The synthesis of C3‐symmetrical tristriazolotriazines with conjugated arms and lateral alkoxy side chains was performed by a threefold condensation of cyanuric chloride with tetrazoles. Conjugated π segments include phenyl, tolane, and its phenylethynyl‐elongated homologue. Disclike and a dendritic molecule have been obtained, and two compounds with a 3,4,5‐tris(octyloxy) substitution form broad thermotropic mesophases. The linear optical properties, solvatochromism of the fluorescence, acidochromism, and the two‐photon absorption efficiency of selected compounds are reported.
Selenium(II) dimethanethiolate, Se(SMe)(2), was synthesized by reaction of SeO(2) with HSMe. Basic spectroscopic data for Se(SMe)(2) and selenium(II) bis(2-methyl-2-propanethiolate), Se(S(t)Bu)(2), were recorded and interpreted with the support of ab initio calculations. Both compounds are thermodynamically unstable relatively to selenium and the corresponding disulfide. The UV/vis spectra of both compounds are qualitatively similar, the two bands being attributed to n(Se)-sigma*(Se-S) transitions. The bands at 369 and 397 cm(-1) in the IR spectra of Se(SMe)(2) and Se(S(t)Bu)(2), respectively, are assigned to nu(as)(SeS(2)). The (77)Se NMR shifts of Se(SMe)(2)(784 ppm) and Se(S(t)Bu)(2)(556 ppm) differ substantially from each other and show positive temperature gradients. Calculations at the GIAO-HF/962+(d) level reproduced the difference of the (77)Se NMR chemical shifts between Se(SMe)(2) and Se(S(t)Bu)(2). At the same level, the effect of conformational changes on (77)Se shifts were studied for Se(SMe)(2). In the solid state Se(SMe)(2) forms long intermolecular SeS contacts while Se(S(t)Bu)(2) does not. Both compounds exhibit anti-conformations of the methyl and tert-butyl groups with respect to the SeS(2) plane. MP2/LANL2DZ(d) geometry optimizations, single point energy and frequency calculations performed for Se(SMe)(2) show, that syn- (C(s)) and anti-conformers (C(2)) represent minima on the potential energy surface, the latter being by 8 kJ mol(-1) lower in energy than the former. Both conformers are stabilized by intramolecular pi-type n(S(1))-sigma*(Se-S(2)) orbital interactions. The energy of the transition state for the mutual conversion of the two conformers was calculated to be 31 kJ mol(-1) above that of the syn conformer, allowing a rapid interconversion of the two conformers at room temperature. Intermolecular interactions between Se(SMe)(2) molecules were also studied by means of calculations at the MP2/LANL2DZ(d) level. For Se(S(t)Bu)(2) MP2/LANL2DZ(d) geometry optimizations and single point energy calculations revealed a C(2)-symmetric anti- and a C(1) symmetric syn-conformer, the latter being 21 kJ mol(-1) higher in energy than the former. Se(SMe)(2) and Se(S(t)Bu)(2) exchange thiolate groups with other selenium(II) dithiolates, tellurium(II) dithiolates and with thiols, if catalytic amounts of p-CH(3)C(6)H(4)SO(3)H are added.
Tristriazolotriazines with a threefold 3,5-dialkoxyphenyl substitution were prepared from the corresponding phenyltetrazoles and cyanuric chloride. These star-shaped compounds are discotic liquid crystals that form broad and stable thermotropic mesophases. The thermal behaviour was studied by DSC and polarizing optical microscopy. An increasing length of the side chains reduces the phase transition temperatures, this effect is more pronounced for the crystalline to mesophase transition than for the clearing temperature. XRD on an oriented sample revealed a hexagonal columnar structure for the mesophase. All TTTs emit a strong fluorescence in the UV-violet region.
Tristriazolotriazines (TTTs) with a threefold alkoxyphenyl substitution were prepared and studied by DSC, polarized optical microscopy (POM) and X-ray scattering. Six pentyloxy chains are sufficient to induce liquid-crystalline behavior in these star-shaped compounds. Thermotropic properties of TTTs with varying substitution patterns and a periphery of linear chains of different lengths, branching in the chain and swallow-tails, are compared. Generally, these disks display broad and stable thermotropic mesophases, with the tangential TTT being superior to the radial isomer. The structure–property relationships of the number of alkyl chains, their position, length and structure were studied.
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