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A new class of discotics derived from tris(N-salicylideneaniline)s have been synthesized and their thermal and photophysical properties are investigated. These systems with outer 1,3,4-oxadiazole wings exist in an inseparable mixture of two keto-enamine tautomeric forms with C(3h) and C(s) rotational symmetries, and self-assemble into fluid columnar phase over a wide thermal range as evidenced by several complementary studies. They possess emissive characteristics in both solution and columnar states; the blue light (lambda = 474 nm) emission has been evidenced for the former state.

We report on measurements of dielectric permittivity epsilon, electrical conductivity sigma, elastic moduli k(ii), and rotational viscosity gamma for a bent-core nematic liquid crystal. The static permittivity anisotropy epsilon(a) = epsilon(parallel)-epsilon(perpendicular) is negative; at a given temperature in the interval 107-123 degrees C, epsilon(parallel) shows two relaxations falling in the frequency bands 20-200 kHz and 0.9-2 MHz; epsilon(perpendicular) also shows a relaxation between 0.9 and 5 MHz. The conductivity anisotropy sigma(a) = sigma(parallel)-sigma(perpendicular) is negative at low frequencies; it changes sign twice at frequencies f(1) and f(2) that increase with temperature, in the ranges 6.5-10 and 95-600 kHz, respectively. Surprisingly, the splay modulus k(11) is considerably greater than the bend modulus k(33) in the entire nematic range. Viscous relaxation is more complex than in calamitic systems involving at least a two-step process. The gamma values are an order of magnitude greater compared to calamitics.

Two series of a unique class of columnar liquid crystals derived from tris(N-salicylideneaniline)s [TSANs] in which the proton and the electron interact with each other through the H-bonding environment are reported. The synthesis is carried out by condensing 1,3,5-triformylphloroglucinol with the respective dialkoxyanilines or trialkoxyanilines. 1H NMR and 1H-1H COSY NMR studies revealed their existence as an inseparable mixture of two keto-enamine tautomeric forms with C3h and Cs rotational symmetries instead of the expected enol-imine form. The influence of the number of peripheral alkoxy tails on the columnar mesomorphic behavior is investigated by using polarizing optical microscopy, differential scanning calorimetry, and X-ray scattering. The fluid/glassy columnar states probed for a number of representative compounds confirmed the D6h (hexagonal) or D2h (rectangular) symmetry of the columns. The electronic absorption and emission characteristics of these compounds have been studied in both mesomorphic and solution states. Of special interest, the photoluminescence spectra of solution and fluid/glassy two-dimensional structure evidently disclose the promising light generating capability of these new discotics systems.

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