Solid-State Functional Materials Based on POSS-core Organic-Inorganic Hybrid Dendrimers

Cubic-octameric polyhedral oligomeric silsesquioxanes (POSS) are interesting materials, in which eight functional groups are appended to the vertices of the three-dimensional, rigid cubic shaped-building blocks. Using POSS cores to synthesize dendrimers is attractive because it requires only a minimal number of synthetic steps; in addition, the polyhedral structures of the POSS core can produce spherically symmetric dendrimers (even with earlier generations) more successfully than conventional cores can. The POSS-cored dendrimers have relatively globular conformations and few entanglements of their branches with high proportion of terminal functional groups positioned on the external surfaces of the dendrimers even in earlier generations. These aspects motivate us that the POSS-core dendrimers terminated with functional units are ideal candidate to construct ordered nano-sized network architecture for solid-state functional materials.

Single Molecular Silsesquoxane Materials

The POSS compounds are used as fillers in matrix polymers and as co-monomers for co-polymerization with organic monomers. Another way of using the POSS compounds contains in the direct cross-linking POSS units with small organic molecules to form three dimension networks. Optical transparent films of a single POSS compound are, however, hardly formed without cross-linking reagents due to their high symmetry and crystallinity. We have proposed that lower the symmetries of the POSS derivatives decrease their crystallinity and provided optical transparent film forming properties. We have shown that dumbbell-shaped trifluoropropyl substituted POSS derivatives and a star-shaped isobutyl-substituted POSS derivative linked by simple aliphatic chains formed optical transparent films. The present molecules are first examples of optical transparent POSS films showing thermoplastic properties. We also demonstrated that dumbbell-shaped POSS derivatives linked by rigid π-conjugated units formed good optical transparent and light-emitting films due to reduction their symmetries and molecular mobility.

Development of Organoarsenic Chemistry Aimed at Emergent Functions

We have reported synthesis of arsenic-containing polymers, poly(vinylene-arsine)s, as first soluble well-defined polymers containing arsenic atoms in the main chain, by ring collapsed radical alternating copolymerization (RCRAC) of cyclooligoarsines and phenylacetylene or its derivatives. We have also synthesized 1,4-dihydro-1,4-diarsinines (DHDA), 1,4-diarsa-1,4-cyclohexadienes, as new cyclic ditopic organoarsenic ligands by radical reaction of pentamethylcyclopentaarsine (cyclo-(MeAs)5) and acetylene derivatives. Our DHDA show unique reactivity and coordination behaviors. During the course of our studies on synthesizing a number of different complexation structures of DHDA to transition metals, we have found that the nonporous crystalline solid of DHDA-Pt(II) complex shows on-off solid-state luminescence switching through reversible and guest-selective uptake and escape. The crystal trapped atmospheric organic vapor molecules such as CH2Cl2, acetone, or toluene despite the absence of large pores in the static solid-state structure.

Organic-Inorganic Composite Nanoparticles Inspired by Biomineralization Process

Construction of organic-inorganic hybrid materials with controlled mineralization is now a current interest for both organic and inorganic chemists to understand the mechanism of natural biomineralization process as well as to seek industrial and technological applications. Most efforts of CaCO3 mineralization have been focused on the influence of specific additives and/or templates on the formation of CaCO3, and then the kinetics and the mechanisms of the subsequently phase transformation and control of morphology. There are, however, little studies applied the specifically binding kinetics and the mechanisms of polyelectrolyte-Ca2+ complexes to the mineralization process of CaCO3 so far. Therefore, the effects of the kinetics and the mechanisms of the interaction of a polymer and Ca2+ on the crystallization process of CaCO3 would provide an opportunity to gain a fundamental understanding on the biomineralization process. We have prepared calcium carbonate composite particles with size-controlled monodispersed spheres by a simple method, “delayed-addition method”.

Organic Conductive Materials Based on Mixed Valence Sate Stacking of π-Conjugated Molecules

Charge-transfer (CT) complexes such as TTF-TCNQ have been known to form conducting crystals consisting of segregated stacks of TTF and TCNQ. They are originated from their mixed-valence state π-stacked columnar structures in their single crystals. We are trying the proposition as to whether the stacking in the mixed valence state of a π-conjugated molecule exhibit the low-dimensional metallic conductivity can be used for the intermolecular interaction. We aim at innovative conjugated organic conductive materials such as conductive nanofibers and conductive films by using new concept and method based on the mixed valence sate stacking.