UNIGE document Scientific Article
previous document  unige:14383  next document
add to browser collection

Rational tuning of melting entropies for designing luminescent lanthanide-containing thermotropic liquid crystals at room temperature

Escande, Aude
Gumy, Frédéric
Aebischer, Annina
Bünzli, Jean-Claude G.
Donnio, Bertrand
show hidden authors show all authors [1 - 10]
Published in Chemistry - A European Journal. 2007, vol. 13, no. 31, p. 8696-713
Abstract The connection of twelve peripheral and divergent dodecyloxy chains to a central tridentate aromatic binding unit provides the dodecacatenar ligand L11, for which room-temperature mesomorphism is detected. An enthalpically unbalanced large melting entropy (DeltaSmL11=226 J mol(-1) K(-1)) results from the programmed microsegregation induced in the crystalline phase, a phenomenon which is maintained in the associated lanthanide complexes [Ln(L11)(NO3)3] and [Ln(L11)(CF3CO2)3]2. Low-temperature melting processes (-43<or=Tm<or=-25 degrees C) producing room-temperature hexagonal columnar liquid-crystalline phases thus result for these novel lanthanidomesogens. A combined photophysical (high-resolution emission spectroscopy), thermodynamic (differential scanning calorimetry, DSC) and structural (small-angle X-ray diffraction, SA-XRD) investigation of the melting process shows minor structural changes occurring between the crystal (Cr) and the hexagonal columnar mesophase (Colh) in the complexes, which allows the assignment of the existence of these unusual first-order phase transitions to the negligible mixing entropy produced by the two viscous phases at low temperature. Extension of the concept of chemical tuning of melting entropies for the global design of room-temperature metallomesogens and liquid crystals is discussed.
Keywords Crystallography, X-RayEntropyLanthanoid Series Elements/chemistryLigandsLiquid Crystals/chemistryLuminescenceModels, MolecularMolecular StructureOrganometallic Compounds/chemical synthesis/chemistryStereoisomerismTemperature
Stable URL http://archive-ouverte.unige.ch/unige:14383
Full text
Article (Published version) (712 Kb) - document accessible for UNIGE members only Limited access to UNIGE
PMID: 17665377

152 hits

0 download


Deposited on : 2011-02-10

Export document
Format :
Citation style :