurations and dispersion interactions are found to be a large component of the stabilization of the dimers. For the dimers with the dimethyl ether oxygen pointing towards the aromatic ring, the strengths of interaction energies are found to increase as the aromatic ring becomes more electron deficient, while for the dimers with the dimethyl ether oxygen pointing away from the aromatic ring, they increase as the aromatic ring becomes more electron rich. In both cases, the trends can be explained in terms of the electrostatic potentials of the dimethyl ether and the aromatic rings.

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