Masaki Yamamura

Phosphorus-containing chiral molecule for fullerene recognition based on concave/convex interaction.

A C3-symmetric chiral concave molecule having a phosphorus atom at the center was synthesized, and its enantiomers were resolved. The chiral concave shape and absolute structure of the concave molecules were revealed by X-ray analysis. The concave molecule exhibited intense chiroptical properties with a large anisotropy, which was derived from molecular orbitals delocalized to the side chains. In the co-crystal with pristine C60, four of the enantiopure concave molecules perfectly wrapped the surface of C60. MALDI-TOF mass, NMR, and circular dichromism spectra also supported the concave/convex interaction between the concave molecule and fullerene. These results suggest that the phosphorus-containing molecule with a concave shape plays an important role as a chiral host molecule for C60.

Ratiometric fluorescence detection of anions by silanediol-based receptors bearing anthryl and pyrenyl groups.

Two silanediol derivatives bearing 9-anthryl (2) and 1-pyrenyl (3) groups have been developed for fluorescence detection of anions. Receptor 3 showed favorable ratiometric response by fluorescence spectroscopy upon the addition of biologically relevant anions, such as acetate and dihydrogen phosphate in acetonitrile.

Nuclearity control of a trisaloph zinc cluster complex dependent on minute structural differences in the bridging anions.

The Zn(6) cluster complex 2 of the trisaloph ligand was synthesized using EtCO(2)(-) anions as bridging ligands. Complex 2 has a dimeric structure in the crystalline state, while two monomeric isomers were in equilibrium in solution. The anion-exchange reaction successfully resulted in nuclearity control from Zn(7) to Zn(6).

Red/Near-Infrared Luminescence Tuning of Group-14 Element Complexes of Dipyrrins Based on a Central Atom

A dipyrrin complex has been one of the most utilized fluorescent dyes, and a variety of dipyrrin complexes show intriguing functions based on the various coordination structures of the central element. We now report the synthesis, structure, and photophysical properties of germanium and stannane complexes of the N2O2-type tetradentate dipyrrin, L·Ge and L·Sn, which are heavier analogues of the previously reported dipyrrin silicon complex, L·Si. The central group-14 atoms of the monomeric complexes have geometries close to trigonal bipyramidal (TBP), in which the contribution of the square-pyramidal (SP) character becomes higher as the central atom is heavier. Interestingly, L·Sn formed a dimeric structure in the crystal. All complexes L·Si, L·Ge, and L·Sn showed a fluorescence in the red/NIR region. Fluorescence quantum yields of L·Ge and L·Sn are higher than that of L·Si. These results indicated that the central atom on the dipyrrin complexes contributes not only to the geometry difference but also to tuning the fluorescence properties.

Synthesis and Chiroptical Properties of a Ring-Fused BODIPY with a Skewed Chiral π Skeleton.

A twisted chiral boron-dipyrrin complex (BODIPY) was synthesized by oxidative annulation of the biphenyl units at the β positions. The chiral BODIPY has two asymmetric carbons in the large planar skeleton, which were generated upon the ring-fused reaction. Its π-elongated and twisted structure resulted in the Cotton effect in the red region (λmax = 614 nm, Δε = 60 M(-1)·cm(-1)) as well as the strong fluorescence (ΦF = 0.73) and circularly polarized luminescence (CPL).

Detection of ethanol in alcoholic beverages or vapor phase using fluorescent molecules embedded in a nanofibrous polymer.

An alcohol sensor was developed using the solid-state fluorescence emission of terphenyl-ol (TPhOH) derivatives. Admixtures of TPhOH and sodium carbonate exhibited bright sky-blue fluorescence in the solid state upon addition of small quantities of ethanol. A series of terphenol derivatives was synthesized, and the effects of solvent polarities and the structures of these π-conjugated systems on their fluorescence were systematically investigated by using fluorescence spectroscopy. In particular, π-extended TPhOHs and TPhOHs containing electron-withdrawing groups exhibited significant solvatochromism, and fluorescence colors varied from blue to red. Detection of ethanol contents in alcohol beverages (detection limit ∼ 5 v/v %) was demonstrated using different TPhOHs revealing the effect of molecular structure on sensing properties. Ethanol contents in alcoholic beverages could be estimated from the intensity of the fluorescence elicited from the TPhOHs. Moreover, when terphenol and Na2CO3 were combined with a water-absorbent polymer, ethanol could be detected at lower concentrations. Detection of ethanol vapor (8 v/v % in air) was also accomplished using a nanofibrous polymer scaffold as the immobilized sensing film.

Synthesis of Phosphorus-Centered and Chalcogen-Bridged Concave Molecules: Modulation of Bowl Geometries and Packing Structures by Changing Bridging Atoms

A series of phosphorus-centered concave molecules having oxygen and sulfur as bridging atoms, C3v-symmetric P4 and Cs-symmetric P2 and P3, were newly synthesized. The packing diagrams of the concave molecules P1-P4 are dependent on the bridging atoms, columnar structures for P1 and P4, and zigzag structures for P2 and P3. The bowl depth becomes shallower in the order of P1, P2, P3, and P4 as the number of bridging sulfur atoms increases.

Cooperative formation and functions of multimetal supramolecular systems

Multimetal complexes provide a variety of interesting structures, unique properties, and functions. Such sophisticated functions are often produced by synergistic and cooperative interactions among the metal ions accumulated in the restricted small area of the multimetal systems. We describe novel three strategies (i.e., macrocyclic, C-shape, and multimetal template) for the preparation of the multimetal supramolecular systems by the cooperative metal binding of a multi-Schiff-base and multi-oxime ligands, and their characteristic structures and functions. The three approaches are versatile and effective because the employed coordination reactions smoothly and quickly proceeded under mild conditions to quantitatively form the desired coordination structures. The multimetal supramolecular systems obtained here exhibit the synergistic and cooperative functions for ion recognition, magnetic properties, helicity control, and modulation of reaction selectivity. These types of multimetal complexes could be developed for a cascade functional supramolecular system that shows highly synergistic properties, integrated multifunctions, and function amplification.

Coordination-Driven Macrocyclization for Locking of Photo- and Thermal cis→trans Isomerization of Azobenzene

Both trans and cis isomers of azobenzene-linked bis-terpyridine ligand L1 were incorporated in rigid macrocycles linked by Fe(II) (tpy)2 (tpy: terpyridine) units. The complex of the longer trans-L1 is dinuclear [(trans-L1)2 ⋅Fe(II) 2 ], whereas the complex of the shorter cis-L1 is mononuclear [cis-L1⋅Fe(II) ]. The complex cis-L1⋅Fe(II) was not only thermally stable but also photochemically inactive. These results indicate a perfectly locked state of cis-azobenzene. The stable macrocyclic structure of cis-L1⋅Fe(II) causes locking of the isomerization. To the best of our knowledge, this is first example of dual locking of photo- and thermal isomerization of cis-azobenzene.

A Hierarchical Self-Assembly System Built Up from Preorganized Tripodal Helical Metal Complexes

The hierarchical organization strategy has realized elaborate supramolecular structures that are difficult to achieve by a one-pot thermodynamically driven self-assembly. Self-assembly via Schiff base formation of the preorganized tripodal helical unit 2(2+), which is composed of the tris(bipyridyl) ligand 1 and octahedral metal ion (Ru(II) and Fe(II)), lead to two supramolecular structures, i.e., a macrobicyclic dimer and an interlocked helicate. Notably, the interlocked helicate had a unique motif with an elongated shape (∼ 58 Å) and linearly aligned metal centers with homochiral configurations (all-Δ or all-Λ), which shows potential for allosteric regulation based on the long-range transmittance of the structural information.