Rational Tuning of Melting Entropies for Designing Luminescent Lanthanide‐Containing Thermotropic Liquid Crystals at Room Temperature

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.

A quantitative assessment of chemical perturbations in thermotropic cyanobiphenyls

“…8b). 32 When subjected to CFED analysis ( Fig. 9), unusually small absolute cohesive entropy densities are computed in the solid state 0.11 r |S CFED | = (qCFED/qT) P r 0.13 J K À1 cm 3 (Fig.…”

Mesomorphism and Photophysics of Some Metallomesogens Based on Hexasubstituted 2,2′:6′, 2′′‐Terpyridines

“…It is found that shows aC ol h phase as evidenced by the observation of both a ( 10) and (11) reflection, with evidence for aE u···Eu correlation at 7 and as tacking period of 3.6 . The observation of the stacking period is interesting in comparison to some of the observations above as the ligand here contains the fused C 5 rings and the metal bears the three bulky k 2 -nitrato ligands, which would imply some sort of backto-back arrangement of the complexes in the mesophase.…”

“…Twor epresentative zinc(II)-terpyridine complexes with hexadecyl chains werec hosen for preliminary photophysical studies, one with (10)(11)(12)(13)(14)(15)(16) and one without (11)(12)(13)(14)(15)(16) af used cyclopentene ring. Absorption and emission studies were carried out in solvents of varying polarity and data are collected in Ta ble 4.…”

“…Liquid crystals represent materials with inherent order that could lead to preferred conduction pathways (lower display drive voltages) or polarised emission, and their fluid nature gives the potential for self healing. However, while square‐planar Pt II complexes are rather readily modified to give liquid crystal phases, elements requiring higher coordination numbers (Ir III , lanthanides) represent a different level of challenge ,,…”

Europium‐containing cholesteric liquid crystalline polymers in the side chain

“…In the last decade, a substantial amount of research has been devoted to design luminescent liquid crystals to obtain the materials that combine the properties of liquid crystals and rare earth complexes . Most examples of lanthanidomesogens are smectic liquid crystals, which mimicked the disk‐like or rod‐like shape of the conventional organic liquid crystals and some examples of lyotropic lanthanidomesogens have also been reported . However, the high transition temperatures, unworkability, and low thermal stability are major drawbacks that hamper the application of the physical properties of these materials.…”