Anton Gáplovský

Spectral Properties of Substituted Coumarins in Solution and Polymer Matrices

The absorption and fluorescence spectra of substituted coumarins (2-oxo-2H-chromenes) were investigated in solvents and in polymer matrices. The substitutions involved were: (1) by groups with varying electron donating ability such as CH3, OCH3 and N(CH3)2, mainly, but not exclusively, in positions 7 and (2), by either CHO or 4-PhNHCONHN=CH- in position 3. While the spectra of non-substituted coumarin-3-carbaldehyde has absorptions at approximately 305 and 350 nm, substitution at position 7 leads to remarkable changes in the shape of the absorption spectrum and shifts the absorption to a longer wavelength. Similarly, the replacement of the formyl group with a semicarbazide group substantially influences the shape of the absorption spectrum, and coumarins which have only N(CH3)2 in position 7 experience small changes. These changes are associated with the increasing intramolecular charge transfer (ICT) character and increasing conjugation length of the chromophoric system, respectively, in the studied molecules. The fluorescence is almost negligible for derivatives which have H in this position. With increasing electron donating ability, and the possibility of a positive mesomeric (+M) effect of the substituent in position 7 of the coumarin moiety, the fluorescence increases, and this increase is most intense when N(CH3)2 substitutes in this position, for both 3-substituted derivatives. Spectral measurements of the studied coumarins in polymer matrices revealed that the absorption and fluorescence maxima lay within the maxima for solvents, and that coumarins yield more intense fluorescence in polymer matrices than when they are in solution. The quantum yield of derivatives which have a dimethylamino group in position 7 in polymer matrices approaches 1, and the fluorescence lifetime is within the range of 0.5–4 ns. The high quantum yield of 7-dimethylamino derivatives qualifies them as laser dyes which have kF higher than knr in the given medium. This is caused by stiffening of the coumarin structure in polar polymer matrices, such as PMMA and PVC, due to higher micro-viscosity than in solution and intermolecular dipole-dipole interaction between chromophore (dopant) and matrix.

Ultrasound effects on photochemical reactions, Part 1: photochemical reactions of ketones with alkenes

Ultrasound considerably enhances and simplifies photochemical reaction of cyclohexanone with cyclohexene. The Paterno-Büchi reaction of acetone with ethyl vinyl ether is enhanced by ultrasound and yields a different ratio of cis/trans oxetanes under sonication by comparison with the silent reaction. Sonication appears to affect the first reaction by homogenization of excited intermediates and by quenching the excited triplet state at the second reaction.

Reaction of 3-formylchromones with aromatic amino carboxylic acids

Abstract 2-Alkoxy-3-(arylaminomethylene)chroman-4-ones and 3-(aryliminomethyl)chromones were prepared by acid catalyzed reaction of 3-formylchromones with aromatic amino carboxylic acids in alcoholic reaction media. The results of the kinetic study have confirmed that 3-(aryliminomethyl)chromones are formed from 2-alkoxy-3-(arylaminomethylene)chroman-4-ones. The dependence of the reaction rate on reactant structure, the reaction media and the concentration of catalyst has been studied. In contrast to the alcoholic media reaction, the same reaction in dry aprotic reaction media yielded only 2-hydroxy-3-(arylaminomethylene)chroman-4-ones. No 3-(aryliminomethyl)chromones were isolated in that case.

Synthesis and study of novel coumarin derivatives potentially utilizable as memory media.

Novel coumarin derivatives, 2-oxo-2H-chromenecarbaldehyde hydrazones were prepared by reaction of substituted 2-oxo-2H-chromenecarbaldehydes with N-aminoimides in ethanol in the presence of 4-toluenesulfonic acid as catalyst. The photochromic and thermochromic properties of the prepared compounds were investigated.

Isatin N-phenylsemicarbazone: effect of substituents and concentration on anion sensing selectivity and sensitivity

The effect of substituent and concentration on anion sensing selectivity and sensitivity of nine new easily synthesized isatin N-phenylsemicarbazone E-isomer sensors IIIa–XIa was investigated. The substantial difference between the association constants for IIIa–XIa interaction with strongly and weakly basic anions allows detection of F− or CH3COO− anions even at high weakly basic anion excess. Substitution in position 5- of the isatin ring and para-substitution on the phenyl ring in the phenylsemicarbazide chain influence sensor:anion complex stoichiometry and thus also sensor sensitivity. Detection limits of 3–4 × 10−7 mol dm−3 for F− and CH3COO− anions by sensors IVa and Va bearing electron-withdrawing substituents are among the lowest published detection limits for these anions in organic solvents. The high selectivity and sensitivity of sensor VIa allows confident F− detection at tolerated fluoride drinking-water level. The solution dilution leads to a dramatic change in sensor selectivity. Consequently, one E-isomer can be used to sense both strongly and weakly basic anions. On the other side, higher sensor solution concentrations increase the F− and CH3COO− anion detection range, similar to the additional Z-isomer utilization.

Electronic spectra of ferrocenyl chalcones

The electronic absorption spectra of two series of ferrocenyl chalcones (Fc-CH=CH-CO-Ar,1 andFc-CO-CH=CH-Ar,2) in methanol andn-hexane were recorded. Excellent correlations of λmax of the d-d transition between 450–540 nm withHammett substituent constants were found in1, and reasonable correlations in2. In methanol a bathochromic shift of this band occurs. An explanation of this phenomenon, partially based on ligand field calculations, is presented.ZusammenfassungDie Elektronenabsorptions-Spektren von zwei Reihen von Ferrocenylchalkonen (Fc-CH=CH-CO-Ar,1 undFc-CO-CH=CH-Ar,2) wurden in Methanol undn-Hexan gemessen. Für1 wurde eine ausgezeichnete Übereinstimmung der λmax-Werte des d-d-Überganges (zwischen 450 und 540 nm) mit denHammett-Substituentenkonstanten gefunden, während sie in der Reihe2 befriedigend ist. In Methanol erleidet die genannte Bande eine bathochrome Verschiebung.Eine Erklärung für diese Ergebnisse wird präsentiert, die zum Teil auf Ligandenfeld-Berechnungen basiert.

Substituent dependence of the d-d transition band in the electronic absorption spectra of arylferrocenes and the corresponding arylferricenium salts

The electronic absorption spectra of 22 arylferrocenes and their arylferricenium salts with pentacyanopropenide (PCNP) were recorded. The attemptedHammett correlation of λmax of the d-d transition bands of arylferrocenes revealed that this band is substituent dependent only for strong electron-withdrawing substituents. Excellent correlation of λmax of the d-d transition bands with σ+ constants was found in the case of arylferricenium cations. Good correlations of λmax was also found with theE1/2 oxidation potentials measured by cyclic voltametry.ZusammenfassungElektronenabsorptions-Spektren von 22 Arylferrocenen und ihren Arylferricenium-Pentacyanopropenid-Salzen wurden gemessen. VersuchteHammett-Korrelationen des längstwelligen d-d-Überganges (λmax) zeigten, daß diese Bande nur von stark elektronenanziehende Substituenten abhängig ist. Im Fall der Arylferricenium-Kationen wurde eine ausgezeichnete Korrelation zwischen λmax der d-d-Bande und den σ+-Konstanten festgestellt. Eine gute Korrelation der λmax-Werte wurde auch mit denE1/2 Oxidationspotentialen gefunden, die durch cyclische Voltametrie meßbar sind.

Ultrasound effects on photochemical reactions. 2. A study of ultrasound effects on some monomolecular and bimolecular photochemical reactions

Abstract The ultrasound effect on two well-described photochemical reaction was studied. Ultrasound does not affect the initiated photoisomerization of 2-phenylindan-1,3-dione to 3-benzylidenephthalide in the case when any additive is present, which is a monomolecular process, but enhances the effect of quenchers on its photoisomerization, which is a bimolecular process. The photodimerization of acenaphthylene is considerably affected by simultaneous sonication, which results in different ratios of the stereoisomers in comparison with the silent process Sonication appears to affect the first reaction by homogeneous distribution of the excited states, or intermediates and possibly by quenching the excited triplet state of the second reaction. Two new reactors were designed allowing simultaneous irradiation of the reaction mixture by UV light and ultrasonic waves.

Spectroscopic study of 2-[2-(4-cyclaminophenyl)ethen-1-yl] benzothiazoles and their N-allylbenzothiazolium bromides. Solvent and substituent effects on their ultraviolet–visible and fluorescence spectra

UV-vis and fluorescence spectra of 2-[2-(4-cyclaminophenyl)ethen-1-yl] benzothiazoles 1 and their N-allylbenzothiazolium bromides 2 have been measured and interpreted. The substitution and solvent effects on electronic structure and spectra have been investigated. The benzothiazolium salts substituted with saturated cyclamines show strong push-pull character and can be used as potential NLO materials. Formation of aggregated structures was observed at higher concentrations of the benzothiazolium bromides.

Effect of reactants’ concentration on the ratio and yield of E,Z isomers of isatin-3-(4-phenyl)semicarbazone and N-methylisatin-3-(4-phenyl)semicarbazone

In this work, the effect of inter- and intramolecular interactions of reactants and products, reactants concentration as well as the solvent effect on the ratio of E and Z isomers of isatinphenylsemicarbazones in the reaction mixture is examined. Theoretical calculations proved that Z isomers are more stable than E isomers. Experimental results confirmed the noncovalent intermolecular donor-acceptor interactions of the reactants in the reaction mixture at concentrations above 0.1 mol L−1. The E/Z isomer ratio of isatin-3-(4-phenyl)semicarbazone (I) and N-methylisatin-3-(4-phenyl)semicarbazone (II) depends on the initial concentrations of 3-amino-1-phenylurea (phenylsemicarbazide; V) and 1H-indole-2,3-dione (isatin; III), or 3-methylindol-2,3(1H)-dion (3-methylisatin; IV), respectively. Both isomers exhibit high thermal stability. Thermal E-Z isomerization takes place at temperatures above 70°C in N,N-dimethylformamide.