TY  - JOUR
A1  - Shainyan, Bagrat A.
A1  - Suslova, Elena N.
A1  - Kleinpeter, Erich
T1  - Conformational analysis of 4,4-dimethyl-1-(trifluoromethylsulfonyl)-1,4-azasilinane and 2,2,6,6-tetramethyl-4-(trifluoromethylsulfonyl)-1,4,2,6-oxazadisilinane
JF  - Journal of physical organic chemistry
N2  - 4,4-Dimethyl-1-(trifluoromethylsulfonyl)-1,4-azasilinane 1 and 2,2,6,6-tetramethyl-4-(trifluoromethylsulfonyl)-1,4,2,6-oxazadisilinane 2 were studied by variable temperature dynamic 1H, 13C, 19F NMR spectroscopy and theoretical calculations at the DFT (density functional theory) and MP2 (Moller-Plesset 2) levels of theory. Both kinetic (barriers to ring inversion) and thermodynamic data (frozen conformational equilibria) could be obtained for the two compounds. The computations revealed two minima on the potential energy surface for molecules 1 and 2 corresponding to the rotamers with the CF3SO2 group directed inward and outward the ring, the latter being 0.20.4 kcal/mol (for 1) and 1.1 kcal/mol (for 2) more stable than the former. The vibrational calculations at the DFT and MP2 levels of theory give the values of the free energy difference Delta G degrees for the 'inward' reversible arrow 'outward' equilibrium consistent with those determined from the experimentally measured ratio of the rotamers. The structure of crystalline compound 2 was ascertained by X-ray diffraction analysis.
KW  - conformational analysis
KW  - dynamic NMR
KW  - quantum chemical calculations
KW  - 2
KW  - 6-disilamorpholines
KW  - 4-silapiperidines
Y1  - 2012
U6  - https://doi.org/10.1002/poc.1882
SN  - 0894-3230
VL  - 25
IS  - 1
SP  - 83
EP  - 90
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Shainyan, Bagrat A.
A1  - Kirpichenko, Svetlana V.
A1  - Kleinpeter, Erich
T1  - Synthesis and conformational properties of 1,3-dimethyl-3-phenyl-1,3-azasilinane low temperature dynamic NMR and computational study
JF  - Arkivoc : free online journal of organic chemistry
N2  - 1,3-Dimethyl-3-phenyl-1,3-azasilinane was synthesized and its conformational behavior was studied by the low temperature NMR spectroscopy and quantum chemical calculations. The compound was shown to exist as an equilibrium mixture of the PhaxMeeq and PheqMeax chair conformers with the N-methyl substituent in equatorial position. The barrier to ring inversion was also determined.
KW  - 1,3-Dimethyl-3-phenyl-1,3-azasilinane
KW  - conformational analysis
KW  - low temperature NMR spectroscopy
KW  - quantum chemical calculations
Y1  - 2012
SN  - 1551-7004
IS  - 24
SP  - 175
EP  - 185
PB  - ARKAT
CY  - Gainesville
ER  - 
TY  - JOUR
A1  - Scharsich, Christina
A1  - Lohwasser, Ruth H.
A1  - Sommer, Michael
A1  - Asawapirom, Udom
A1  - Scherf, Ullrich
A1  - Thelakkat, Mukundan
A1  - Neher, Dieter
A1  - Koehler, Anna
T1  - Control of aggregate formation in poly(3-hexylthiophene) by solvent, molecular weight, and synthetic method
JF  - Journal of polymer science : B, Polymer physics
N2  - Aggregate formation in poly(3-hexylthiophene) depends on molecular weight, solvent, and synthetic method. The interplay of these parameters thus largely controls device performance. In order to obtain a quantitative understanding on how these factors control the resulting electronic properties of P3HT, we measured absorption in solution and in thin films as well as the resulting field effect mobility in transistors. By a detailed analysis of the absorption spectra, we deduce the fraction of aggregates formed, the excitonic coupling within the aggregates, and the conjugation length within the aggregates, all as a function of solvent quality for molecular weights from 5 to 19 kDa. From this, we infer in which structure the aggregated chains pack. Although the 5 kDa samples form straight chains, the 11 and 19 kDa chains are kinked or folded, with conjugation lengths that increase as the solvent quality reduces. There is a maximum fraction of aggregated chains (about 55 +/- 5%) that can be obtained, even for poor solvent quality. We show that inducing aggregation in solution leads to control of aggregate properties in thin films. As expected, the field-effect mobility correlates with the propensity to aggregation. Correspondingly, we find that a well-defined synthetic approach, tailored to give a narrow molecular weight distribution, is needed to obtain high field effect mobilities of up to 0.01 cm2/Vs for low molecular weight samples (=11 kDa), while the influence of synthetic method is negligible for samples of higher molecular weight, if low molecular weight fractions are removed by extraction.
KW  - conformational analysis
KW  - conjugated polymers
KW  - crystallization
KW  - films
KW  - interaction parameter
KW  - molecular weight distribution
KW  - molar mass distribution
KW  - nucleation
KW  - photophysics
KW  - structure
KW  - UV-vis spectroscopy
Y1  - 2012
U6  - https://doi.org/10.1002/polb.23022
SN  - 0887-6266
VL  - 50
IS  - 6
SP  - 442
EP  - 453
PB  - Wiley-Blackwell
CY  - Hoboken
ER  -