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

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  Escande,A., Guenee,L., Nozary,H., Bernardinelli,G., Gumy,F.,   Aebischer,A., Bunzli,J.C.G., Donnio,B., Guillon,D., Piguet,C.   Chemistry-A European Journal 2007  13 (31) 8696-8713

  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 (Delta S-m(L11) = 226 J   mol(-1)K(-1)) results from the programmed microsegregam tion   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 <= T-m <= -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   (Col(h)) 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

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