Chromic properties of dibenzo[j,l]fluoranthenes exhibiting different resonance contributions.

Chromic molecules change colour in response to external stimuli and are utilized in applications such as food additive detection, light dimmers, and biological probes. One of the common design strategies for organic chromic molecules is based on changes in the π-conjugation. We have hypothesized that non-alternant polyaromatic hydrocarbon (PAH) skeletons can be used as backbones for chromic molecules. Herein, we synthesized hydroxy-substituted dibenzo[j,l]fluoranthenes, a class of non-alternant PAHs, as novel chromic compounds and evaluated their halochromic properties by UV-vis and fluorescence spectroscopy. Under basic conditions, the 1-hydroxy derivatives show a hyperchromic shift, whereas the 9-hydroxy derivatives show a bathochromic shift and fluorescence although the skeleton of the chromophore is the same. Density functional theory calculations indicated that the different chromic properties are attributed to the differences in their resonance structures.

Synthesis and Optical Properties of Binaphthyl Derivatives with Comprehensive Introduction of Phenylethynyl Groups.

In this study, compounds with phenylethynyl (PE) groups introduced at all of the possible positions of the methylene-bridged structure of the 1,1'-bi-2-naphthol backbone (3-PE to 8-PE) were synthesized. Compounds with four or six phenylethynyl groups (3,6-PE, 4,6-PE, 5,6-PE, 6,7-PE, and 3,4,6-PE) were also synthesized. The key reaction for the synthesis of these compounds was the Sonogashira reaction using halogen scaffolds. The new transformation methods include (1) selective bromination of the 5-position of the binaphthyl skeleton and (2) bromination of the 6-position and then iodination of the 4-position, followed by the Sonogashira reaction of iodine at the 4-position and lithiation and protonation of bromine at the 6-position. The optical properties of the compounds were evaluated. The extension of the π system greatly differed depending on the position of the phenylethynyl group. 4-PE, 4,6-PE, and 3,4,6-PE, in which the phenylethynyl groups were introduced in the extended direction of the naphthalene linkage axis, showed longer absorption and emission wavelengths and higher fluorescence quantum yields than the other compounds. In circularly polarized luminescence measurements, 7-PE showed a relatively large glum value, an interesting finding that reverses the sense.

Aggregation-induced enhanced fluorescence emission of chiral Zn(II) complexes coordinated by Schiff-base type binaphthyl ligands.

A pair of novel chiral Zn(II) complexes coordinated by Schiff-base type ligands derived from BINOL (1,1'-bi-2-naphthol), R-/S-Zn, were synthesized. X-ray crystallography revealed the presence of two crystallographically independent complexes; one has a distorted trigonal-bipyramidal structure coordinated by two binaphthyl ligands and one disordered methanol molecule (molecule A), while the other has a distorted tetrahedral structure coordinated by two binaphthyl ligands (molecule B). Numerous CH⋯π and CH⋯O interactions were identified, contributing to the formation of a 3-dimensional rigid network structure. Both R-/S-Zn exhibited fluorescence in both CH2Cl2 solutions and powder samples, with the photoluminescence quantum yields (PLQYs) of powder samples being twice as large as those in solutions, indicating aggregation-induced enhanced emission (AIEE). The AIEE properties were attributed to the restraint of the molecular motion arising from the 3-dimensional intermolecular interactions. CD and CPL spectra were observed for R-/S-Zn in both solutions and powders. The dissymmetry factors, gabs and gCPL values, were within the order of 10-3 to 10-4 magnitudes, comparable to those reported for chiral Zn(II) complexes in previous studies.

Aggregation-induced circularly polarized phosphorescence of Pt(II) complexes with an axially chiral BINOL ligand.

A pair of chiral Pt(II) complexes coordinated by simple BINOL and bipyridine ligands displaying aggregation-induced phosphorescence and circularly polarized luminescence were characterized by X-ray crystallography and absorption and emission spectroscopies. The emission of the powder sample was reddish whereas the thin film dispersed in PMMA (fPf = 1 wt%) exhibited a white emission.

Multiply Twisted Chiral Macrocycles Clamped by Tethered Binaphthyls Exhibiting High Circularly Polarized Luminescence Brightness.

Invited for the cover of this issue are Masashi Hasegawa and co-workers at Kitasto University and Kyoto Prefectural University. The image depicts the reported multiply twisted chiral macrocycles as objects in a kaleidoscope. Read the full text of the article at 10.1002/chem.202202218.

Multiply Twisted Chiral Macrocycles Clamped by Tethered Binaphthyls Exhibiting High Circularly Polarized Luminescence Brightness.

Chiral macrocyclic dimers, trimers, and tetramers composed of paraphenylene and tethered binaphthyl were synthesized, and their molecular structures and chiroptical properties were investigated. X-ray analysis and theoretical calculations revealed that multiple twisted molecular structures - dimers, trimers, and tetramers - adopt figure-of-eight, Möbius triangle, and concave rectangle structures, respectively. These homologues have large ϵ values in their UV-vis absorption spectra because of the π-conjugation of the naphthalene-phenylene-naphthalene frameworks. Owing to the shape-persistent ring structure and tethering with -OCH2 CH2 O-, high fluorescence quantum yields and a relatively high dissymmetry factor gCPL in circularly polarized luminescence (CPL) spectra were achieved. This results in CPL brightness (BCPL ) of over 100, which is greater than that of the conventional organic CPL dye.

Synthesis and Properties of V-Shaped Xanthene Dyes with Tunable and Predictable Absorption and Emission Wavelengths.

V-shaped xanthene dyes capable of predicting absorption and emission wavelengths are described. These dyes were synthesized by bridging a xanthene ring and an aryl moiety of fluorescein through ether covalent bonds. These dyes showed longer absorption and emission wavelengths than those of the parent fluorescein. Furthermore, substituents introduced on the aryl moiety mainly affected the lowest unoccupied molecular orbital energy level of the molecule. Therefore, the Hammett substituent constants could be used to predict the absorption and emission wavelengths of the compound.

Synthesis of Bridged Indigos and Their Thermoisomerization and Photoisomerization Behaviors.

Bridged indigos were synthesized by bridging the two nitrogen atoms in the indigo structure with a carbon chain, and their properties were carefully examined. These bridged indigos have intrinsic planar chirality, and the enantiomers were separated using chiral high-performance liquid chromatography. When the chiral bridged indigos were subjected to thermo- and photoisomerization, the corresponding (Z)-indigo was not observed at all, and racemization was observed. This phenomenon is caused by the low activation energy of inversion due to the 1.5 bond order of the double bond of the indigo skeleton and the large energy difference between the ground states of (E)-indigo and (Z)-indigo.

Total Syntheses of FR-901235, Auxarthrones A-D, and Lamellicolic Anhydride.

In our previous study, an unusual rearrangement reaction was discovered whereby dinaphthyl ketones with three hydroxy groups at restricted positions were transformed into a phenalenone ring and a benzene ring. Using the rearrangement as a key reaction, the first total syntheses of FR-901235 and auxarthrones A-D from an unstable triketone common intermediate are described. Furthermore, lamellicolic anhydride was synthesized from the triketone. This conversion is part of the putative biosynthetic pathway and was achieved experimentally for the first time.

Nucleophilic Addition Reaction with Dearomatization of Naphthalene Ring.

Various aromatic lactones have been synthesized and their regioselectivity (1,2-addition vs. 1,4- or 1,6-addition) investigated in reactions with organolithium species, particularly n-BuLi and sec-BuLi. The regioselectivity varied greatly depending on various factors, such as the bulkiness of both substrates and organolithium species, and types of solvent and cosolvent. In particular, 1,4-addition with dearomatization occurred preferentially using sec-BuLi as the nucleophile in tetrahydrofuran (THF) with hexamethylphosphoramide (HMPA) or N,N'-dimethylpropyleneurea (DMPU) as cosolvent. For sec-BuLi, the reaction was estimated to proceed through a single-electron transfer mechanism.

Synthetic and Biological Studies of Juglorubin and Related Naphthoquinones.

Juglorubin, juglorescein, and juglocombins A/B are naturally occurring naphthoquinone dimers isolated from Streptomyces sp. These dimers are proposed to be biogenetically derived from juglomycin C, a monomeric naphthoquinone isolated from the same Streptomyces sp. In this study, the dimerization of a juglomycin C derivative, a key step in the total syntheses of these natural products, was investigated. Juglorubin was synthesized from the minor product of the dimerization via the formation of the juglocombin A/B stereoisomers. A mechanism for the dimerization reaction as well as a plausible biosynthetic pathway to obtain juglorubin from juglomycin C are proposed. Furthermore, the antibacterial and cytotoxic activities of five synthetic compounds were evaluated. Among the compounds tested in this study, 1'-O-methyljuglocombin B dimethyl ester and juglomycin C exhibited antibacterial activity against Bacillus subtilis. 1'-O-Methyljuglocombin B dimethyl ester and juglomycin C showed cytotoxicity against human colon carcinoma HCT116 cells and human leukemia HL-60 cells. 1'-O-Methyljuglocombin B dimethyl ester exhibited cytotoxicity against human normal MRC-5 cells as strong as that against human cancer cells. In contrast, juglomycin C was less toxic against normal MRC-5 cells, indicating a significant selectivity toward cancer cells.

Unified Approach toward Syntheses of Juglomycins and Their Derivatives.

A unified and common intermediate strategy for syntheses of juglomycins and their derivatives is reported. The use of a 1,4-dimethoxynaphthalene derivative as a key intermediate enabled easy access to various juglomycin derivatives. In this study, juglomycins A-D, juglomycin C amide, khatmiamycin and its 4-epimer, and the structure proposed for juglomycin Z were synthesized from this intermediate. The absolute configuration of natural khatmiamycin has been established to be 3R,4R through our synthesis. Unfortunately, the spectroscopic data for synthetic juglomycin Z were not consistent with the data reported for the natural one, strongly suggesting a structural misassignment.

Synthesis, antibacterial and cytotoxic evaluation of flavipucine and its derivatives.

The antibacterial and cytotoxic activity of seven racemic lactams and both enantiomers of flavipucine were evaluated. Of the compounds tested in this study, flavipucine and phenylflavipucine displayed bactericidal activity against Bacillus subtilis. These results indicate that the pyridione epoxide moiety is a pharmacophore for antibacterial activity against B. subtilis. Flavipucine showed cytotoxic activity against several cancer cells. The cytotoxic activity of flavipucine against human leukemia HL-60 cells is as strong as that of SN-38, the active metabolite of irinotecan. In contrast, the cytotoxic activity of flavipucine against nonneoplastic HEK293 cells and human normal MRC-5 cells is weaker than that of SN-38. No significant differences in the biological activity of the racemates or enantiomers of flavipucine were observed.

Synthesis and Photochemical Properties of Axially Chiral Bis(dinaphthofuran).

Both enantiomers of axially chiral bis(dinaphthofuran) were prepared in only two steps from 1'-hydroxy-4'-methoxy-2,2'-binaphthalenyl-1,4-dione, followed by optical resolution via high-performance liquid chromatography (HPLC) using a chiral stationary phase (CSP). The absolute configurations were determined by comparison of experimental and calculated vibrational circular dichroism (VCD) spectra. Synthetic bis(dinaphthofuran) exhibited a broad and unstructured emission derived from an intramolecular excimer in both solution and solid state. The methylene bridge brings both chromophores close to each other and induces significant changes in the photophysical behavior. Chiral bis(dinaphthofuran) displayed a bathochromic shift in emission, as compared to the racemic mixture in the solid state. Furthermore, the compounds showed high circularly polarized luminescence (CPL) with a dissymmetry factor ( glum) of 10-3 at 405 nm upon excitation at 265 nm in a methanol solution. This compound serves as a model for the design and synthesis of organic materials having CPL activity.

Synthesis and Properties of Tribenzocarbazoles via an Acid-Promoted Retro (2+2)-Cycloaddition of Azapropellanes.

We describe herein the development of a new method to synthesize tribenzocarbazoles via an acid-promoted retro (2+2)-cycloaddition of azapropellanes, which were prepared by potassium hexamethyldisilazide (KHMDS)-promoted (2+2)-cycloaddition. The tribenzocarbazoles showed strong fluorescence both in solution and the solid state. The structural, electronic, and optical properties of the synthetic tribenzocarbazoles are also described.

Bioinspired Synthesis of Juglorubin from Juglomycin C.

In this paper, the synthesis of juglorubin, a natural red dye, from juglomycin C, a plausible biogenetic precursor, is reported. Sequential intermolecular and intramolecular Michael additions of juglomycin C, oxidation, and skeletal transformation proceeded in phosphate buffer to afford an undehydrated derivative of juglorubin. Subsequent dehydration of the secondary alcohol afforded juglorubin. The one-pot synthesis of juglorubin from juglomycin C was also achieved. The photophysical properties of synthetic juglorubin and its derivatives were evaluated.

Total Synthesis of Dendrochrysanene through a Frame Rearrangement.

The first total synthesis of dendrochrysanene (1) was achieved. The key reaction for the construction of dendrochrysanene was an oxidative frame rearrangement reaction from a phenanthrene dimer to a spiro-lactone skeleton, which we serendipitously identified. Owing to the steric hindrance of the substituent on the peri position of the phenanthrene dimer, high-temperature conditions were required for the rearrangement reaction; however, at such temperatures, the substrate decomposed. To address this issue, we added phenylethylamine or benzylamine to the reaction system. We assumed that the amine trapped generated hydrochloric acid and acted as a ligand for iron, helping to maintain an appropriate redox potential. The total synthesis of dendrochrysanene, involving this rearrangement reaction, is an important sequence interlinking phenanthrene derivatives, phenanthrene dimers, and spiro-lactone compounds, which are frequently isolated from plants of Orchidaceae.

Formation of Phenalenone Skeleton by an Unusual Rearrangement Reaction.

The frame rearrangement reaction of dinaphthyl ketones, possessing hydroxy groups at appropriate positions, into phenalenone derivatives under acidic conditions was discovered serendipitously. Although this rearrangement had limited scope, its mechanism was unusual, involving the division of naphthalene rings into one phenalenone ring and one benzene ring. The reaction mechanism was elucidated by direct determination of intermediate structures using 1H NMR measurements. The generated phenalenones are expected to be key intermediates toward natural products and functional materials.

Synthesis and Structures of Zigzag Shaped [12]Cyclo-p-phenylene Composed of Dinaphthofuran Units and Biphenyl Units.

A [12]Cyclo-p-phenylene 9 composed of dinaphthofuran units and biphenyl units was synthesized through reductive elimination of the corresponding trinuclear complex by applying Yamago's method. The X-ray crystallographic analyses of 9 revealed that it adopts a zigzag conformation in the solid state. The UV-vis and fluorescence measurements of compound 9 indicated that it also preferentially took a zigzag conformation in the solution state.