The piezoelectric properties of 2-methyl-4-nitroaniline crystals were explored qualitatively and quantitatively using an electrostatically embedded many-body (EE-MB) expansion scheme for the correlation energies of a system of monomers within the crystal. The results demonstrate that hydrogen bonding is an inherently piezoelectric interaction, deforming in response to the electrostatic environment. We obtain piezo-coefficients in excellent agreement with the experimental values. This approach reduces computational cost and reproduces the total resolution of the identity (RI)-Møller-Plesset second-order perturbation theory (RI-MP2) energy for the system to within 1.3 × 10(-5)%. Furthermore, the results suggest novel ways to self-assemble piezoelectric solids and suggest that accurate treatment of hydrogen bonds requires precise electrostatic evaluation. Considering the ubiquity of hydrogen bonds across chemistry, materials, and biology, a new electromechanical view of these interactions is required.

Organic piezoelectric materials are promising targets in applications such as energy harvesting or mechanical sensors and actuators. In a recent paper (Werling, K. A.; et al. J. Phys. Chem. Lett. 2013, 4, 1365-1370), we have shown that hydrogen bonding gives rise to a significant piezoelectric response. In this article, we aim to find organic hydrogen bonded systems with increased piezo-response by investigating different hydrogen bonding motifs and by tailoring the hydrogen bond strength via functionalization. The largest piezo-coefficient of 23 pm/V is found for the nitrobenzene-aniline dimer. We develop a simple, yet surprisingly accurate rationale to predict piezo-coefficients based on the zero-field compliance matrix and dipole derivatives. This rationale increases the speed of first-principles piezo-coefficient calculations by an order of magnitude. At the same time, it suggests how to understand and further increase the piezo-response. Our rationale also explains the remarkably large piezo-response of 150 pm/V and more for another class of systems, the "molecular springs" (Marvin, C.; et al. J. Phys. Chem. C 2013, 117, 16783-16790.).

Single molecule conductance measurements on alkanedithiols and alkoxydithiols (dithiolated oligoethers) were performed using the STM-controlled break junction method in order to ascertain how the oxygen heteroatoms in saturated linear chains impact the molecular conductance. The experimental results show that the difference in conductance increases with chain length, over the range studied. Comparisons with electronic structure calculations and previous work on alkanes indicate that the conductance of the oligoethers is lower than that of alkane chains with the same length. Electronic structure calculations allow the difference in the conductance of these two families of molecules to be traced to differences in the spatial distribution of the molecular orbitals that contribute most to the conductance. A pathway analysis of the electronic coupling through the chain is used to explain how the difference in conductance between the alkane and oligoether molecules depends on the chain length.

The infrared spectra of EDTA complexed with Ca 2+ and Mg 2+ contain, to date, unidentified vibrational bands. This study assigns the peaks in the linear and two-dimensional infrared spectra of EDTA, with and without either Ca 2+ or Mg 2+ ions. Two-dimensional infrared spectroscopy and DFT calculations reveal that, in both the presence and absence of ions, the carboxylate symmetric stretch and the terminal CH bending vibrations mix. We introduce a method to calculate participation coefficients that quantify the contribution of the carboxylate symmetric stretch, CH wag, CH twist, and CH scissor in the 1400−1550 cm −1 region. With the help of participation coefficients, we assign the 1400−1430 cm −1 region to the carboxylate symmetric stretch, which can mix with CH modes. We assign the 1000−1380 cm −1 region to CH twist modes, the 1380−1430 cm −1 region to wag modes, and the 1420−1650 cm −1 region to scissor modes. The difference in binding geometry between the carboxylate− Ca 2+ and carboxylate−Mg 2+ complex manifests as new diagonal and cross-peaks between the mixed modes in the two complexes. The small Mg 2+ ion binds EDTA tighter than the Ca 2+ ion, which causes a redshift of the COO symmetric stretches of the sagittal carboxylates. Energy decomposition analysis further characterizes the importance of electrostatics and deformation energy in the bound complexes.

We report a novel crystalline supramolecular polybenzobisimidazole (SP-PBBI) capable of providing a twodimensional polymer (2DSP-PBBI) by liquid-phase exfoliation. A regular arrangement of rigid rod-like polybenzobisimidazole (PBBI) chains is achieved by interchain hydrogen bonding. Titration of 2DSP-PBBI with cobalt chloride (CoCl 2 ) using UV-Vis spectroscopy demonstrates the presence of bidentate NO ligands on the PBBI backbone and NO-Co(II) complexation. Imaging analysis using atomic force microscopy (AFM) reveals the planar surface morphology of exfoliated 2DSP-PBBI sheets with lateral dimensions of <1 lm and thickness of <30 nm. The size of the polymer crystal growth is tuned by employing condensation/ precipitation polymerization under nonisothermal conditions.