A new class of chromophores has been fabricated that features both electron-releasing and electron-withdrawing groups fused via an intervening ethynyl moiety to the carbon framework of a (porphinato)metal complex. These species possess large molecular first-order hyperpolarizabilities (β). We report herein the synthesis, optical spectroscopy, and the hyper-Rayleigh scattering data used to determine the β values of two archetypal members of this new class of exceptional nonlinear chromophores:  [5-[[4‘-(dimethylamino)phenyl]ethynyl]-15-[(4‘‘-nitrophenyl)ethynyl]-10,20-diphenylporphinato]copper(II) and [5-[[4‘-(dimethylamino)phenyl]ethynyl]-15-[(4‘‘-nitrophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II). One of these compounds, [5-[[4‘-(dimethylamino)phenyl]ethynyl]-15-[(4‘‘-nitrophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), possesses β values near 5000 × 10-30 esu at incident irradiation wavelengths of both 830 and 1064 nm. These studies suggest that this chromophoric structural motif may find utility...

Push−Pull Arylethynyl Porphyrins: New Chromophores That Exhibit Large Molecular First-Order Hyperpolarizabilities

Crystal Structures, Phase Transitions and Energy Calculations of Poly(p-phenylene) Oligomers

A correct description of the electronic excitations in polyenes demands that electron correlation is accounted for correctly. Very large expansions are necessary including many‐electron configurations with at least one, two, three, and four electrons promoted from the Hartree–Fock ground state. The enormous size of such expansions had prohibited accurate computations of the spectra for polyenes with more than ten π electrons. We present a multireference double excitation configuration interaction method (MRD‐CI) which allows such computations for polyenes with up to 16 π electrons. We employ a Pariser–Parr–Pople (PPP) model Hamiltonian. For short polyenes with up to ten π electrons our calculations reproduce the excitation energies resulting from full‐CI calculations. We extend our calculations to study the low‐lying electronic excitations of the longer polyenes, in particular, the gap between the first optically forbidden and the first optically allowed excited singlet state. The size of this gap is shown to depend strongly on the degree of bond alternation and on the dielectric shielding of the Coulomb repulsion between the π electrons.

The low‐lying electronic excitations in long polyenes: A PPP‐MRD‐CI study

We present an atomic-resolution observation and analysis of graphene constrictions and ribbons with sub-nanometer width. Graphene membranes are studied by imaging side spherical aberration-corrected transmission electron microscopy at 80?kV. Holes are formed in the honeycomb-like structure due to radiation damage. As the holes grow and two holes approach each other, the hexagonal structure that lies between them narrows down. Transitions and deviations from the hexagonal structure in this graphene ribbon occur as its width shrinks below one nanometer. Some reconstructions, involving more pentagons and heptagons than hexagons, turn out to be surprisingly stable. Finally, single carbon atom chain bridges between graphene contacts are observed. The dynamics are observed in real time at atomic resolution with enough sensitivity to detect every carbon atom that remains stable for a sufficient amount of time. The carbon chains appear reproducibly and in various configurations from graphene bridges, between adsorbates, or at open edges and seem to represent one of the most stable configurations that a few atomic carbon system accommodates in the presence of continuous energy input from the electron beam.

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From graphene constrictions to single carbon chains

Two algorithms for many-body interaction energy decomposition within the Hartree−Fock approximation are presented. These two schemes, which are extensions of the two-body Kitaura−Morokuma (KM) analysis and the reduced variational space self-consistent-field (RVS SCF) method, decompose the interaction energy into electrostatic, exchange, polarization, and charge transfer components. The Hartree-Fock interaction energies for the optimum water dimer, trimer, and tetramer were analyzed in terms of two-, three-, and four-body terms of these individual components. Counterpoise calculations of the exchange and charge transfer components proposed by Tomasi were performed to estimate the basis set superposition errors. The results show that the three-body nonadditive terms of water trimer and tetramer are dominated by the polarization and charge transfer components at their optimized structures with various basis sets and that the four-body term of water tetramer is very small. The RVS SCF energy components, whose...

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1307&context=chem_pubs

Energy Decomposition Analyses for Many-Body Interaction and Applications to Water Complexes

We present Pariser–Parr–Pople (PPP) calculations on long polyene and polydiacetylene oligomers containing up to 32 carbon atoms. Working at both PPP restricted Hartree–Fock and PPP configuration interaction with single excitations levels, we study the excitation towards the 1 1B+u state. We report, as a function of chain length, the evolution of the transition energies and the modifications in geometry and atomic charges along the backbones. Comparison is made between the two series of oligomers. In the longer molecules, localization of the excitation is found, in agreement with the excitonic character of the transition to the 1 1B+u state.

Long polyene and polydiacetylene oligomers: Pariser–Parr–Pople investigation of the geometric and electronic structures in the first 1Bu excited state

Static polarizability and second hyperpolarizability have been calculated for a number of small moleculesCO2, OCS, CS2, C2H2, C2H6, C3H8, cyclo-C3H6, C3H4, C3H6, SiH4, Si2H6in the framework of the coupled-perturbed Hartree-Fock (CPHF) theory. The linear and nonlinear coefficients have been calculated with standard Gaussian basis sets and 3-21G bases moderately enlarged with diffuse functions. It is shown that the parallel component of the polarizability saturates rapidly, which suggests that a 3-21G basis containing s and p diffuse functions is sufficient to reproduce αzz. For the αxx and αyy components, a 3-21G basis with s, p, and d diffuse functions is required. In general, the concordance between α computed with this basis set and the experimental static polarizability is at least of the order of 80%. On the contrary, the computation of the second hyperpolarizability with the same basis set for CO2, CS2, and C2H2 gives values that are 30% too low, compared to the experimental value. Better results are observed for ethane, propane, and cyclopropane for which the error is lower than 50%. The better agreement observed for the saturated compounds can probably be explained by their saturated character.

Ab initio CPHF calculations of the static polarizability and second hyperpolarizability of small molecules: Comparisons between standard and moderately large basis sets augmented with diffuse functions

Using ab initio STO-3G calculations, we compute and analyze the equilibrium geometry and the electric polarizability of five series of polycumulenes H2—[—Ck—]x—H2, k = 2–6, and x = 1–3. The importance of structural relaxations depends on the parity of k, and the average polarizabilities, calculated with the finite-field method, are significantly influenced by these structural changes. The trends in polarizability are briefly discussed in terms of the optical gap and the dipole transition moment.

Finite hydrocarbon chains incorporating cumulenic structures: prediction by ab initio calculations of their equilibrium geometry and electric polarizability

Electronic structure and nonlinear optical properties of aromatic polymers and their derivatives

The equilibrium geometry, stabilization energy, and electric polarizability of formic acid, formamide, and the three possible cyclic hydrogen-bonded pairs are obtained by ab initio calculations using the STO-3G, 4-31G, and 6-31G** bases. These three properties are found to be very much dependent on the basis set extension. The polarizability of the dimers is found to be basically additive in contribution from the monomeric moieties.

M. Dory

Papers

Long polyene and polydiacetylene oligomers: Pariser–Parr–Pople investigation of the geometric and electronic structures in the first 1Bu excited state

Ab initio CPHF calculations of the static polarizability and second hyperpolarizability of small molecules: Comparisons between standard and moderately large basis sets augmented with diffuse functions

Finite hydrocarbon chains incorporating cumulenic structures: prediction by ab initio calculations of their equilibrium geometry and electric polarizability

Electronic structure and nonlinear optical properties of aromatic polymers and their derivatives

Equilbrium geometry and electrical polarizability of formic acid, formamide and their cyclic hydrogen‐bonded paris