J-Aggregates of Astaxanthin and Its Monoesters and Diesters

Moscow University Chemistry Bulletin - The conditions for the preparation of astaxanthin ester aggregates are optimized, and their physicochemical characteristics (size and absorption spectra) are...     

Factors affecting photoisomerization of 4-styrylpyridine

Photoisomerization of 4-styrylpyridine at different irradiation wavelengths (λ 365 and 254 nm) and in different solvents was studied by UV and ¹H NMR spectroscopy. A procedure for recording the UV spectra of 4-styrylpyridine dissolved in liquid crystalline films freely suspended within a frame. The results of quantum-chemical calculations of the geometry and UV spectra of 4-styrylpyridine isomers are presented.     

First mesogenic derivative of boron difluoride β-enaminoketonate

Boron difluoride complexes possessing liquid crystalline and luminescent properties were synthesized for the first time on the basis of non-mesogenic β-enaminoketones.     

Synthesis and photoisomerization of mesogenic 4-alkoxystyrylpyridines

Introduction of long-chain alkoxy substituents into molecules of styrylpyridines as potential ligands for photosensitive metal complexes endows them with liquid crystalline properties over a wide temperature range. trans-cis Photoisomerization of 4-alkoxystyrylpyridines in solution was revealed by NMR and electronic absorption spectroscopy, and the kinetics of transformations of their molecular forms after irradiation were estimated. Photoinduced trans→cis isomerization of 4-alkoxystyrylpyridines is characterized by a higher rate, and intramolecular cyclization of their cis isomers after irradiation is slower, as compared to unsubstituted analog.     

Liquid-Crystalline and Orientation Properties of Lanthanide Complexes with β-Enaminoketone

A series of liquid-crystalline lanthanide complexes with 1-(4-dodecyloxyphenyl)-3-octadecylamino-2-propene-1-one (HL), which is substituted β-enaminoketone, with the composition Ln(HL)₃(NO₃)₃ (Ln = La, Nd, Gd, Tb, Dy, Ho, and Er) is synthesized. For the most part of the synthesized complexes, the magnetic susceptibility anisotropy (Δχ_min) is shown to be one to two orders higher than Δχ of the “classical” organic liquid crystals.     

Specific features of spin-variable properties of [Fe(acen)pic<Subscript>2</Subscript>]BPh<Subscript>4</Subscript> · <Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O

The [Fe(acen)pic₂]BPh₄ · nH₂O compound has been synthesized and studied in the temperature interval of 5–300 K by the methods of EPR and magnetic susceptibility. The existence of ferromagnetic interactions between Fe(III) complexes in this compound has been revealed, in contrast to unhydrated [Fe(acen)pic₂]BPh₄. The reduction in the integrated intensity of the magnetic resonance signal as the temperature decreases below 80 K has been explained by the transition of high-spin ions to the low-spin state. It has been shown that the phase transition temperature in the presence of intermolecular (ferromagnetic) interactions is lower than that in the case of noninteracting centers.     

A study of the precipitation mechanism in GK transformer oil

The room-temperature IR spectra of fresh, used, and aged under model conditions GK trans-former oil, as well as of its residue, are recorded, interpreted, and compared. Analysis of the data obtained confirms the presence of small amounts of aromatic compounds in these samples and shows that the fraction of aromatic and oxidized compounds in transformer oil increases during exploitation. Based on this, a new precipitation mechanism in transformer oil is proposed.     

UV spectroscopy of GK transformer oil

A simple and efficient method is proposed for obtaining a thin layer of transformer oil in a standard cell for the recording of UV spectra. UV and visible absorption spectra of fresh, used, and aged (under model conditions) transformer oil of the GK type have been recorded, interpreted, and compared. The method is shown to be promising for the monitoring and qualitative analysis of the composition and content of aromatic compounds in transformer oils during the operation of power transformers.