Pavol Zahradník

Benzothiazoles with Tunable Electron-Withdrawing Strength and Reverse Polarity: A Route to Triphenylamine-Based Chromophores with Enhanced Two-Photon Absorption

A series of dipolar and octupolar triphenylamine-derived dyes containing a benzothiazole positioned in the matched or mismatched fashion have been designed and synthesized via palladium-catalyzed Sonogashira cross-coupling reactions. Linear and nonlinear optical properties of the designed molecules were tuned by an additional electron-withdrawing group (EWG) and by changing the relative positions of the donor and acceptor substituents on the heterocyclic ring. This allowed us to examine the effect of positional isomerism and extend the structure-property relationships useful in the engineering of novel heteroaromatic-based systems with enhanced two-photon absorption (TPA). The TPA cross-sections (δ(TPA)) in the target compounds dramatically increased with the branching of the triphenylamine core and with the strength of the auxiliary acceptor. In addition, a change from the commonly used polarity in push-pull benzothiazoles to a reverse one has been revealed as a particularly useful strategy (regioisomeric control) for enhancing TPA cross-sections and shifting the absorption and emission maxima to longer wavelengths. The maximum TPA cross-sections of the star-shaped three-branched triphenylamines are ∼500-2300 GM in the near-infrared region (740-810 nm); thereby the molecular weight normalized δ(TPA)/MW values of the best performing dyes within the series (2.0-2.4 GM·g(-1)·mol) are comparable to those of the most efficient TPA chromophores reported to date. The large TPA cross-sections combined with high emission quantum yields and large Stokes shifts make these compounds excellent candidates for various TPA applications, including two-photon fluorescence microscopy.

Benzothiazole-Based Fluorophores of Donor−π-Acceptor−π-Donor Type Displaying High Two-Photon Absorption

A series of novel heterocycle-based dyes with donor-pi-bridge-acceptor-pi-bridge-donor (D-pi-A-pi-D) structural motif, where benzothiazole serves as an electron-withdrawing core, have been designed and synthesized via palladium-catalyzed Sonogashira and Suzuki-type cross-coupling reactions. All the target chromophores show strong one-photon and two-photon excited emission. The maximum two-photon absorption (TPA) cross sections delta(TPA) of the prepared derivatives bearing diphenylamino functionalities occur at wavelengths ranging from 760 to 800 nm and are as large as approximately 900-1100 GM. One- and two-photon absorption characteristics of the title dyes have also been investigated by using density functional theory (DFT) and the structure-property relationships are discussed. The TPA cross sections calculated by means of quadratic response time-dependent DFT using the Coulomb-attenuated CAM-B3LYP functional support the experimentally observed trends within the series, as well as higher delta(TPA) values of the title compounds compared to those of analogous fluorene or carbazole-derived dyes. In contrast, the traditional B3LYP functional was not successful in predicting the observed trend of TPA cross sections for systems with different central cores. In general, structural modification of the pi-bridge composition by replacement of ethynylene (alkyne) with E-ethenylene (alkene) linkages and/or replacement of dialkylamino electron-donating edge substituents by diarylamino ones results in an increase of delta(TPA) values. The combination of large TPA cross sections and high emission quantum yields makes the title benzothiazole-based dyes attractive for applications involving two-photon excited fluorescence (TPEF).

Computational design of benzothiazole-derived push–pull dyes with high molecular quadratic hyperpolarizabilities

Semi-empirical ZINDO SOS and ab initio quadratic response function (DDRPA) calculations on a series of donor–acceptor substituted π-conjugated chromophores based on styryl benzothiazoles are used to aid in the design of dyes with high non-linear optical properties. Structural modifications studied include nature and position of the donor and/or acceptor group as well as the length of the connecting π-bridge. The most worthwhile target for synthesis are 2-tricyanovinyl-6-p-donor-styryl benzothiazoles and heteroaryl derivatives thereof.

Anomalies in the gas chromatographic behaviour of substances facilitating a ring conformation through their propyl group

Abstract The applicability of precise gas chromatogaphic measurements has been demonstrated for the identification of very fine structural features of compounds. On the basis of the gas chromatographic behaviour of five classes of unsaturated hydrocarbons and four classes of compounds containing hetero-atoms, it is concluded that retention anomalies are to be expected for compounds with molecular structures that make it possible to form a ring conformation of the propyl group with the π-electron system of the remainder of the molecule and that this phenomenon is a common feature of the compounds with such structures.

Basis set and electron correlation effects on static electric properties of 1,3-thiazoles and 1,3-benzothiazoles as potential fragments in push-pull NLO chromophores

Dipole moments μ, static averaged polarizabilities ⟨αrang;, and hyperpolarizabilities βvec of thiazole, benzothiazole, and their dipolar substituted derivatives have been computed by means of B3LYP and MP2 theories with the Pol basis set. Basis set effects have been considered for thiazole, benzothiazole, and doubly substituted thiazole and benzothiazole derivatives at the B3LYP level of theory and in the case of thiazole also at the HF and MP2 levels. Attention has been paid to thiazole geometry effects on the electric properties. The effectiveness of thiazole and benzothiazole as a conjugative pathway between electron donor NH2 and electron acceptor NO2 substituents has been compared with benzene. With one exception, differences in geometry appear to influence only modestly the calculated electric properties. The dipole moment- and polarizability-oriented Sadlej Pol basis set and also its reduced form ZPol basis sets are able to reproduce the aug-cc-pVTZ generated μ, ⟨αrang;, and also βvec at all levels of theory (HF, B3LYP, and MP2) very satisfactorily. All approaches yield almost identical basis set trends. A very good agreement in ⟨αrang; values between the B3LYP and MP2 approach has been found. While the doubly substituted thiazole derivatives possess smaller βvec calculated at the B3LYP level than at the MP2 level, for doubly substituted benzothiazole derivatives the B3LYP estimates of βvec exceed the MP2 estimates. The trends established by the B3LYP functional parallel the trends obtained with the MP2 method. The 2-nitrobenzothiazole-6-amine and 6-nitrobenzothiazole-2-amine exhibit the largest electric properties from the investigated set of molecules. Thiazole (benzothiazole) as a bridging unit between NH2 and NO2 shows slightly reduced (enhanced) NLO characteristic than pNA. Thiazole behaves as a dipolar bridge rather than just an electron acceptor substituent in singly substituted derivatives. Concerning the charge transfer process, NO2 group interacts better with thiazole than NH2, which can result from the tendency to pyramidization of the NH2 group.

Neural Network Approach to the Prediction of the Toxicity of Benzothiazolium Salts from Molecular Structure

The prediction of the toxicity of benzothiazolium salts calculated by the neural network model is presented. The results are comparable with the previous calculations based on the Free--Wilson additivity model. The method of calculation of activity contributions of substituents is described.

Chemogenomic and transcriptome analysis identifies mode of action of the chemosensitizing agent CTBT (7-chlorotetrazolo[5,1-c]benzo[1,2,4]triazine).

BackgroundCTBT (7-chlorotetrazolo [5,1-c]benzo[1,2,4]triazine) increases efficacy of commonly used antifungal agents by an unknown mechanism. It increases the susceptibility of Saccharomyces cerevisiae, Candida albicans and Candida glabrata cells to cycloheximide, 5-fluorocytosine and azole antimycotic drugs. Here we elucidate CTBT mode of action with a combination of systematic genetic and transcriptome analysis.ResultsTo identify the cellular processes affected by CTBT, we screened the systematic haploid deletion mutant collection for CTBT sensitive mutants. We identified 169 hypersensitive deletion mutants. The deleted genes encode proteins mainly involved in mitochondrial functions, DNA repair, transcription and chromatin remodeling, and oxidative stress response. We found that the susceptibility of yeast cells to CTBT depends on molecular oxygen. Transcriptome analysis of the immediate early response to CTBT revealed rapid induction of oxidant and stress response defense genes. Many of these genes depend on the transcription factors Yap1 and Cin5. Yap1 accumulates rapidly in the nucleus in CTBT treated cells suggesting acute oxidative stress. Moreover, molecular calculations supported a superoxide generating activity of CTBT. Superoxide production in vivo by CTBT was found associated to mitochondria as indicated by oxidation of MitoSOX Red.ConclusionWe conclude that CTBT causes intracellular superoxide production and oxidative stress in fungal cells and is thus enhancing antimycotic drug effects by a secondary stress.

Infrared spectra and theoretical study of methyl, formyl and acetyl derivatives of chromones

SummaryThe C=O stretching frequencies of substituted 2-methylchromones (3a–3j), 2-formylchromones (4a–4j), 3-formylchromones (5a–5j) and 3-acetyl-2-methylchromones (6a–6i) were measured in CCl4 and CHCl3 and correlated with σ+ substituent constants. Using the results of the infrared spectral investigation and the theoretical calculations by the semiempirical AM1 method, the conformation and the transmission of electronic effects in compounds4–6 were studied. For the 2-substituted chromone system the transmission factory γ according to the definition of Charton was determined. The preparation of some new 2-methylchromones (3e–3j) and 3-(2,2-diformyl-chlorovinyl)-6-methylchromone (7) is also described.ZusammenfassungEs wurden die C=O-Streckschwingungsfrequenzen von substituierten 2-Methyl-chromonen (3a–3j), 2-Formylchromonen (4a–4j), 3-Formyl-chromonen (5a–5j) und 3-Acetyl-2-methylchromonen (6a–6j) in CCl4 und CHCl3 gemessen und mit den σ+-Substituenteknonstanten korreliert. Unter Verwendung der IR-Resultate und theoretischer Behandlung mit Hilfe semiempirischer AM1-Rechnungen wurden die Konformationen und die Transmission elektronischer Effekte in den untersuchten Verbindungen4–6 untersucht. Für die 2-substituierten Chromon-Systeme wurde der Transmissionsfaktor γ entsprechend der Definition von Charton bestimmt. Die Herstellung einiger neuer 2-Methylchromone (3e–3j) und 3(2,2-Diformyl-1-chlorvinyl)-6 methylchromon (7) wird ebenfalls beschrieben.

New conjugated benzothiazole-N-oxides: synthesis and biological activity.

Eleven new 2-styrylbenzothiazole-N-oxides have been prepared by aldol – type condensation reactions between 2-methylbenzothiazole–N-oxide and para-substituted benzaldehydes. Compounds with cyclic amino substituents showed typical push-pull molecule properties. Four compounds were tested against various bacterial strains as well as the protozoan Euglena gracilis as model microorganisms. Unlike previously prepared analogous benzothiazolium salts, only weak activity was recorded.

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.