New metallomesogens derived from unsymmetric 1,3,4-thiodiazoles: synthesis, single crystal structure, mesomorphism, and optical properties

A series of copper(II) complexes I derived from unsymmetric 1,3,4-thiadiazoles 2 exhibiting mesogenic properties are reported. All the precursors 2 and 3 exhibited smectic A or/and smectic C phases, whereas, copper complexes formed nematic, SmA or SmC phases. The mesophases formed by derivatives 2 and 3 were probably attributed to the H-bondings induced both intramolecularly or/and intermolecularly between amide (-NH) and phenolic (-OH) groups. The crystal and molecular structures of mesogenic 2-(5-(2-(hexyloxy)naphthalene-6-yl)-1,3,4-oxadiazole-2-yl)phenol (2; n=6, m=6) were determined by means of X-ray structural analysis. It crystallizes in the monoclinic space group P-1, with a=7.4255(18) angstrom, b=8.209(2) angstrom, c=17.315(5) angstrom, and Z=2. An intermolecular H-bond (d=1.89 angstrom) between N2 and HIA atoms with an angle of 161.5 degrees was observed. All molecules were packed as tilted layer arrangement and a pi-pi interaction (ca. 3.56 A) was observed. Variable temperature FTIR and H-1 NMR spectroscopies were also used to probe the possible H-bondings formed in compound 2 (m=0, n=6). The fluorescent properties of these compounds 2 were examined. All lambda(max) peaks of the absorption and photoluminescence spectra occurred at ca. 359-363 nm and 519-537 nm, respectively. Excited state intramolecular proton transfer (ESIPT) reaction in this type of ortho-hydroxy-1,3,4-thiadiazole was also observed. (c) 2007 Elsevier Ltd. All rights reserved.