Bioluminescent systems have received a great attention due to their unique capability to monitor biological components, such as ATP, Ca²⁺ ion, and reactive oxygen species (ROS), by emitting light. Coelenterazine (CL) is the organic substance for the chromophore of aequorin, which emits blue light in the presence of Ca²⁺ ion. Dehydrocoelenterazine (DCL) is the organic substance for bioluminescence of symplectin and pholasin that emit light in the presence of ROS. DCL is prepared by oxidation of CL, and a synthetic route for CL had already established more than 50 years ago. Condensation of coelenteramine and α-ketoaldehyde affords CL, which has imidazo[1,2-a]pyrazine-3(7H)-one core structure. However, the synthetic route is not efficient when many varieties of CL or DCL analogs are required. Therefore, many researchers have paid their efforts in order to obtain those analogs. Cross-coupling reaction is the most powerful method for functionalizing of 2-aminopyrazines into coelenteramine analogs, which are important components for the synthesis of CL analogs. This review describes the synthesis of CL and DCL, and alternative methods for synthesis of their analogs.

Self-assembly of metalated amino acids and peptides enabled us to construct dimensionally- and hierarchically-controlled supramolecular organometallic compounds, being expected to exhibit unprecedented properties induced by synergistic interactions of multiply-arrayed metal complexes. We have developed several types of metalated amino acids, in which various functional transition-metal complexes are covalently conjugated to their α-side chains. Using the metalated amino acids as a metal-sequence-unit, programed sequence of metal complexes can be achieved through peptide synthesis to afford multi-metalated peptides. Higher ordered structures was successfully constructed by self-assembling the metalated amino acids and peptides to provide well-defined supramolecular architectures. The supramolecular aggregates of metalated amino acids and peptides have been applied to both homogeneous and heterogeneous catalytic organic reactions to explore their potential utilities.

Mechanofluorochromic dyes can exhibit a change in fluorescent colour by external mechanical stimuli to the solids, being accompanied by a reversion to the original fluorescent color by heating or exposure to solvent vapor, which have attracted much attention from chemists, physicists, and engineers because of enormous scientific interest in the fundamental research fields of photochemistry and photophysics and interesting smart materials for next generation optoelectronic devices. We have found that newly developed heteropolycyclic donor-acceptor π-conjugated (D-π-A) fluorescent dyes with electron-withdrawing substituents as acceptor show a bathochromic shift-type mechanofluorochromism (MFC). Our work revealed that the MFC of D-π-A fluorescent dyes is attributed to a reversible switching between crystalline and amorphous states with changes of dipole-dipole interaction and intermolecular π-π interaction. We propose that the most important point for developing MFC dyes is to design D-π-A fluorescent dye molecules with moderate dipole moments (ca. 5 Debye) which are controlled by tuning the electron-donating ability of D, electron-accepting ability of A, steric size of a substituent, and D-π-A system. On the other hand, we demonstrated that the bathochromic shift-type MFC of unsymmetrical carbazole-type D-π-A fluorescent dyes is attributed to a reversible switching between crystalline and amorphous states with changes of intermolecular hydrogen bonding and π-π interaction. We also propose that the use of various counter anions for D-π-A pyridinium dyes can be one of the most effective strategies, not only to express a pronounced MFC, but also to control changes of fluorescence properties by the grinding and heating, resulting in fine-tuning of fluorescent color change by the MFC.

In recent years, luminescent organic compounds including group 13—16 elements have been extensively studied from the viewpoints of applications for electronic devices and chemical sensors, in which the group 13—16 elements play an important role by providing a perturbation to the photophysical property of original hydrocarbons. We have developed dibenzobarrelene-incorporated 1-chalcogeno-1,3-butaidiene derivatives being fluorescent with high efficiency, which are synthesized by two methods; (1) the reaction of thio- or selenometallacycles with dimethyl acetylenedicarboxylate or (2) the intramolecular cycloaddition between (9-anthryl)chalcogeno and arylalkynyl groups connected by a (Z)-alkenyl group. The latter method (2) are applied to the syntheses of benzobarrelene analogues, 1-aza-1,3-butadiene analogues by cyano-Diels-Alder reaction, thiophene-fused analogues, and derivatives having π-donor and π-acceptor substituents that luminesce in the near-infrared region. In addition, we have succeeded in the synthesis of carbon and silicon analogues utilizing the intramolecular cycloaddition. In this paper, we describe the syntheses of the luminescent compounds in details with comparing their relevant and characteristic photophysical properties.

We have focused on planar chirality of [2.2]paracyclophanes with substituent(s). In addition, we have developed their practical optical resolution methods by mainly diastereomer methods and synthetic routes to planar chiral [2.2]paracyclophane compounds. The obtained optically active disubstituted and tetrasubstituted [2.2]paracyclophanes have been utilized for chiral building blocks to produce a wide variety of optically active π-stacked molecules including polymers. The planar chiral [2.2]paracyclophane-based π-stacked molecules exhibited circularly polarized luminescence (CPL) with a large dissymmetry factor (g_lum value) derived from the optically active second-ordered structures, such as V-, X-, triangle-, one-handed double helical structures, in the excited state. It was the first example on the application of the planar chirality of [2.2]paracyclophane to the field of polymer chemistry as well as materials chemistry. π-Electron systems constructed by [2.2]paracyclophane emit photoluminescence (PL) depending on the conjugation length of the stacked π-electron system. When conjugation length of a stacked π-electron system is extended, the molecule exhibits monomeric PL rather than excimer-like PL despite the stacked structure in proximity. Even if the several tens of π-electron systems are stacked, PL profiles such as PL life time and quantum efficiency are identical. π-Conjugation lengths of monomeric π-electron systems in this article are sufficiently extended; thus, the [2.2]paracyclophane-based π-stacked molecules in this article emit brightly with good PL quantum efficiencies. Moreover, the luminescence is CPL with the large g_lum value in organic molecules. It is quite difficult to achieve CPL with high brightness, high PL efficiency, and large g_lum value by using other scaffolds; therefore, planar chiral [2.2]paracyclophane is the ideal scaffold to be an excellent CPL emitters.

Aminobenzopyranoxanthene (ABPX) dye, developed by our group, exhibits two-step color change in solution through a spiro-ring opening/closing process in response to chemical stimuli such as acids, metal ions and phenols. Using this unique characteristic, we have developed ABPX-based colorimetric sensor that change color depending on Cu²⁺ concentration, enabling visualization by spectrophotometry and the naked eye. Furthermore, an efficient and practical method to prepare ABPX with various nitrogen-containing fused rings was developed. Using a simple acid-catalyzed reaction consisting of 1,3-diisopropoxybenzene and CH₃SO₃H, a variety of benzophenones gave ABPX directly in excellent yields. We discovered that ABPX is a new type of mechanochromic organic molecule with a large wavelength difference of fluorescence (near-IR/blue). Detailed spectrophotometric and single-crystal X-ray analyses revealed that the near-IR fluorescence is attributable to fluorescence from slip-stacked dimeric structures in crystals, while the blue fluorescence is attributable to fluorescence from the monomer. Switching between the two is achieved by dynamic structural interconversion in response to mechanical grinding and exposure to the vapor of solvents.

High-birefringence liquid crystal materials are used in a wide variety of optical applications such as reflection films and photo storage devices; they are likely to find more applications with increasing research in this area. The design concept is an essential aspect of high-birefringence liquid crystals. We investigated the structure-optical property relationship (liquid crystallinity, refractive index and birefringence) of rod-like mesogens from the viewpoint of physical organic chemistry. We first investigated how the acetylene bond affects nematic transition behavior and refractive index parameters of the conjugated oligoyne or polyyne compounds with two terminal aromatic rings in each single component medium. We synthesized novel, highly birefringent nematic liquid crystal materials: 1,6-diphenyl-1,3,5-hexatriyne derivatives with various alkoxy chains. The derivatives exhibit stable enantiotropic nematic phases. We revealed that a higher number of acetylene units (from 1 to 3), i.e., extended conjugation, led to wider temperature range nematic phases and higher birefringence. The increment in Δn per acetylene unit was estimated to be 0.14. We then studied the use of heteroatoms with high atomic refraction. Sulfur-containing rod-like materials usually have high birefringence values but do not exhibit enantiotropic mesophases because they tend to crystallize or show mesophase instability. We incorporated carboxylic acid end groups into thioether-containing diphenyl-acetylene-based compounds, our hypothesis being that the acid groups would impart mesophase stability through hydrogen-bond driven dimerization. These compounds exhibited highly correlated long-range mesophases and high birefringence compared with their alkyl and alkoxy analogues. We also developed a new and simple process to prepare phenolic-hydroxyl-group substituted diphenyl-acetylene and diphenyl-diyne derivatives. Using these molecules, we prepared transparent and colorless high-birefringence polymer films. Our studies show that this review could be a guide for the design of high-birefringence liquid crystal materials.

To date, the development of easy-to-use chemical sensors has become increasingly important in the field of healthcare applications or environmental assessments. Toward that end, organic thin-film transistors are some of more intriguing devices owing to solution-processability, mechanical flexibility, durability, easy miniaturization, low-fabrication-costs, etc. In this regard, we herein report chemical sensors on the basis of organic thin-film transistors (OTFTs) functionalized with artificial receptors. One of our developed sensors is an extended-gate type OTFT, which means that the molecular (or ion) recognition site of the OTFT is a partially extended gate electrode. Self-assembled monolayers with artificial receptors were fixed on the surface of the electrode. Such a fabricated OTFT has been successfully applied to the electrical detection of heavy metal cations (ex. Cu²⁺) or small inorganic anions (ex. F^-) in aqueous solutions, which could thus contribute to easy-to-use environmental monitor kits. The other type of our fabricated sensor is an electrolyte-gated type OTFT. A chemical-stimuli responsive polythiophene pendant with a carboxy side-chain which enables us to achieve the detection of biogenic amines (ex. histamine) in water. Importantly, the fabricated sensors are reusable, because the molecular recognition is derived from reversible interactions such as metal-ligand coordination, hydrogen-bonding and/or electrostatic interaction, etc. We believe that the combination of OTFTs and artificially synthesized receptors can open up a new research field such as supramolecular analytical devices.

The oxidative coupling reaction of boronic acids or boronic esters by using palladium nano particle/palladium colloid under mild condition was reported. Various boronic acids were available and highly strained macrocyclic compounds were also synthesized.

Small-membered phosphacycles are found to mimic catalytic reactivities of transition metals by adopting P^III/P^V redox cycles or Phosphorus-Ligand cooperation. Structural constraint on the phosphorous center perturbs various properties including Lewis acidity, s-character of the lone pair and inversion barrier at the phosphorous center, which realizes unusual phosphorous-based catalysts. This review summarizes recent works on transition metal-like behaviors of three-coordinate phosphorous compounds reported by Radosevich's group.

The compound libraries visualized by organic chemists do not conform with those by biologists. Biologists prefer libraries that contain diverse “drug-like” compounds. In this article, we have introduced a method for constructing compound libraries with drug-likeness and diversity by utilizing “drug-likeness indexes”. The indexes are useful for the quantification of structural features of compounds and for the design of diverse-orientated libraries. In addition, we characterized natural products through the use of drug-likeness indexes, and described the usage of those for library constructions.