Liquid crystal behavior induced in highly luminescent unsymmetrical borondifluoride β-diketonate materials

Abstract

Highly luminescent and liquid crystal materials were successfully prepared by the strategic introduction of unsymmetrically alkyloxyphenyl substituted β-diketones, as ligands towards the BF2 group. So, four families of ligands and their boron derivatives were prepared, each of them containing invariable the alkyl chain at one of the substituents in the 1(3) position, with 12, 14, 16 or 18 carbon atoms, while for the other substituent at the 3(1) position, the number of alkyl carbon atoms was increased from 4 to 18. In this way, the influence of factors as asymmetry or molecular length was evaluated towards the liquid crystal behavior of the compounds.The photophysical characterization of the boron derivatives was also carried out, showing in all cases a high fluorescent emission in the blue–violet region in solution and in the green region in the solid state, with quantum yields near the unity. In addition, thermal studies by DSC, as well as the analysis by POM and XRD were determinant to characterize the compounds as liquid crystal materials, exhibiting B1 mesophases, in agreement with the banana molecular shape. In contrast the corresponding β-diketone precursors behave again as liquid crystals showing SmC and N mesophases.