ABSTRACT
Since the discovery of unusual thermal behavior of cholesteryl benzoate over 120 years ago,1 the ™eld of liquid crystals (LCs) has grown to an impressive size, and its signi™cance in contemporary technologies is apparent. More than a century of research has resulted in nearly 100,000 organic, organometallic, ionic, and polymeric compounds characterized as thermotropic LCs.2 With respect to their molecular shapes, these compounds are divided into several classes, which include calamitic (or rod-like, Figure 14.1a), bent-core (Figure 14.1b), and discotic, and they form nematic, smectic (lamellar), banana, and columnar types of supramolecular structures (Figure 14.2).3−5
14.1 Introduction .......................................................................................................................... 319 14.2 closo-Boranes ....................................................................................................................... 321 14.3 Liquid Crystalline Derivatives of closo-Boranes ................................................................. 326 14.4 Structural Effects on Thermal Properties ............................................................................ 331
14.4.1 Derivatives of p-Carboranes ..................................................................................... 332 14.4.1.1 Homologous Series .................................................................................... 332 14.4.1.2 Linking Group L ........................................................................................ 333 14.4.1.3 Terminal Connector C ............................................................................... 334 14.4.1.4 Lateral Substituent Z .................................................................................. 335 14.4.1.5 Terminal Chain Fluorination X = RF .......................................................... 336
14.4.2 Derivatives of m-Carboranes .................................................................................... 337 14.4.3 Derivatives of closo-Monocarbaborates ................................................................... 338
14.4.3.1 Polar Derivatives ........................................................................................ 338 14.4.3.2 Ionic Liquid Crystals ................................................................................. 339
14.4.4 Derivatives of closo-Decaborate............................................................................... 339 14.4.5 Derivatives of Bis(tricarbollide)Fe(II) ......................................................................340
