No abstract

Carbon-13 longitudinal relaxation times and NOE values were measured as a function of temperature at three magnetic fields for poly(N-vinylcarbazole) (PNVC) in five solvents, covering viscosities differing by a factor of 5. The relaxation data of the backbone carbons were interpreted in terms of chain local motions by using the bimodal time-correlation function of the Dejean−Laupretre−Monnerie (DLM) model. The molecular correlation times obtained from the DLM model follow a linear relationship with solvent viscosity with unit slope, indicating that the hydrodynamic behavior of PNVC can be described by Kramers' theory. Several time-correlation functions describing internal motion failed to reproduce the experimental relaxation data of the protonated aromatic carbons of the carbazole side-group. It was concluded that the internal motion of the carbazole group is highly restricted due to strong steric effects from neighboring rings and the backbone chain. Finally, on the basis of our data some general conclusions were drawn regarding the influence of the backbone rearrangement of PNVC on its photophysical behavior.

NOESY experiments and molecular mechanics calculations have been used to examine the solution conformation of the synthetic polymer poly(N-vinylcarbazole) (PNVC). The diagonal and cross-peak volumes of theoretical NOESY spectra have been calculated for several mixing times by employing the complete relaxation matrix analysis (CORMA) introducing as structural models for the polymer chain conformation the triad stereochemical sequences (isotactic, heterotactic, and syndiotactic). Comparison between measured volumes and volumes calculated from the proposed structures allowed an assessment of the validity of the model structures. The data do not support a single conformational model, and only conformational averaging between different model structures can provide satisfactory agreement between theoretical and experimental parameters. On the basis of the conformational preference of the bulky carbazole groups of PNVC in the various stereochemical sequences, some useful conclusions were derived in relation to the photophysical behavior of this commercial polymer.

High‐level ab initio calculations were performed at the restricted Hartree–Fock (RHF) level of theory on carbazole and its N‐methyl and N‐ethyl derivatives. Single‐point gauge‐invariant atomic orbitals (SP GIAO) RHF NMR calculations on ab initio RHF optimized geometries were performed. The 6–31G* and 6–311++G** basis sets were used and some calculations were performed within a density functional theory using a recent B3PW91 hybrid functional. The theoretically predicted multinuclear magnetic resonance chemical shifts of carbazole and its N‐methyl and N‐ethyl derivatives in the gas phase are compared with experimental NMR data in CDCl3 solutions. A revised assignment of 13C NMR spectra of simple carbazoles is proposed. Copyright © 2000 John Wiley & Sons, Ltd.

High-level ab initio calculations were performed at the restricted Hartree-Fock (RHF) level of theory on carbazole and its N-methyl and N-ethyl derivatives. Single-point gauge-invariant atomic orbitals (SP GIAO) RHF NMR calculations on ab initio RHF optimized geometries were performed. The 6-31G* and 6-311 CC G** basis sets were used and some calculations were performed within a density functional theory using a recent B3PW91 hybrid functional. The theoretically predicted multinuclear magnetic resonance chemical shifts of carbazole and its N-methyl and N-ethyl derivatives in the gas phase are compared with experimental NMR data in CDCl 3 solutions. A revised assignment of 13 C NMR spectra of simple carbazoles is proposed.