Miroslav Ludwig

Solvent and branching effect on the two-photon absorption properties of push–pull triphenylamine derivatives

The photophysical and two-photon absorption (2PA) properties of two tri-podal molecules and of their quadrupolar and dipolar counterparts are reported for a series of solvents with varying polarity. The molecules possess a tri-phenylamine electron donating group and mono-cyano acceptors while olefinic and acetylenic π-linkers have been used. Branching led to an increase of the molar extinction coefficient and to a slight bathochromic shift of the absorption spectra while the fluorescence quantum yields decrease but they are maintained to relatively high values. Solvatochromic measurements in the tri-podal molecules revealed an emitting state with a polar nature. The 2PA cross sections in general increase upon branching but the observed behaviour strongly depends on the type of solvent. The highest 2PA cross sections are obtained in solvents of medium polarity and values as high as 1420 GM are reported.

Convenient methods for preparing π-conjugated linkers as building blocks for modular chemistry

Summary Simple, straightforward and optimized procedures for preparing extended π-conjugated linkers are described. Either unsubstituted or 4-donor substituted π-linkers bearing a styryl, biphenyl, phenylethenylphenyl, and phenylethynylphenyl π-conjugated backbone are functionalized with boronic pinacol esters as well as with terminal acetylene moieties allowing their further use as building blocks in Suzuki–Miyaura or Sonogashira coupling reactions.

Facile Synthesis of Optically Active Imidazole Derivatives

Five optically active imidazole derivatives have been synthesized via a facile 4-step reaction sequence starting from commercially available and inexpensive N-Cbz amino acids. While microwave assisted condensation was unsuccessful, the condensation of the corresponding alpha-bromoketones with formamidine acetate in liquid ammonia was revealed to be a useful method for the synthesis of such imidazole derivatives. The derivatives thus prepared are structurally-related to histamine.

NOVEL CHARGE-TRANSFER CHROMOPHORES FEATURING IMIDAZOLE AS Π-LINKAGE

Overall 21 imidazole-based chromophores have been synthesized and fully characterized. The imidazole core was systematically substituted with donors (NMe 2 and OMe) and acceptors (NO 2 and CN groups) additionally separated from the imidazole by π-spacers such as 1,4-phenylen, styryl or thiophen-2-yl in order to finely tune their intramolecular charge transition. The target chromophores were further investigated by UV/Vis spectroscopy as potentially NLO-active compounds.

Structure-Reactivity-Spectra Correlations for Substituted Benzenesulfonamides

The infrared absorption bands of the S=O and N-H stretching vibrations as well as the natural abundance 13 C and the 17 O NMR chemical shifts were measured for fifteen substituted benzenesulfonamides in CDCl 3 and acetone-d 6 . For the unsubstituted compound the natural abundance 33 S NMR chemical shift was also measured in acetone-d 6 PM3 charge densities and bond orders were calculated for the completely optimised geometry. Mutual correlations are reported between the wave numbers of the asymmetric SO 2 stretching vibration, the arithmetic means of symmetric and asymmetric NH 2 stretching vibrations, Hammett or + substituent constants, dissociation constants, 1 H, 13 C, 15 N and 17 O NMR chemical shifts as well as the PM3 S=O and N-H bond orders and hydrogen, nitrogen and oxygen atom charge densities. The results of the correlation analysis showed that the factors determining the electronic structure and controlling the dissociation equilibria, the IR and NMR spectral properties of substituted benzenesulfonamides must be the same.

3,4-Dinitrothiophene as a central unit of quadrupolar push-pull-push systems

3,4-Dinitrothiophene has been utilized as a central acceptor unit in quadrupolar D-π-A-π-D push-pull-push chromophores. Employing cross-coupling and Knoevenagel reactions, nine novel chromophores bearing terminal methoxythiophene donor and systematically extended/varied π-linker were synthesized. Optical properties were studied by electronic absorption spectra. Fundamental optoelectronic properties were investigated by semiempirical PM7 calculations. It was shown that by varying the π-conjugated system the longestwavelength absorption maxima can be shifted from 341 to 489 nm. The calculated HOMO–LUMO gaps were found within the range of 6.69–7.29 eV, while the second-order molecular polarizabilities can be tuned from 0.038 to 1.578 × 10–27 esu.

Structure-Acidity-IR Spectra Correlations for p-Substituted N-Phenylsulfonylbenzamides †

The wavenumbers of the IR absorption bands of the C=O, S=O and N-H stretching vibrations for a series of p-substituted N-phenylsulfonylbenzamides were measured in trichloromethane. The bond orders, Mulliken charges, charge densities and heats of formation were calculated using the PM3 method. Fifty significant mutual mono parameter (MP) and six dual parameter (DP) correlations were found for the IR spectral, theoretical structural data, substituent constants and previously reported dissociation constants in five polar organic solvents. The transmission of the substituent effects has been discussed and the solvent effect on the slopes of some linear correlations was evaluated using different solvent parameters. The results showed that the factors describing the electronic structure and controlling the dissociation equilibrium and the IR spectra properties of p-substituted N-phenylsulfonylbenzamides must be the same.

Relationship between the morphology of maghemite and the properties of magnetic tapes

Abstract Ludwig, M., Halova, J., Subrt, J., Tlaskal, J. and Žak, P., 1993. Relationship between the morphology of maghemite and the properties of magnetic tapes. Chemometrics and Intelligent Laboratory Systems , 18: 221–227. An intelligent laboratory system for the determination of the relationship between maghemite morphology and the electroacoustic properties of magnetic tapes has been validated. Electron micrographs were evaluated with a TAS-Leitz image analyzer and structure-property relationships were determined by projection to latent structures and principal component analysis methods. The results of the computation show that the electroacoustic properties of a tape are mainly determined by the length of the maghemite particles. This conclusion is in good agreement with the empirical fact that acicular maghemite particles are the best ones for the production of magnetic tapes. The other results also correspond with experience and so the intelligent laboratory system for materials research on maghemite has been validated.