Monomeric Model Compounds Research Articles

Charge-transfer Complexes of Vinyl Polymers with Large Pendant π-electron Systems. I. Poly(N-vinylcarbazole) and Related Compounds

Abstract The absorption spectra and the thermodynamic constants (KCT, ΔH, and ΔS of formation) of the charge-transfer (CT) complexes of poly-N-vinylcarbazole (PVCz), the oligomers of N-vinylcarbazole (VCzOlig I and II, ‾DP=5 and 10 respectively), poly-N-carbazolylethylvinylether (PCzEVE), and the monomeric model compounds were examined in solution in order to clarify the characteristics of the complexes of polymeric donors with large pendant π-electron systems. The apparent spectra were resolved into two CT bands. The complexes of PVCz and VCzOlig II showed a lower frequency shift in the absorption maximum of the first CT band and an increase in the intensity ratio of the first to the second CT bands as compared with those of the monomeric complexes. This behavior, regarded as a kind of so-called polymer effect, seems to arise from some electronic interaction between neighboring carbazolyl groups in one polymer chain; it can be explained by variation both in the electron-donating character and in the distribution of the orientational isomers between the PVCz complexes and the others. A comparison of the observed values of KCT, ΔH, and ΔS among the donors suggested that a dominant factor in determining these values is the steric hindrance rather than the small difference in the electron-donating character in the case of the structurally related polymeric complexes. The steric hindrance is important in the complexes of PCzEVE and VCzOlig I, where the electronic interaction is hardly present.

Donor acceptor interactions in polymeric systems, 1. Synthesis and properties of polyamides having the carbazole group in the main chain

AbstractLow temperature polymerizations of 3,6‐diamino‐9‐ethylcarbazole (1b) with the diacyl dichlorides 2a—e were investigated. In all cases polyamides of high relative molecular mass ([η] ≈ 1·102 cm3 g−1). could be obtained. These polyamides are polymeric electron donors in which the donor units are arranged with regular intervals. Donor acceptor interactions between polyamides and 1,3,5‐trinitrobenzene were studied. In comparison with the monomeric model compound 9‐ethyl‐3,6‐bis(propionylamino) carbazole (1c) the polymer donor showed a higher stability constant. However, there is no regularity in the sequence of stability constants in respect to the number of methylene units separating two carbazole groups. There is a possibility that donor units in the polymer molecules might be located in such a way that each donor unit could cooperate to form a donor‐acceptor complex. No specific interactions between the carbazole groups could, however, be detected by fluorescence spectroscopy. The importance of solvent effects was expressed by the results of absorption and emission spectroscopy.

Carbon-13 nuclear magnetic resonance spectra of lignins

From the 13C-nmr spectra of a large number of dimeric and monomeric lignin model compounds the chemical shifts of the carbon atoms of the C 9-units in lignin with different substitution patterns were determined. The absorption peaks of the carbon-13 spectra of two lignins (beech and spruce) could be assigned by comparison (Table 3).

Studies on the Enzymatic Degradation of Lignin. The Action of Peroxidase and Laccase on Monomeric and Dimeric Model Compounds.

Studies on the Enzymatic Degradation of Lignin. The Action of Peroxidase and Laccase on Monomeric and Dimeric Model Compounds.

Photochromic polypeptides.

AbstractTwo photochromic polypeptides were synthesized by reaction of 1‐(4‐iodobutyl)‐3,3‐ dimethylindolindolino‐6′‐nitrobenzospiropyran with poly‐L‐tyrosine; their molar contents on photochromic units were 27.3 and 44.7%. The spectra of the photo‐induced merocyanines and their decoloration kinetics were compared with these of the monomeric model compound, obtained by reaction of the same N‐(4‐iodobutyl)‐indolinospiropyran derivative with N‐acetyltyrosine methyl ester. Different types of solvents have been examined, mainly dimethylformamide and pyridine, acetone and tetrahydrofuran, and methanol and ethylene glycol. The polypeptides showed a much less pronounced solvatochromism than their model; on the other hand, their absorption spectra presented two absorption maxima instead of one for the model. These differences in photochromic behavior were interpreted on the basis of the solvatation of the polymeric chain. Inverse photochromism was observed for polypeptide P2 as well as for the model in ethylene glycol solution; this effect is due to a higher merocyanine content at the thermal equilibrium spiropyran ⇌ merocyanine in high polar solvent.