Bathochromic Shift of Fluorescence Peak in Dipyrrolo[1,2-a:2',1'-c]quinoxaline by Introducing Each of Electron-Donating and Electron-Withdrawing Substituent.

Development of organic fluorophore is an important theme. Especially, the fluorophores with longer fluorescence peaks are useful to biological probes. One of the methods to change the fluorescence peak is the introduction of substituents. However, opposing characteristics of the substituents lead to different changes in the fluorescence peaks. Furthermore, the introduction of the substituent also affects their electric properties. Thus, if the materials were developed with the substituent effect on the optical and electric properties separately, it will be useful to design the functional materials related to both optical and electric properties. Herein, we investigated the substituent effect of dipyrrolo[1,2-a:2',1'-c]quinoxalines on fluorescence properties. We synthesized the compounds bearing electron-donating or electron-withdrawing substituents at the benzene ring on dipyrrolo[1,2-a:2',1'-c]quinoxaline, which would have more direct influence on the optical properties. By introducing each substituent at the 6 position of dipyrrolo[1,2-a:2',1'-c]quinoxaline, the bathochromic shift was observed in the fluorescence spectra. In the case of fluorine substituent, the change of the fluorescence peak reached was about 19 nm. Using a TDDFT calculation, we explained the reason for such a substituent effect that large on the increment of LUMO energy or decrement of HOMO energy occurred by introducing electron-withdrawing or electron-donating substituents at the 6 position, respectively. The substituent effect on the change of orbital energies is typical although the different characteristics of substituents resulted in the similar tendency about the change of fluorescence peak. Furthermore, with the introduction of phenyl substituents at the 3 and 10 positions, we achieved 40-50 nm longer fluorescence peaks compared with that of the original dipyrrolo[1,2-a:2',1'-c]quinoxaline.

Incrementing Stokes Shifts through the Formation of 2,2'-Biimidazoldiium Salts.

The formation of biimidazoldiium structures by the introduction of methyl substituents on the N atoms at the 3 and 3' positions of 2,2'-biimidazoles led to increments in the Stokes shift of these structures. Based on time-dependent density functional theory (TDDFT) calculations, the imidazolium rings become distorted and the N atoms of the imidazolium rings underwent structural changes through sp2 to sp3 rehybridization in the excited states.

Selective Formation of Internal Olefinic Trimer of α-Methylstyrenes with HI Gas and Ketones.

Reaction of α-methylstyrene in the presence of HI gas and methyl p-tolyl ketone selectively resulted in an internal olefinic trimer. We revealed that the ketones with the stabilization of the protonated state were efficient to give the corresponding trimers, whereas the other ketones gave the usual indane compound. From the investigation for the mechanistic path, we found that the trimer is a kinetic product and that indane is a thermodynamic product.

Preparation of chiral 3-oxocycloalkanecarbonitrile and its derivatives by crystallization-induced diastereomer transformation of ketals with chiral 1,2-diphenylethane-1,2-diol.

Chiral 3-oxocycloalkanecarbonitriles were prepared by fractional crystallization and crystallization-induced diastereomer transformation (CIDT) of diastereomeric ketals with (1R,2R)-1,2-diphenylethane-1,2-diol. Investigation of the crystal structures by X-ray diffraction analysis revealed that the difference in hydrogen bonds caused the discrepancy of the solubilities between (R) and (S) diastereomers. Furthermore, CIDT to afford the (R)-diastereomer in good yield (95% yield) and with high diastereoselectivity (97% de) was accomplished, which is the first example of CIDT of neutral compounds via formation of the diastereomeric ketal with (1R,2R)-1,2-diphenylethane-1,2-diol.

Formation of Benzimidazoisoquinolinium and Benzimidazoisoindolinum Cyclic Systems by the Reaction of 2-(2-Alkynylphenyl)benzimidazoles with Iodine and Iodine-Iodine Interaction Including Halogen Bonding in Their Crystal Structures.

The reaction of 2-(2-alkynylphenyl)benz[d]imidazoles with molecular iodine constructed 5- and 6-membered rings as novel organic salts in high yield. The constituted number of ring systems was influenced by the substituent at the triple bond: 6-membered rings were formed from compounds bearing aryl substituents, whereas 5-membered ones were obtained from compounds with hydrogen or alkyl substituents. The products were obtained with triiodide as a counteranion; however, compounds with iodide were also obtainable under certain conditions. We also revealed that they had an iodine-iodine interaction included in halogen bonding between an iodo moiety of the cation and a triiodide or iodide of the counteranion. The iodine-iodine interaction was formed with greater preference than the electrostatic interaction between the cationic atom and triiodide or iodide.

CH/π Interactions for Macroscopic Interfacial Adhesion Design.

Adhesion to chemically inert materials without surface modification through noncovalent interactions represents a challenging task in adhesion science. We successfully develop for the first time a strategy utilizing multiple CH/π interactions that use poly(methacrylate) with an aromatic group (H acceptor) in the ester part and polyolefin materials (H donor). The strength increases with the number of π electrons and aromatic rings. The trityl methacrylate polymer emerges as the most effective H-acceptor polymer for obtaining strong adhesion to various polyolefin materials. This work will provide not only a promising adhesion strategy that does not require surface activation for polyolefin materials, but also a novel approach using weak noncovalent interactions.

Fluorescence of diimidazo[1,2-a:2',1'-c]quinoxalinium salts under various conditions.

The synthesis and photophysical properties of diimidazo[1,2-a:2',1'-c]quinoxalinium salts were examined for different counteranions. The ethyl-substituted diimidazo[1,2-a:2',1'-c]quinoxalinium salt with tosylate anion (categolized in ionic liquid) showed good fluorescence (ΦF = 0.77) in organic solvent. The 3,10-diphenyldiimidazo[1,2-a:2',1'-c]quinoxalinium salts showed absorption and fluorescence peaks resembling those of the former diimidazoquinoxaline. The salt also emitted under various conditions such as in organic solvents, water, and even in the solid state, while retaining a good fluorescence quantum yield (ΦF = 0.5-0.8). Furthermore, the fluorescence was quenched efficiently through the introduction of an electron-donating substituent on the alkyl side chain.

α-Diketone formation accompanied by oxidation of sulfur functional group by the reaction of o-alkynylarenesulfoxide with iodine.

The reaction of o-alkynylarenesulfoxide with iodine was investigated in detail, revealing functionalities of the formation of α-diketones with sulfenyl, sulfinyl, and sulfonyl. Additives can change the ratio of products to give medium-to-excellent yields. Results show that water is taken into only sulfonyl compound and that other oxygen atoms constructed in the products are presumably derived from sulfoxide of the starting material and molecular oxygen.

Novel formation of diimidazo[1,2-a:2',1'-c]quinoxaline derivatives and their optical properties.

Reaction of 1,2-di(imidazolyl)benzene treated with n-BuLi proceeded to give diimidazo[1,2-a:2',1'-c]quinoxaline in the presence of iodine or Pd(PPh(3))(4). Blue fluorescence was observed from 3,10-diarylated diimidazoquinoxalines with high quantum yield. They were also applied to organic light-emitting devices as emitters, in which the diphenyl derivative emits a nearly pure blue light.

Synthesis and C(2) -symmetric structure of a cyclotetrapeptide composed of anthranilic acid and leucine.

A chiral cyclotetrapeptide (1) was synthesized from 2-nitrobenzoic acid and leucine. A single-crystal X-ray of the compound revealed a C(2) -symmetric bowl-shaped structure. The cyclic compound had a unique hydrogen-bonding network composed of three-centered hydrogen bonds and bifurcated hydrogen bonds between NH and CO of anthranilic residue. The NMR spectra and molecular modeling of 1 also suggested the chiral bowl structure.

Predominant (S)-enantioselective inclusion of aryl methyl sulfoxides by (S)-isoleucyl-(S)-phenylglycines.

In terms of chiral recognition for racemic aryl methyl sulfoxides in the solid state, three kinds of crystalline (S)-alkylglycyl-(S)-phenylglycines were examined as potential dipeptides host molecules. When (S)-alanyl-(S)-phenylglycines [(S,S)-Ala-Phg] crystallized with aryl methyl sulfoxides, the stereochemistry of preferentially included sulfoxides depended on the individual shapes of the sulfoxides and the enantiomeric excess was relatively low. Although (S)-leucyl-(S)-phenylglycines [(S,S)-Leu-Phg] and (S)-isoleucyl-(S)-phenylglycines [(S,S)-Ile-Phg] mainly included the S-form of aryl methyl sulfoxides, the enantiomeric recognition of (S,S)-Ile-Phg was superior to that of (S,S)-Leu-Phg. Single-crystal X-ray analysis of these inclusion compounds revealed that the dipeptide molecules self-assembled to form layer structures and included sulfoxides between these layers through hydrogen bonding between the proton of (+)NH(3) and the oxygen of the sulfoxide. Besides these host-guest interactions, the phenyl groups of the sulfoxides interacted with each other through the phenyl-phenyl interaction. Two adjacent homochiral sulfoxides make a pair having a 2-fold screw axis along the channel cavity. Thus, the self-recognition of sulfoxides made 2(1) helical column structures and had high enantioselectivity.

Novel synthesis of alpha-trifluoromethylated alpha-amino acid derivatives from gamma-hydroxy-alpha-fluoro-alpha-trifluoromethyl carboxamides.

On treatment with an organoaluminum reagent such as trimethylaluminum or DIBAL-H, gamma-hydroxy-alpha-fluoro-alpha-trifluoromethyl carboxamides (1) give a single diastereomer of alpha-amino-alpha-trifluoromethyl-gamma-lactones (2), which are a ring-closed form of gamma-hydroxy-alpha-trifluoromethyl-alpha-amino acids. This intriguing reaction results from intramolecular replacement of the fluorine atom on the alpha-carbon atom with the nitrogen atom of the amide group, which occurs in an SN2 manner. [reaction: see text]

Formation of gold-like metal-lustrous inclusion crystals from 1-phenyl-2,5-bis[5-(tricyanoethenyl)-2-thienyl]pyrrole host and an electron-donating aromatic guest.

A novel pi-conjugated organic compound, 1-phenyl-2,5-bis[5-(tricyanoethenyl)-2-thienyl]pyrrole, which bears two powerful electron-withdrawing tricyanoethenyl substitutents, readily yielded gold-like metal-lustrous inclusion crystals with a series of aromatic guest molecules such as toluene, p-xylene, anisole, dimethoxybenzenes and indene. All the inclusion compounds have a common stoichiometric ratio (host/guest) of 2 : 1. X-Ray structural analyses demonstrate that the structural feature for toluene included crystal is similar to those containing p-xylene, anisole, dimethoxybenzenes and indene.

Sheet structure of an L,D-dipeptide aggregate: inclusion compounds of (S)-phenylglycyl-(R)-phenylglycine with amides.

A simple dipeptide, (S)-phenylglycyl-(R)-phenylglycine (S,R-1), formed inclusion compounds with a small amide such as formamide, acetamide, N,N-dimethylformamide (DMF), or N,N-dimethylacetamide. By single-crystal X-ray analysis, the inclusion compounds were shown to have a wavy layer structure. The molecules of S,R-1 are arranged in parallel via ionic pairing of the carboxyl and amino groups to construct the wavy layers. The guest molecules were accommodated in a channel cavity between the layers by means of hydrogen bonding with (+)NH(3) of S,R-1. The cavity is surrounded by the phenyl groups of S,R-1 that conformationally rotate so as to make the cavity size fit the guest amide.