Molecular Structures and Vibrational Spectra of - and -Polyacetylene and Their Oligoenes Revisited Using Density Functional Theory Calculations.

Polyacetylene, the most representative synthetic conducting polymer, has attracted much attention because it exhibits high conductivity upon doping. In this paper, molecular structures, electronic excitation energies, and Raman and infrared spectra were calculated using density functional theory for - and -oligoenes with various chain lengths up to the number of C═C bonds () of 100 and - and -polyacetylenes under one-dimensional periodic boundary condition. The harmonic vibrational frequencies obtained at the B3LYP/6-311G(d,p) level were scaled by the scaling factors determined with respect to the anharmonic vibrational frequencies using the B2PLYP method, in which the coefficients of the functional were optimized for -oligoenes.

Picosecond time-resolved polarized infrared spectroscopic study of photoexcited states and their dynamics in oriented poly(p-phenylenevinylene).

The picosecond time-resolved polarized infrared absorption spectra of the photoexcited states of an oriented poly(p-phenylenevinylene) [-(C6H4CH=CH)n-, PPV] film have been recorded in the 3600-1050 cm(-1) region. The time-resolved photoinduced infrared absorptions due to an electronic transition in the wavenumber region of 3600-1700 cm(-1) and vibrational transitions in the region of 1700-1050 cm(-1) have fast and slow decay components under all polarization conditions of the pump and probe pulses with respect to the orientation of PPV. The picosecond time-resolved infrared absorption spectra are analyzed by reference to the photoinduced and doping-induced infrared difference spectra of PPV.

Fermi resonance in CO2: a combined electronic coupled-cluster and vibrational configuration-interaction prediction.

The authors present a first-principles prediction of the energies of the eight lowest-lying anharmonic vibrational states of CO(2), including the fundamental symmetric stretching mode and the first overtone of the fundamental bending mode, which undergo a strong coupling known as Fermi resonance. They employ coupled-cluster singles, doubles, and (perturbative) triples [CCSD(T) and CCSDT] in conjunction with a range of Gaussian basis sets (up to cc-pV5Z, aug-cc-pVQZ, and aug-cc-pCVTZ) to calculate the potential energy surfaces (PESs) of the molecule, with the errors arising from the finite basis-set sizes eliminated by extrapolation. The resulting vibrational many-body problem is solved by the vibrational self-consistent-field and vibrational configuration-interaction (VCI) methods with the PESs represented by a fourth-order Taylor expansion or by numerical values on a Gauss-Hermite quadrature grid.

Transfer of photoenergy in pi-conjugated polymers. Two types of photoluminescence that involve energy transfer along a polymer chain.

Two types of energy transfer in pi-conjugated polymers have been investigated using time-resolved photoluminescence (PL) techniques: type i, perpendicular-type energy transfer from the 2,3-di(p-tolyl)quinoxaline unit to the pi-conjugated main chain of poly[2,3-di(p-tolyl)quinoxaline-5,8-diyl], and type ii, parallel-type energy transfer from the oligo(pyridine-2,5-diyl) (O-Py) unit to the oligo(selenophene-2,5-diyl) (O-Se) unit in a block-type copolymer of O-Py and O-Se. Both types of energy transfer were very fast with a time constant shorter than approximately 0.1 ns; in particular, the type ii energy transfer took place with a time constant of approximately 5 ps.