Absorption Spectra of Radical Ions of Low Molecular Weight Poly(methyl-n-propylsilane)sChain Length Dependence

Charge carrier mobility in poly[methyl(phenyl)silylene] studied by time-resolved terahertz spectroscopy and molecular modelling

Time-resolved terahertz spectroscopy and combination of quantum chemistry modeling and molecular dynamics simulations were used for the determination of charge carrier mobility in poly[methyl(phenyl)silylene]. Using time-resolved THz spectroscopy we established the on-chain charge carrier drift mobility in PMPSi as 0.02 cm(2) V(-1) s(-1). This value is low due to the formation of polarons: the hole is self-trapped in a potential formed by local chain distortion and the transient THz conductivity spectra show signatures of its oscillations within this potential well. This view is supported by the agreement between experimental and calculated values of the on-chain charge carrier mobility.

Mechanism of Electron and Hole Localization in Poly(dimethylsilane) Radical Ions

The mechanism of excess electron and hole localizations in radical ions of poly(dimethylsilane) (PDMS) has been investigated by means of molecular dynamics (MD) and extended Hückel methods. Oligo(dimethylsilane) composed of 100 monomer units of dimethylsilane, CH3(Si(CH3)2)(n)CH3 (n = 100), were used as a model of PDMS. Both wings of the oligomer were capped by a methyl group. First, the geometry of PDMS with a regular all-trans form was fully optimized by MM2+ energy gradient method. Next, the MD calculation was carried out for PDMS at 300 K. The structure of PDMS was gradually deformed as a function of simulation time, especially the dihedral angle of Si-Si-Si-Si backbone that was randomized. At time zero when the structure has the regular all-trans form, both the excess electron and hole were completely delocalized on the Si backbone of PDMS. After thermal activation, the localization of the electron and hole was found. The mechanism of the localization was discussed on the basis of theoretical results.

Electrochemical Cyclization/Cycloreversion Reactions of Diarylethenes

[reaction: see text]. Electrochemical oxidation of diarylethene derivatives induced cyclization or cycloreversion reactions. The reaction mechanism was studied with CV, absorption spectra, and theoretical calculation.

Charge-Doped and Heteroatom-Substituted Polysilane, Poly(vinylenedisilanylene), and Poly(butadienylenedisilanylene): Electronic Structures and Band Gaps

The effects of charge-doping and boron and phosphorus substitution on the electronic structures and band gaps of polysilane, poly(vinylenedisilanylene), and poly(butadienylenedisilanylene) were theoretically investigated by using density functional theory and time-dependent density functional theory. Band gaps of polymers were estimated both by extrapolations from excitation energies of oligomers up to 30 units and by calculations with the periodic boundary condition. It was found that charge-doping in the polysilane decreases the band gap more significantly than B and P substitutions. However, Si-Si bonds are easily broken by charge-doping. In contrast, B and P substitutions exert little influence on the strength of Si-Si bonds. From natural bond orbital analysis, it was concluded that charge-doping and heteroatom substitution bring about a lowering of the band gap in sigma conjugated polysilanes because of strong electron-hole interactions. The introduction of longer pi conjugated moieties was found to reduce band gaps of sigma-pi conjugated chains. In contrast to the sigma conjugated polysilanes, bridged structures and a different distribution of polarons were found in cations of sigma-pi conjugated chains.

Mechanism of silylene extrusion reaction in cyclic polysilane via triplet energy surface: a direct MO dynamics study

Dynamics of photoreaction of permethylcycloheptasilane (Me2Si)7 on the triplet state surface, (Me2Si)7 (T1) →> (Me2Si)6 + Me2Si (T1), has been investigated by means of the direct MO dynamics method in order to elucidate mechanism of silylene extrusion from the Si-ring following the triplet energy transfer from a carbonyl compound. Full dimensional potential energy surface calculated at the PM3 method was employed in the dynamics calculation: the total energy and energy gradient on each atom were calculated at each time step during the reaction. The calculations showed that the seven-membered Si-ring is spontaneously changed to the six-membered ring without activation barrier on T1 surface. The photoreaction of (Me2Si)7 is significantly fast (reaction is completed within 1.0 ps), although heavy molecule (silylene radical) is dissociated. This is due to the fact that the T1 surface is strongly repulsive for the coordinate between the silylene and the Si-ring. The mechanism of the silylene extraction from the Si-ring was discussed on the basis of theoretical results.Key words: direct MO dynamics, polysilane, photoreaction, permethylcycloheptasilane, silylene.