TiO₂-based dye-sensitized solar cells (DSSCs) have been widely recognized as one of the most promising photovoltaic cells because of their interesting construction and operational principles, decorative natures, and low-cost production. To develop high-performance DSSCs, an epoch-making molecular design toward creating efficient dye sensitizers is required. For this purpose, we have designed and synthesized a new-type of D-π-A dye sensitizers with azine ring such as pyridine, pyrazine, triazine and pyridinium ring, as electron-withdrawing anchoring group. Our work revealed that D-π-A dye sensitizers with azine rings can adsorb onto TiO₂ surface through the formation of hydrogen bonding, azinium ion or coordination bonding at Brønsted acid sites or the Lewis acid site of TiO₂ surface, leading to efficient electron injection from the dye to the conduction band of TiO₂ electrode. Consequently, we propose that the azine ring capable of binding with both Brønsted acid sites and the Lewis acid site of TiO₂ surface is one of the most promising of dye sensitizers for DSSCs.

This review describes the systematic study on the red light-emitting behavior of a series of donor-acceptor-type dyes containing a strong acceptor moiety such as benzothiadiazole, naphthobisthiadiazole, bisthiadiazoloquinoxaline, and hexaazatriphenylene. Donor-acceptor conjugation is one of the simplest strategies for generating longer-wavelength emissions including red light emission. With the increase in the strength of donor-acceptor conjugates, the emission band shifts bathochromically, producing red light emission. However, the efficiency of red light emission decreases to show the quenching in polar aqueous media, because a highly polarized excited state arising from the donor-acceptor characteristic increases the formation of a nonradiative deactivation channel. An efficient red light emission can be achieved in the aggregation of the donor-acceptor dyes even in polar aqueous media. The formed aggregate provides a less polar hydrophobic space inside the aggregate structure, by which the quenching is restricted, leading to the reduction of the nonradiative deactivation rate.

In this paper, the efficient methodology for the synthesis of multi-substituted olefins by using zirconocene complexes is described. The key step is regioselective formation of zirconacyclopentenes from alkynylboron and alkynylsilane compounds. The subsequent Negishi and Suzuki-Miyaura coupling reactions of C-B and C-Zr bonds give rise to multi-substituted olefins. The developed reaction can be applicable to the synthesis of various functional molecules, for example, an anti-cancer agent. In addition, the mechanism for a regioselective formation of zirconacyclopentenes is analyzed by reactions of alkynylboronates and a zirconocene(II) complex. As a result, it is disclosed that an electrostatic interaction effected the regioselective formation of zirconacyclopentenes. The synthesis of various unprecedented tri- and tetra-alkylated olefins using β-hydrogen-containing alkyl electrophiles and alkylzinc reagents as coupling partners in regio- and stereocontrolled manners is also described.

The diene-transmissive hetero-Diels-Alder reaction (DTHDA reaction) is a special case of the DTDA reaction in which one or more heteroatoms are contained within either a cross-conjugated triene/polyene (heterodendralene) π-system, a dienophile π-system or both. Therefore, the DTHDA protocol is an efficient and attractive method for the stereoselective synthesis of a variety of heterocyclic systems. Merits and potential of the DTHDA methodology for heterocyclic synthesis can be widely extended by structural variations and complexity of both diene and dienophile; the kind, numbers, and positions of heteroatoms contained in either the cross-conjugated triene/polyene ([3/n] heterodendralene) or the dienophile framework, as well as the inter- or intramolecular cycloaddition mode, and its predictable regio- and stereoselectivities. In this paper, we introduce the synthesis of a variety of heterocycles using the DTHDA reaction with a focus on our research.

We developed various metalloporphyrins as bifunctional catalysts for the synthesis of cyclic carbonates from epoxides and CO₂ under solvent-free conditions. The structures of the bifunctional catalysts were optimized step by step. As a result, a Zn porphyrin bearing eight nucleophiles at the meta positions showed a high turnover number (TON=240,000) at 120 °C at 1.7 MPa CO₂ and catalyzed the reaction even at atmospheric CO₂ pressure (balloon) at ambient temperature (20 °C). Triporphyrin catalysts showed very high catalytic activity: TON=220,000 and TOF=46,000 h^-1 for the Mg triporphyrin, and TON=310,000 and TOF=40,000 h^-1 for the Zn triporphyrin. The high catalytic activity of these bifunctional catalysts was due to the cooperative action of Mg²⁺ or Zn²⁺ and Br^- and a conformational change (induced-fit) of the quaternary ammonium cation.

Acyl metal species generated from carboxylic acid derivatives upon treating with low valent transition-metal complexes have been utilized for various catalytic transformations. Recently, it was revealed that a catalyst system of Ni(0)/NHC(N-Heterocyclic Carbene) triggered amide C-N bond cleavage via oxidative addition to afford acyl nickel complexes. The obtained acyl species were further converted into the corresponding esters and ketones in catalytic manner. A proposed reaction mechanism and some synthetic applications are concisely summarized herein.

With a strong desire to develop radical carbonylation chemistry, we naturally focused our attention on the key reactive intermediate, the acyl radical. Acyl radicals have been regarded as nucleophilic radicals towards electron-poor alkenes, akin to vinyl radicals. However, deeming that acyl radicals may act as pseudo-carbonyl compounds, we observed acyl radicals to behave as electrophilic species, very unlike vinyl radicals. This essay is a personal account of the area of acyl radical chemistry.