Structures and photochromic properties of fulgides based on naphtho[1,2-<Emphasis Type="Italic">b</Emphasis>]furan and benzo[<Emphasis Type="Italic">g</Emphasis>]indole

The novel heterocyclic fulgides, i.e. 3-isopropylidene-4-{1-[5-methoxy-1-(4-methoxy-phenyl)-2-methyl-1H-benzo[g]indol-3-yl]ethylidene}dihydrofuran-2,5-dione and 3-isopropylidene-4-[1-(1-benzyl-5-methoxy-2-methyl-1H-benzo[g]indol-3-yl)ethylidene]dihydrofuran-2,5-dione, were prepared and isolated as E-isomers. Photochromism, E-configuration, and high resistance to photocoloration—photobleaching of solutions of these fulgides as well as 3-isopropylidene-4-[1-(5-methoxy-2-methylnaphtho[1,2-b]furan-3-yl)ethylidene]dihydro-furan-2,5-dione and 3-isopropylidene-4-[1-(5-methoxy-2-methyl-1-phenyl-1H-benzo[g]indol-3-yl)ethylidene]dihydrofuran-2,5-dione synthesized previously were shown by X-ray diffraction analysis, ¹H NMR spectroscopy and electronic absorption spectroscopy. The novel fulgides show fluorescence and high thermal stability of photogenerated cyclic form. Repeated photo-coloration—photobleaching is accompanied by reversible photoinduced E—Z isomerization. Benzo[g]indolyl fulgides are characterized by the longer wavelength absorption of both original (E) and photoisomeric cyclic (C) forms as compared to naphthofuran fulgide.     

Numerical model of the aspiration system of an internal combustion engine

A physicomathematical model of flow in the aspiration system of an internal combustion engine operating in a “cold” regime, i.e., for a prescribed motion of the crankshaft, has been constructed. An ideal single-species gas is used. Results of a series of calculations for a time interval of five operation cycles are presented. Deceased. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 6, pp. 125–131, November–December, 1998.     

Benzoid-Quinoid Tautomerism of Schiff Bases and Their Structural Analogs: LII.* Schiff Bases Derived from 6-tert-Butyl-5-hydroxy- and 5-Hydroxy-6-iodo-2,3-tetra-methylenebenzo[b]furan-4-carbaldehydes

Two series of Schiff bases, 4-aryl(alkyl)iminomethyl-6-tert-butyl-5-hydroxy- and 4-aryl(alkyl)iminomethyl-5-hydroxy-6-iodo-2,3-tetramethylenebenzo[b]furans were synthesized. These compounds in solution give rise to tautomeric benzoid-quinoid equilibrium; the fraction of the quinoid form in the equilibrium mixture increases with rise in solvent polarity and in going from N-aryl to N-alkyl derivatives. The benzoid tautomer shows fluorescence with an anomalous Stokes shift. The absorption and luminescence spectral properties of the examined Schiff bases make them promising as signal fragments of chemosensors for metal cations.     

Novel asymmetric dihetarylethenes derived from N-isopropylindole and thiophene: synthesis and photochromic properties

Novel asymmetric dihetarylethenes, viz., 3-(1-isopropyl-5-methoxy-2-methyl-1H-indol-3-yl)-4-(3-thienyl)furan-2,5-dione and 1-alkyl/aryl-3-(1-isopropyl-5-methoxy-2-methyl-1H-indol-3-yl)-4-(3-thienyl)-1H-pyrrole-2,5-diones, were obtained. These dihetarylethenes exhibit photochromism in solutions. Replacement of the N-methyl group in the indole fragment by the N-isopropyl group imparts photochromic properties to the resulting furan-2,5-dione derivative. The open forms of (N-isopropylindol-3-yl)pyrrole-2,5-diones are characterized by lower quantum yields of fluorescence, and their cyclic forms are thermally more stable.     

Benzoid-quinoid tautomerism of schiff bases and their structural analogs: LIII. Schiff bases derived from 5-hydroxy- and 5-hydroxy-6-nitro-2,3-diphenyl-1-benzofuran-4-carbaldehydes

4-Aryl(alkyl)iminomethyl-5-hydroxy-and 4-aryl(alkyl)iminomethyl-5-hydroxy-6-nitro-2,3-diphenyl-1-benzofurans were synthesized and were shown to exist in solution as equilibrium mixtures of benzoid and quinoid tautomers. The fraction of the quinoid form increases with rise in the solvent polarity and in going from N-aryl to N-alkyl derivatives; introduction of an electron-acceptor substituent (nitro group) into the 6-position of the benzofuran system also favors formation of the quinoid tautomer. Complex formation of alkali and alkaline-earth metal cations with the 5-hydroxy-6-nitro-2,3-diphenyl-1-benzofuran-4-carbaldehyde imine having a benzo-15-crown-5 fragment on the nitrogen atom is accompanied by specific changes in the luminescence spectrum and in the state of tautomeric equilibrium, so that this system may be regarded as tautomeric fluorogenic chemosensor for metal cations.     

Low-temperature X-ray study of benzoid-quinoid tautomerism in crystals of 2-(N,N-diphenylhydrazinoethylidene)-3(2H)-benzo[b]thiophenone

An X-ray investigation of 2-(N,N-diphenylhydrazinoethylidene)-3(2H)-benzo[b]thiophenone was performed at room and low (–80 °C) temperatures. It was established that the structure of this compound in the crystalline state at R-20 °C is intermediate between the ketoenehydrazine and hydroxyhydrazone forms, while at –80 °C the molecular structure is completely transformed to the hydroxyhydrazone form. This confirms the dynamic nature of hydrogen atom disordering in the molecule at 20 °C.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 104–106, January, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-04355).     

Selecting gas dynamics channel parameters for electrical discharge fast flowrate lasers

Using lasers with powers over l kW has become common in industry. Compactness and high efficiency are important requirements to take into account when designing lasers. Fast flowrate CO₂ lasers with independent discharges have wide application in industry, whose radiators are quite large because of the low density of the working gas. When considering the compactness and efficiency of these lasers, one must not ignore questions concerning the optimal correspondence of the characteristics for the pumping device (PD) of the gas and for the closed gas dynamics channel (CGDC) of the laser radiator. The PD must ensure circulation of the gas at a rate determined by the assigned power of the laser for the smallest size of the radiator and for small noise and vibration levels. The configuration and dimensions of the CGDC, the means of arranging its elements, the characteristics of the gas flow in the pumping zone, and the power of the active medium all determine the gas resistance of the closed channel and the loss of power at pump, which is 5 to 25% of the total power required in lasers with powers up to 10 kW [1, 2]. One may find information on the application of various PD in fast flowrate lasers [3–9], but there is no data on the characteristics of closed CGDC, which are determined by the PD parameters. There is currently an absence of literature dealing with the selection of optimal parameters for the electrical discharge, the gas flow, and the configuration of the flow section of the CGDC. We will take a comprehensive approach to determine the parameters for the gas flow in the pumping zone and the gas characteristics for the contour elements and the pumping device.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 3–8, November–December, 1986.     

Tautomeric crown-containing chemosensors for alkali-earth metal cations

Crown-containing arylimines of 5-hydroxy- and 5-hydroxy-6-nitro-2,3-diphenylbenzo[b]furan-4-carbaldehydes were synthesized and their structure, spectral, luminescent, and complexing properties were studied by means of ¹H and ¹³C NMR, IR, UV, and mass-spectrometry. In solution, these compounds exist as equilibrium mixtures of benzenoid and quinoid tautomers. The relative concentration of the quinoid form increases in the order of solvents: toluene, acetonitrile, 2-propanol, chloroform. The presence in the benzo[b]furan moiety of a strong withdrawing 6-NO₂ group favors stabilization of the quinoid tautomer. This finding is in accord with the results of the DFT B3LYP/6-311++g(d,p) calculations. Complexation of 5-hydroxy-6-nitro-2,3-diphenyl-1-benzofuran-4-carbaldehyde crown-containing imines with alkali and alkali-earth metal ions shifts the tautomeric equilibrium to the quinoid forms and is accompanied by blue shifts of the emission spectra. The Schiff bases obtained represent a new type of fluorescent tautomeric chemosensor for Mg²⁺, Ca²⁺ (benzo-15-crown-5 derivative), and Ba²⁺ (benzo-18-crown-6 derivative) displaying diagnostic changes in both absorption and emission spectra.