Rational tuning of melting entropies for designing luminescent lanthanide-containing thermotropic liquid crystals at room temperature.
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.
Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, 30 quai E. Ansermet, -1211 Geneva 4, Switzerland.
Aude
A
Escande
Laure
L
Guénée
Homayoun
H
Nozary
Gérald
G
Bernardinelli
Frédéric
F
Gumy
Annina
A
Aebischer
Jean-Claude G
JC
Bünzli
Bertrand
B
Donnio
Daniel
D
Guillon
Claude
C
Piguet
D018360:Crystallography, X-Ray; D019277:Entropy; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008024:Ligands; D050866:Liquid Crystals / Q000737:chemistry*; D049449:Luminescence; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism; D013696:Temperature
D028581:Lanthanoid Series Elements; D008024:Ligands; D009942:Organometallic Compounds