Mesogenic Materials Containing Main Group Borondifluorides( I )

Metallomesogens, i.e. metal-containing liquid crystals have been our research focus during the past years. Recently, our research target has been slightly shifted to mesogenic materials containing main group 13 (or IIIB) elements. Complexes or adducts containing boron difluoride (BF2) have received much attention during the past years. Many known BF2 complexes, widely investigated as fluorescent materials have shown the potential applications in many areas such as biological imaging, molecular probes, electroluminescent devices, photo- sensitizes and others. These complexes were often generated by reactions of BF3 and conjugated chelating ligands. Boron, a nonmetal element of Group 13 (IIIA), is considered as an electron deficient atom. It has an oxidation state of three and the most complexes all form a triangular or tetrahedral geometry. Many unique boron complexes have been reported and their optical properties were extensively investigated. Three types of coordination modes, i.e. B-[O,O], B-[N,O] and B-[N,N0], have long been known for core boron. The majority of BF2 complexes were coordinated with O,O-chelating ligands, such as diketonates and triketonates. Recently, much attention has been paid to such BF2-[O,O] complexes, when studied in applications of two-photo absorbing molecules, luminescent materials, sensors and near-IR probes. In contrast, rarer complexes coordinated to N,N-chelating ligands were known, such as diketiminates and formazanates. Only a few complexes were known to complex with N,O-chelating ligands, such as quinolone-ketones. These BF2-[N,O] complexes often showed interesting photophysical and photochemical properties, which might have applications in OLED, OFET, LCs and others. The diketiminate and formazanate moieties were considered as redox-active and nearinfrared dyes that showed larger Stokes shifts upon complexation to boron from heterocyclic compounds. Boron complexes containing mono-BF2 and bis-BF2 moieties will be continuously studied. Columnar and smectic phases are expected to exhibit by these boron complexes depending the shape of the molecules. In addition, their optical properties will be also explored in detail. A few novel structures containing tris-(BF2)3 will be prepared in this proposal,