H-bonded effects on supramolecular liquid crystalline trimers containing photoluminescent cores

Several series of hydrogen-bonded (H-bonded) liquid crystalline trimers are constructed by complexation of two complementary components containing various bifunctional photoluminescent (PL) acceptor cores and monofunctional proton donors (in a 1 : 2 molar ratio). These supramolecular liquid crystalline trimers (i.e. H-bonded trimers 1/3, 1/4, 1/5, 1/6, 2/3, 2/4, 2/5 and 2/6) are, respectively, obtained from bifunctional bis-pyridyl acceptors (containing conjugated benzene and thiophene centers) (1 and 2) complexed with monofunctional carboxylic acids (containing benzene, thiophene or naphthalene) (3-6) in a 1 : 2 acceptor-donor group stoichiometry. Though the PL bis-pyridyl acceptors (1 and 2) do not possess any mesophases, the distinct mesomorphism and supramolecular architecture of these H-bonded trimers are confirmed by polarizing optical microscopy (POM), DSC, and powder X-ray diffraction (XRD) experiments. Moreover, the PL properties of the photoluminescent bis-pyridyl cores can be adjusted not only by the central structures of the cores but also by their surrounding non-photoluminescent proton donors. In general, redder shifts occur in PL spectra of H-bonded trimers when proton donors of smaller pK(a) values are H-bonded to the photoluminescent cores. Significantly, different wavelengths and polarized light of PL emission can be obtained in these supramolecular structures possessing both liquid crstalline and photoluminescent properties.