Tomoaki Hinoue

Regulation of π‐Stacked Anthracene Arrangement for Fluorescence Modulation of Organic Solid from Monomer to Excited Oligomer Emission

The construction and precise control of the face-to-face π-stacked arrangements of anthracene fluorophores in the crystalline state led to a remarkable red shift in the fluorescence spectrum due to unprecedented excited oligomer formation. The arrangements were regulated by using organic salts including anthracene-1,5-disulfonic acid (1,5-ADS) and a variety of aliphatic amines. Because of the smaller number of hydrogen atoms at the edge positions and the steric effect of the sulfonate groups, 1,5-ADS should prefer face-to-face π-stacked arrangements over the usual edge-to-face herringbone arrangement. Indeed, as the alkyl substituents were lengthened, the organic salts altered their anthracene arrangement to give two-dimensional (2D) edge-to-face and end-to-face herringbone arrangements, one-dimensional (1D) face-to-face zigzag and slipped stacking arrangements, a lateral 1D face-to-face arrangement like part of a brick wall, and a discrete monomer arrangement. The monomer arrangement behaved as a dilute solution even in the close-packed solid state to emit deep blue light. The 1D face-to-face zigzag and slipped stacking of the anthracene fluorophores caused a red shift of 30-40 nm in the fluorescence emission with respect to the discrete arrangement, probably owing to ground-state associations. On the other hand, the 2D end-to-face stacking induced a larger red shift of 60 nm, which is attributed to the excimer fluorescence. Surprisingly, the brick-like lateral face-to-face arrangement afforded a remarkable red shift of 150 nm to give yellow fluorescence. This anomalous red shift is probably due to excited oligomer formation in such a lateral 1D arrangement according to the long fluorescence lifetime and little shift in the excitation spectrum. The regulation of the π-stacked arrangement of anthracene fluorophores enabled the wide modulation of the fluorescence and a detailed investigation of the relationships between the photophysical properties and the arrangements.

Systematic investigation of molecular arrangements and solid-state fluorescence properties on salts of anthracene-2,6-disulfonic acid with aliphatic primary amines.

Organic salts of anthracene-2,6-disulfonic acid (ADS) with a wide variety of primary amines have been fabricated, and their arrangements of anthracene molecules and solid-state fluorescence properties investigated. Single-crystal X-ray studies reveal that the salts show seven types of crystal forms and corresponding molecular arrangements of anthracene moieties depending on the amine, while anthracene shows only one form and arrangement in the solid state. Depending on the molecular arrangements, the ADS salts exhibit various solid-state fluorescence properties: spectral shift (30 nm) and suppression and enhancement of the fluorescence intensity. Especially the ADS salt with n-heptylamine (nHepA), which shows discrete anthracene moieties in the crystal, exhibits the highest quantum yield (Phi(F)=46.1+/-0.2%) in the series of ADS salts, which exceeds that of anthracene crystal (Phi(F)=42.9+/-0.2%). From these systematic investigations on the arrangements and the solid-state properties, the following factors are essential for high fluorescence quantum yield in the solid state: prevention of contact between pi planes of anthracene moieties and immobilization of anthracene rings. In addition, such organic salts have potential as a system for modulating the molecular arrangements of fluorophores and the concomitant solid-state properties. Thus, systematic investigation of this system constructs a library of arrangements and properties, and the library leads to remarkable strategies for the development of organic solid materials.

Chiral Recognition and Kinetic Resolution of Aromatic Amines via Supramolecular Chiral Nanocapsules in Nonpolar Solvents

Herein we report the first example of chiral recognition and kinetic resolution of aromatic amine guests using supramolecular nanocapsules assembled from cyclodextrin derivatives in nonpolar media. With these nanocapsules, an extremely high chiral recognition of 1-(1-naphthyl)ethylamine (1) in cyclohexane was achieved, with a binding selectivity of up to 41 for (S)-1 over (R)-1. In addition, kinetic resolution of 1 through enantioselective N-acylation was accomplished with an enantiomeric excess of up to 91%.

Guest-Responsive Fluorescence of Inclusion Crystals with π-Stacked Supramolecular Beads†

Lattice inclusion host compounds entrap guest molecules of various sizes into their flexible cavities formed by the host framework. The inclusion phenomena have been extensively investigated because of the potential application of these compounds in many fields such as separation, storage, catalysis, and chemical sensing. Considerable efforts have demonstrated that bulky and rigid molecules, or awkwardly shaped molecules, tend to include guest molecules because they do not pack easily without guests. For example, crystals of anthracene derivatives bearing diphenylphosphanyl groups at the 9and 10-positions include toluene molecules and show on/off fluorescence switching by absorption and desorption of the guest. Inclusion of various guests into fluorescent hosts will afford a multitude of fluorescent colors as if doping strongly affects the colors of jewels, as seen in sapphires and rubies. However, chemical affinity of their inclusion spaces often limits the appropriate guest molecules (i.e. polar or nonpolar molecules). Therefore, it still remains challenging to design new lattice host compounds that efficiently incorporate and respond to a wide range of guests. Previously, we readily prepared bulky and rigid supermolecules from simple molecules: triphenylmethylamine (TPMA) and a variety of sulfonic acids. Four TPMA molecules and four monosulfonic acid molecules formed cubic hydrogen-bonding (H-bonding) networks completely covered with their substituents (Figure 1a). Herein, in order to create fluorescent materials responsive to various guests, we have designed a new host supermolecule that possesses two aromatic fluorophores at the periphery. The fluorescent host forms one-dimensional (1D) p-stacked

Iridium‐Catalyzed Aerobic Coupling of Salicylaldehydes with Alkynes: A Remarkable Switch of Oxacyclic Product

The iridium(III)/copper(II)-catalyzed dehydrogenative coupling of salicylaldehydes with internal alkynes proceeds efficiently under atmospheric oxygen through aldehyde C-H bond cleavage and decarbonylation. A variety of benzofuran derivatives can be synthesized by the environmentally benign procedure. DFT calculations suggest that this unique transformation involves the facile deinsertion of CO in the key metallacycle intermediate, which is in marked contrast to the corresponding rhodium(III) catalysis that leads to CO-retentive chromone derivatives.

Drastic modulation of solid-state luminescence derived from molecular arrangement of organic salts

Polycyclic p-conjugated molecules, such as anthracene and pyrene, are employed in many systems owing to their electroand photophysical properties. Their properties in solid state depend not only on the molecular structure but on the molecular arrangements. As for the photoluminescent properties, there are several reports on the relationships with molecular arrangements. However, the relationships have not been elucidated exactly and therefore further study is necessary for the application to the development of sophisticated organic devices. Here, we present drastic modulation of luminescent color triggered by change of the anthracene arrangement of ammonium anthracene-1,8-disulfonate. The organic salts gave seven kinds of anthracene arrangements depending on the amine of the salts. Alkyl chain of n-butylamine surround anthracene moieties, resulting in blue luminescence attributed to monomer emission. Whereas, s-butylamine afforded formation of dimer pairs and contact of the pairs, resulting in orange luminescence attributed to excimer emission. Up to 150 nm of red shift depending on anthracene arrangements was achieved.