No abstract available

[en] The effects of hydrogen bonding, inter- and intramolecular electrostatic interactions on the conformation of trigonellinium chloride, TRGH...Cl, in the crystal and on that of a single molecule have been studied by X-ray diffraction, FT-IR, Raman, ¹H and ¹³C NMR spectroscopies, and by MP2 and DFT calculations. In the crystal, the Cl^- anion is connected with protonated trigonelline via hydrogen bond, O-H...Cl^-=2.915(3) Angst, and three N⁺...Cl^- intermolecular electrostatic interactions. In a single molecule, the Cl^- anion is also engaged in a slightly longer hydrogen bond, O-H...Cl^-=2.948-3.019 Angst, but only in one type of intramolecular electrostatic interaction. The optimized bond lengths and bond angles at the MP2 and B3LYP levels of theory are in good agreement with the X-ray data, except conformation of the COOH group, which is cis (syn) in the crystal and trans (anti) in the single molecule. The probable assignments for the experimental solid state vibrational spectra of TRGH.Cl and TRGD.Cl based on the calculated MP2/cc-pVDZ frequencies and intensities were made. The effect of quaternization of nicotinic acid, its salt and amide on chemical shifts of the ring protons and carbons is analyzed

No abstract available

[en] A series of styryl-carbazole derivatives (with and without a silicon atom) were investigated in n-hexane and in acetonitrile in terms of their spectroscopic and photophysical properties. The major question addressed in this work is how the presence of a trimethylsilyl group modifies the absorption and emission properties of styryl-carbazoles depending whether vinyl groups are in a meta- or para- position. It was observed that only para-styryl-carbazole containing silicon undergoes a solvent-induced inversion of its lowest singlet excited states whereas meta-styryl-carbazole containing silicon retains the properties of the meta-styryl-carbazole itself. The different character of the emissive state was deduced from its 7-fold larger radiative rate constant in acetonitrile compared to results in n-hexane. DFT calculations revealed on the molecular level why inversion of the excited states occurs only for this silicon-based styryl-carbazole whose vinyl group is in the para- and not in the meta- position.