Toward the Rational Design of Organic Solar Photovoltaics: Application of Molecular Structure Methods to Donor Polymers.

Conjugated polymers are promising candidates in the design of polymer solar cell materials with suitable electronic properties. Recent studies show that the use of different functional groups as side chain in thiophene-based polymers changes the electronic and conformation structures. Here we design new thiophene-based molecules by replacing the hydrogen attached to the backbone of P3MT with electron-donating and electron-withdrawing groups.

An extended E⊗e Jahn-Teller Hamiltonian for large-amplitude motion: Application to vibrational conical intersections in CHSH and CHOH.

An extended E⊗e Jahn-Teller Hamiltonian is presented for the case where the (slow) nuclear motion extends far from the symmetry point and may be described approximately as motion on a sphere. Rather than the traditional power series expansion in the displacement from the C symmetry point, an expansion in the spherical harmonics is employed. Application is made to the vibrational Jahn-Teller effect in CHXH, with X = S, O, where the equilibrium CXH angles are 83° and 72°, respectively.

Communication: conical intersections between vibrationally adiabatic surfaces in methanol.

A set of seven conical intersections (CI's) in methanol between vibrationally adiabatic surfaces is reported. The intersecting surfaces represent the energies of the two asymmetric CH stretch vibrations regarded as adiabatic functions of the torsion and COH bend angles. The ab initio data are well described by an extended Zwanziger and Grant (E ⊗ e) model [J.

Nanostructures and electronic properties of a high-efficiency electron-donating polymer.

The development of organic photovoltaic (OPV) solar cells has seeded a bright hope of achieving low-cost solar energy harvesting. Practical realization and successful commercialization require enhancing the efficiency of solar energy harvesting, which, in turn, relies on the core understanding of structure-property relationships in OPV materials. Here, we report the first large-scale density functional calculations of the nanoconformational and electronic properties of the thieno[3,4-b]thiophene-alt-benzodithiophene copolymer (PTB7), a high-efficiency OPV material.

A new approach toward transition state spectroscopy.

Chirped-Pulse millimetre-Wave (CPmmW) rotational spectroscopy provides a new class of information about photolysis transition state(s). Measured intensities in rotational spectra determine species-isomer-vibrational populations, provided that the rotational populations can be thermalized. The formation and detection of S(0) vinylidene is discussed in the limits of low and high initial rotational excitation.

Torsion-inversion tunneling patterns in the CH-stretch vibrationally excited states of the G12 family of molecules including methylamine.

Two torsion-inversion tunneling models (models I and II) are reported for the CH-stretch vibrationally excited states in the G12 family of molecules. The torsion and inversion tunneling parameters, h(2v) and h(3v), respectively, are combined with low-order coupling terms involving the CH-stretch vibrations. Model I is a group theoretical treatment starting from the symmetric rotor methyl CH-stretch vibrations; model II is an internal coordinate model including the local-local CH-stretch coupling.

Improved force field for molecular modeling of poly(3-hexylthiophene).

An ab initio-based improved force field is reported for poly(3-hexylthiophene) (P3HT) in the solid state, deriving torsional parameters and partial atomic charges from ab initio molecular structure calculations with explicit treatment of the hexyl side chains. The force field is validated by molecular dynamics (MD) simulations of solid P3HT with different molecular weights including calculation of structural parameters, mass density, melting temperature, glass transition temperature, and surface tension. At 300 K, the P3HT crystalline structure features planar backbones with non-interdigitated all-trans hexyl side chains twisted ~90° from the plane of the backbone.

Molecular spectroscopy and dynamics: a polyad-based perspective.

The efficiency and insight of global, polyad-based modeling in overtone spectroscopy and dynamics is demonstrated. Both vibration and vibration-rotation polyads are considered. The spectroscopic implications of polyad Hamiltonians derive from their ability to account for the detailed line positions and intensities of spectral features and their unique predictive power.

Novel patterns of torsion-inversion-rotation energy levels in the ν11 asymmetric CH-stretch spectrum of methylamine.

The high-resolution infrared spectrum of methylamine (CH3NH2) has been recorded using slit-jet direct absorption spectroscopy in the ν11 CH-stretch region (2965-3005 cm(-1)) with a resolution of 0.0025 cm(-1). The 621 lines assigned by ground state combination differences represent 27 substates with |K(')| ≤ 2 for the A, B, E1, and E2 symmetries.

IR and FTMW-IR spectroscopy and vibrational relaxation pathways in the CH stretch region of CH3OH and CH3OD.

Infrared spectra of jet-cooled CH(3)OD and CH(3)OH in the CH stretch region are observed by coherence-converted population transfer Fourier transform microwave-infrared (CCPT-FTMW-IR) spectroscopy (E torsional species only) and by slit-jet single resonance spectroscopy (both A and E torsional species, CH(3)OH only). Twagirayezu et al. reported the analysis of ν(3) symmetric CH stretch region (2750-2900 cm(-1); Twagirayezu et al.

Vibrational coupling pathways in methanol as revealed by coherence-converted population transfer Fourier transform microwave infrared double-resonance spectroscopy.

Coherence-converted population transfer infrared-microwave double-resonance spectroscopy is used to record the infrared spectra of jet-cooled CH(3)OH and CH(3)OD. Population transfer induced by a pulsed IR laser is detected by Fourier transform microwave spectroscopy background-free using a two-MW pulse sequence. The observed spectrum of CH(3)OH in the nu(3) symmetric CH stretch region contains 12 interacting vibrational bands, whereas in CH(3)OD, only one vibrational band is observed in the same interval (2750-2900 cm(-1)).

Torsion-vibration coupling in methanol: diabatic behavior in the CH overtone region.

Through a fit to methanol CH overtone data, a previously developed 4-dimensional torsion-vibration Hamiltonian is extended to high CH stretch excitation as well as to high torsional excitation. The strength of the torsion-vibration coupling is found to increase with CH stretch excitation. Systematic patterns of near degeneracy (3-, 4-, and 6-fold) are found in different regions of quantum number space.

Conformational dependence of intramolecular vibrational redistribution in methanol.

Previous state-selected spectra of methanol in the 5nu(1) OH stretch overtone region [O. V. Boyarkin, T.

Torsion-vibration coupling in methanol: the adiabatic approximation and intramolecular vibrational redistribution scaling.

The four-dimensional model Hamiltonian of Wang and Perry [J. Chem. Phys.

Vibrational overtone spectroscopy of jet-cooled methanol from 5000 to 14 000 cm(-1).

Spectra of jet-cooled methanol in the overtone and combination region from 5000 to 14 000 cm(-1) have been obtained by means of infrared laser-assisted photofragment spectroscopy. Many of the observed features are assigned to combination bands of the type nnu(1)+nu(6), nnu(1)+nu(8), and nnu(1)+nu(6)+nu(8) (n=1,2,3), where nu(1) is the OH stretch, nu(6) is the OH bend, and nu(8) is the CO stretch. These bands show sharp torsion-rotation structure with features as narrow as 0.