Synthesis of 3-Substituted Pentane-2,4-Diones: Valuable Intermediates For Liquid Crystals
摘要:
General procedures for the synthesis of six series of 3-substituted pentane-2,4-diones are described. The diones mere used as intermediates in the preparation of pyrazoles, isoxazoles, and coordination complexes whose mesogenic properties have been studied. Nematic and smectic phases have been obtained in a number of cases, and the relationship between molecular structure and mesogenic properties has been explored.
On the Parity in Helical Twisting Power of Ru(III) 1,3-Diketonates of C2 Symmetry in Nematic Liquid Crystals
摘要:
It is demonstrated that the sign of helical twisting power (HTP) of an enantiomeric Ru(III) complex of type [Ru(acac)(2)L] can be switched by choosing L from either L-per or L-para, which is elongated either perpendicular or parallel to the C-2 symmetry axis, and four states become available in combination with Delta Lambda-chirality of the metal center. Complexes 1-n, in which 4,4'-dialkoxylated dibenzoylmethanate ligands are used as L-per, and 2 having L-para = 3-(4'-decyloxyphenyl)pentane-2,4-dionate ligand were prepared for this purpose. They were optically resolved into the enantiomers by means of a clay column chromatography, and their performance as chiral dopants was evaluated in nematic liquid crystals including a room-temperature system, N-methoxybenzylidene-4-n-butylaniline (MBBA), which allowed facile measurements of the helical pitch lengths and CID spectra in the induced chiral nematic states. The induced CID signals have provided a clear evidence for the helical inversion between the two structure types, 1 and 2, of the same chirality. The twisting power of these six-coordinate metal complexes and their structure versus twist sense correlations are interpreted by the shape model. Intrinsically high HTP of Delta-[Ru(acac)(2)L-per] has also allowed for observation of the pitch band due to the selective reflection in the visible wavelength range at the doping level of 2 mol % in MBBA.