Upper-rim calixarene phosphines consisting of multiple lower-rim OH functional groups: synthesis and characterisation

The synthetic approaches to mono-isopropoxytrihydroxycalix[4]arenes bearing two or three diphenylphosphino groups at the upper macrocycle rim were elaborated. Due to reactive hydroxyl groups at the lower rim capable of binding with silica gel surface, the calixarenes, especially the enantiomerically pure inherently chiral diphosphinocalixarene, are promissing ligands for creation of hybride organic–inorganic metallocomplexing catalysts of organic (asymmetric) reactions.     

Infrared Spectra of the Free Base of Phthalocyanine and Its Deuterated Derivatives and their Interpretation

Journal of Applied Spectroscopy - The IR spectra of the free base of phthalocyanine and three of its deuterium derivatives were studied experimentally and theoretically. A detailed interpretation...     

Influence of Temperature on the Fluorescence Duration and Electronic Spectra of Metal-Free Tetrapyrroles in an Organic Polymer

Journal of Applied Spectroscopy - Spectral and luminescent characteristics and the duration of fluorescence were measured for a series of metal-free tetrapyrroles in polyvinylbutyral solid films at...     

Spectral and luminescent properties of triareno-substituted tetraazachlorins

Spectral and luminescent properties of recently synthesized compounds of a class of hydroporphyrazines, triarenotetraazachlorins, in polyvinylbutyral films have been studied. Fluorescence lifetimes have been measured in film and in solution. Fluorescence quantum yields have been estimated. It is found that annelation of aromatic rings to the pyrrole rings of the tetraazachlorin macrocycle enhances fluorescence. Quantum-chemical optimization of the geometrical structures of the free-base 1,2-trinaphthotetraazachlorins has been carried out using the AM1 method. The two isomers were shown to be highly non-planar. Spectral hole burning in absorption bands of both this compound and free-base 2,3-trinaphthotetraazachlorin in polyvinylbutyral films at 5 K in the wavelength region of titanium-sapphire laser radiation is possible and is ascribed to NH-photoisomerization. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 376–386, May–June, 2009.     

π-Electron ring currents and magnetic properties of porphyrin molecules in the MO LCAO SCF method

The coupled variant of double-parameter perturbation theory in the MO LCAO SCF method in the London approximation has been used for the calculation of π-electron current distributions in the molecules of porphin and its derivatives. The chemical shifts of¹H-NMR have been computed on the basis of calculations of ring currents and charge distributions. It is shown that π-electron ring currents are responsible for the dominant contribution to the shielding of protons. The theoretical and experimental values of proton chemical shifts are in a good agreement. Chemical shifts of the¹³C and¹⁵N nuclei have also been estimated. Two aromaticity scales are proposed for the compounds under study based on the calculations of the π-electron contribution to the diamagnetic susceptibility and of π-electron currents, respectively.     

Reactivity of gas barrier membranes filled with reactive particulates

Gas barrier plastic films and structures capable of removing a permeating solute via irreversible chemical reactions in the polymer matrix are investigated in applications of active packaging for controlling contained environments. To significantly reduce permeation rates through such active barriers, high barrier reactivity is required. When the reactive species take the form of fine particulates sparingly dispersed in the matrix, the reactivity of a composite membrane is affected by a lower frequency of collisions of dissolved gas molecules with the distributed reactive particles. The mean size of the particles and their volume fraction in the matrix are identified as the critical factors affecting the overall reactivity of uniformly filled composite barriers. A two-scale coarse-grained model of reaction-diffusion in a matrix is developed by introducing a unit cell approach to estimate the reaction rate upon collision with the particles and by choosing the unit length of diffusive molecular displacement equal to the mean diameter of the reactive particles to describe diffusion across the barrier and statistics of molecule-particle collisions. The corresponding method for evaluating the barrier reactivity is described. The effects of the system parameters on the effective gas transport rates across the reactive composite barriers including polymer nanocomposite barriers with reactive additives are quantified.     

Phenyl substituted Mg porphyrazines: The effect of annulation of a chalcogen-containing heterocycle on the spectral-luminescent properties

We have performed complex experimental and theoretical investigations of the spectral-luminescent properties and electronic structure of new phthalocyanine analogs, Mg octaphenylporphyrazine and its derivatives with an annulated thiadiazole or selenadiazole ring instead of two phenyl groups. Fluorescence characteristics have been determined at 293 and 77 K: emission, excitation, and fluorescence polarization spectra; fluorescence quantum yield ?? _F , and lifetime ?? _F . Annulation of a five-membered chalcogen-containing heterocycle leads to splitting of the long-wavelength absorption band Q(0-0) and to the bathochromic shift of its longest wavelength component Q _x (0-0), which increase upon passage from S to Se. At the same time, the fluorescence quantum yield ?? _F and lifetime ?? _F decrease, which is related to the intramolecular heavy-atom effect. The geometric structure of the ground state of the Mg porphyrazine molecules has been determined based on the density functional theory (DFT), and excited electronic states have been calculated with modified parametrization of the INDO/S method, INDO/Sm. Semiquantitatively, the calculated level positions of the lowest Q states and spectral shifts of Mg octaphenylporphyrazine and S-derivative agree with experimental data. For the range of the Soret band, calculated transition energies and their intensity distributions substantially depend on the dihedral angle ?? between a phenyl ring and porphyrazine macrocycle. We show that, based on calculations at the angle ?? = 60°, bands in the observed absorption spectra can be assigned with an accuracy of ??2000 cm^?1.     

Investigation of the octaethylporphin cationic forms in a silicate gel matrix by methods of low-temperature site selective spectroscopy

The spectral-luminescent properties of an octaethylporphin-doped inorganic xerogel prepared from tetraethoxysilane by the sol-gel method have been investigated. With the help of selective excitation and selective monitoring of fluorescence, it has been established that the octaethylporphin molecules, on their embedment into the gel matrix, form two cationic forms, dicationic and monocationic; the longest wavelength absorption band of the latter is shifted to the red. The significant influence of the gel matrix on the energy of the excited electronic Q states (S₁ and S₂) is shown. By the fluorescence line narrowing method at 4.2 K, fine-structure fluorescence and fluorescence excitation spectra of both forms have been obtained; the frequencies of the normal modes in the S₀ and S₁ states have been determined. The data on vibrational frequencies are interpreted on the basis of their juxtaposition with those from the fluorescence line narrowing spectrum of octaethylporphin and resonance Raman spectra of its complexes with copper and nickel. Cases of the appearance of out-of-plane vibrations in the fluorescence spectra have been revealed; their activation is explained by the nonplanarity of the porphyrin macrocycle for the cationic forms.     

X-ray diffraction structure analysis of MCM-48 mesoporous silica

The structure of MCM-48 mesoporous silicate materials has been fully characterized from X-ray diffraction data by applying recently developed methods of mesostructure analysis and full-profile refinement. The pore wall thickness of both as-made and calcined MCM-48 was determined with high precision to be 8.0(1) Angstrom. No regular variations of the wall thickness were detected, but its density was found to be ca. 10% higher in the low-curvature regions. The surfactant density in the pores was assessed around 0.6-0.7 g/cm(3) and was found to have a distinct minimum in the pore center similar to that detected previously in MCM-41. A new extended model function of the density distribution in MCM-48 is proposed on the basis of the structural features that were revealed.