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Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed‐aza[7]helicenes with (1R)‐menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigid π‐frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPL in the visible region, and the high CPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region. [ABSTRACT FROM AUTHOR]

D2‐symmetric (R)‐binaphthyl‐bridged pyrenophanes containing thioether bonds were synthesized. The pyrenophanes exhibited the temperature‐induced sign inversion of circularly polarized luminescence (CPL) while maintaining the emission wavelength and reversibility. The Δglum value reached 0.02, and the FL quenching by heat was negligible. The sign inversion of CPL originates from the inversion of intramolecular excimer chirality associated with excitation dynamics. The two pyrenes form a kinetically trapped left‐handed twist excimer at low temperatures, while they form a thermodynamically favored right‐handed twist excimer at high temperatures. The thioether linkers can impart flexibility suitable for the inversion of chirality of the excimers. [ABSTRACT FROM AUTHOR]

Circularly polarized luminescence (CPL) dyes are recognized to be new generation materials and have been actively developed. Molecular recognition systems provide nice approaches to novel CPL materials, such as stimuli‐responsive switches and chemical sensing materials. CPL may be induced simply by mixing chiral or achiral, luminescent or nonluminescent host and guest; there are several combinations. Molecular recognition can potentially save time and effort to construct well‐ordered chiral structures with noncovalent attractive interactions as compared with the multi‐step synthesis of covalently bonded dyes. It is a challenging subject to engage molecular recognition events with CPL, and it is important and interesting to see how it is achieved. In fact, simple molecular recognition systems can even enable the fine adjustment of CPL performance and detailed conformational/configurational analysis of the excited state. Here we overview the recent achievements of simple host–guest complexes capable of exhibiting CPL, summarizing concisely the host/guest structures, CPL intensities, and characteristics. [ABSTRACT FROM AUTHOR]

BPh3 catalyzes the N‐methylation of secondary amines and the C‐methylenation (methylene‐bridge formation between aromatic rings) of N,N‐dimethylanilines or 1‐methylindoles in the presence of CO2 and PhSiH3; these reactions proceed at 30–40 °C under solvent‐free conditions. In contrast, B(C6F5)3 shows little or no activity. 11B NMR spectra suggested the generation of [HBPh3]−. The detailed mechanism of the BPh3‐catalyzed N‐methylation of N‐methylaniline (1) with CO2 and PhSiH3 was studied by using DFT calculations. BPh3 promotes the conversion of two substrates (N‐methylaniline and CO2) into a zwitterionic carbamate to give three‐component species [Ph(Me)(H)N+CO2−⋅⋅⋅BPh3]. The carbamate and BPh3 act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH3 to generate [HBPh3]−, which is used to produce key CO2‐derived species, such as silyl formate and bis(silyl)acetal, essential for the N‐methylation of 1. DFT calculations also suggested other mechanisms involving water for the generation of [HBPh3]− species. [ABSTRACT FROM AUTHOR]

A series of D2‐symmetric macrocycles composed of alternately linked pyrene and binaphthyl moieties (binaphthyl‐bridged pyrenophanes) have been synthesized. Among them, a pyrenophane possessing ether linkers at the 2,7‐positions of the pyrenes exhibited intense circularly polarized luminescence (CPL) with a |glum| value of 0.053. This value is by far the highest for excimers and was not sensitive to temperature, solvent, or concentration. The CPL originated from a twisting pyrene excimer, with the (R)‐binaphthyl moieties producing a left‐handed twist excimer, which exhibited (−)‐CPL. The electric and magnetic transition dipole moments are perfectly parallel, which is the best relationship for strong CPL. [ABSTRACT FROM AUTHOR]

RutheniumII complexes bearing three axially chiral bipyridyl ligands were synthesized as a new family of chiral complex dyes, and Δ‐(S)‐ and Λ‐(S)‐diastereomers were obtained. The X‐ray crystal structure analyses, spectroscopy, and DFT calculations suggested that all the bipyridyls maintained chirality in both the ground and excited states, and the Δ‐(S)‐ and Λ‐(S)‐isomers are the matched (more relaxed) and mismatched (more constrained) pairs, respectively. The mismatched Λ‐(S)‐isomer exhibited red circularly polarized phosphorescence (CPP) both in solution and in the solid state. The solution state CPP is the most intense of ruthenium complexes, while the solid state CPP is the first example of them. It is supposed that, for the Λ‐(S)‐isomer, the six cumulative CH/π interactions suppress further distortion in the T1 state. [ABSTRACT FROM AUTHOR]

Carbazole‐based aza[7]helicenes and hetero[9]helicenes were successfully obtained via the intramolecular Scholl reaction of 3,6‐bis(biphenyl‐2‐yl)carbazole congeners, while the reaction of 3,6‐bis(naphthylphenyl)‐appended carbazole gave a triple helicene via an unexpected simultaneous double aryl rearrangement. DFT calculations suggested that the rearrangement proceeded via an arenium cation intermediate. In addition, the reaction of methoxy‐appended substrate gave an azahepta[8]circulene via the concurrent C−C bond formation. These helical dyes showed circularly polarized luminescence. The azahepta[8]circulene was further transformed into deeply saddle‐distorted dibenzodiaza[8]circulenes as the first example of its solution‐based synthesis and unambiguous structural determination. [ABSTRACT FROM AUTHOR]

A series of axially chiral 1,1′‐binaphthyls with trialkylsiloxy (OSiR3) groups were synthesized. Among them, 1 a–c possessing OSiR3 groups at the 7,7′‐positions and methyl groups at the 2,2′‐positions were liquids at room temperature, and the neat liquids showed circularly polarized luminescence (CPL) (R=Bu; Φfl,liquid=0.21, |glum,liquid|=1.6×10−3). The |glum,liquid| value is the highest of pure liquids. These compounds remained liquid over a broad range of temperatures, down to −50 °C. Time‐dependent DFT calculations indicated that in the excited state, the binaphthyls adopt a transoid conformation with a small angle between the electric and magnetic transition dipole moments (θμ,m=77°), which is a key factor in their CPL activity. The best binaphthyl dihedral angle in the excited state is approximately 110°. [ABSTRACT FROM AUTHOR]

A variety of carbazolyl‐appended Schiff bases were readily synthesized from 1‐formylcarbazoles and aniline derivatives. Boron complexation of the resulting ligands allowed for facile preparation of new carbazole‐based BODIPY analogues showing solid‐state fluorescence. Furthermore, some dyes were converted into chiral compounds through the Et2AlCl‐mediated incorporation of a binaphthyl unit. The chiral dyes showed aggregation‐induced fluorescence and circularly polarized luminescence (CPL) with the ΦF and glum of up to 0.22 and −3.5×10−3, respectively, in the solid state. The solid‐state fluorescence and CPL were well characterized by the crystal packing analyses and DFT calculations. [ABSTRACT FROM AUTHOR]

Helical carbazole‐based BODIPY analogues were readily synthesized via aza[7]helicenes. The structures of azahelicene‐incorporated BF2 dyes were elucidated by x‐ray diffraction analysis. DFT calculations revealed that the π‐conjugated system expanded from the helicene moiety to the BODIPY framework. The azahelicene‐fused boron complexes showed the Cotton effects and the circularly polarized luminescence (CPL) in the visible region. Furthermore, an axially chiral binaphthyl group was attached to the helically chiral dyes, which enhanced the chiroptical properties. [ABSTRACT FROM AUTHOR]

A series of carbazole‐based boron dipyrromethenes (BODIPYs) 2 a–g bearing binaphthyl units have been synthesized by the Et2AlCl‐mediated reaction of the corresponding BODIPY difluorides 1 a–g with 1,1′‐binaphthalene‐2,2′‐diol. Substituents such as halogen, nitrile, and amino groups were tolerated under the reaction conditions, and the reaction of the phenylethynyl‐substituted 1 h gave (R,R)‐3 h bearing two binaphthyl units. The chiroptical properties of these dyes with different substituents were investigated by UV/Vis, CD, fluorescence, and circularly polarized luminescence (CPL) spectroscopy. The CD spectra showed Cotton effects in the absorption region of the BODIPY moieties. In addition, they showed CPL both in solution and in the solid state. Interestingly, several dyes recorded higher glum values in the solid state, probably due to intermolecular interactions. Because (R,R)‐3 h recorded relatively low glum values, the diastereomer (R,S)‐3 h was prepared. The (R,S) diastereomer showed intense CPL, which suggests a synergetic effect of the two binaphthyl groups. Finally, chiral carbazole‐based BODIPY dimers have been synthesized for the first time and their chiroptical properties were investigated. They showed redshifted fluorescence and CPL, which reached the near‐IR (NIR) region in the solid state. [ABSTRACT FROM AUTHOR]

Unique self‐assembled macrocyclic multinuclear ZnII and NiII complexes with binaphthyl‐bipyridyl ligands (L) were synthesized. X‐ray analysis revealed that these complexes consisted of an outer ring (Zn3L3 or Ni3L3) and an inner core (Zn2 or Ni). In the ZnII complex, the inner Zn2 part rotated rapidly inside the outer ring in solution on an NMR timescale. These complexes exhibited dual catalytic activities for CO2 fixations: synthesis of cyclic carbonates from epoxides and CO2 and temperature‐switched N‐formylation/N‐methylation of amines with CO2 and hydrosilane. [ABSTRACT FROM AUTHOR]

Annulation reactions of the butadiyne-bridged carbazole dimer 1 produced carbazole-based chalcogenaisophlorins 2-4, which were transformed into the corresponding palladium complexes 2Pd-4Pd. The structures were characterized by NMR spectroscopy and X-ray diffraction analysis. Metallation fixed the structures which displayed weak antiaromatic character derived from the 20p isophlorin framework. These complexes showed weak near-infrared (NIR) absorption typical for antiaromatic porphyrinoids in solution. In addition, 2Pd and 3Pd showed relatively strong solid-state NIR absorption. X-ray diffraction analyses of 2Pd and 3Pd revealed trimeric and dimeric stacked layered structures, respectively, and DFT calculations suggest that the solid-state NIR absorption is ascribed to intermolecular charge transfer. [ABSTRACT FROM AUTHOR]

A series of oligonaphthodioxepins was synthesized, revealing a helically arranged octamer, ( R, R, R, R, R, R, R)- 3, which showed intense circularly polarized luminescence (CPL) both in solution and in the solid state. The fluorescence quantum yields (ΦFL) in solution and in the solid state were 0.90 and 0.22, respectively, and the glum values in solution and in the solid state were +2.2×10−3 and +7.0×10−3, respectively. This is one of the highest solid-state CPL glum values yet reported. The high ΦFL and glum values were due to the rigidity, as well as to the fact that ( R, R, R, R, R, R, R)- 3 was a non-planar molecule. Moreover, ( R, R, R, R, R, R, R)- 3 was highly stable both chemically and stereochemically. [ABSTRACT FROM AUTHOR]

Bifunctional ZnII porphyrin catalysts bearing tributylammonium bromide groups at the meta positions of the meso-phenyl groups showed high catalytic activity for the synthesis of cyclic carbonates from epoxides and CO2. Herein, several substituents with different electronic properties were introduced at the para positions. Introduction of electron-donating groups decreased the catalytic activity, whereas the introduction of electron-withdrawing groups increased the activity. The substituents modulated the Lewis acidity of the zinc center, which was confirmed by binding constant experiments. The bifunctional catalyst bearing cyano groups showed the highest catalytic activity with a turnover frequency of up to 42 000 h−1. [ABSTRACT FROM AUTHOR]

Highly active bifunctional metalloporphyrin catalysts were developed for the coupling reaction of epoxides with CO2 to produce cyclic carbonates. The bifunctional catalysts have both quaternary ammonium halide groups and a metal center. To elucidate the roles of these catalytic groups, DFT calculations were performed. Control reactions using tetrabutylammonium halide as a catalyst were also investigated for comparison. In the present article, the results of our computational studies are overviewed. The computational results are consistent with the experimental data and are useful for elucidating the structure-activity relationship. The key features responsible for the high catalytic activity of the bifunctional catalysts are as follows: 1) the cooperative action of the halide anion (nucleophile) and the metal center (Lewis acid); 2) the near-attack conformation, leading to the efficient opening of the epoxide ring in the rate-determining step; and 3) the conformational change of the quaternary ammonium cation to stabilize various anionic species generated during catalysis, in addition to the robustness (thermostability) of the catalysts. [ABSTRACT FROM AUTHOR]

Several carbazole-based boron dipyrromethene (BODIPY) dyes were synthesized by organometallic approaches. Thiazole, benzothiazole, imidazole, benzimidazole, triazole, and indolone substituents were introduced at the 1-position of the carbazole moiety, and boron complexation of each dipyrrin generated the corresponding compounds 1, 2 a, and 3- 6. The properties of these products were investigated by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, X-ray crystallography, and DFT calculations. These compounds exhibited large Stokes shifts, and compounds 1, 2 a, and 3- 5 fluoresced both in solution and in the solid state. Complex 2 a showed the highest fluorescence quantum yield ( ΦF) in the solid state, therefore boron complexes of the carbazole-benzothiazole hybrids 2 b- f, which had several different substituents, were prepared and the effects of the substituents on the photophysical properties of the compounds were examined. The fluorescence properties showed good correlation with the results of crystal-packing analyses, and the dyes exhibited color-tunable solid-state fluorescence. [ABSTRACT FROM AUTHOR]

Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso-phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent-free conditions. The meta-substituted catalysts exhibited high catalytic performance, whereas the para- and ortho-substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta-substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500 h−1 at 170 °C) at an initial CO2 pressure of 1.7 MPa; catalyzed the reaction even at atmospheric CO2 pressure (balloon) at ambient temperature (20 °C); and was applicable to a broad range of substrates, including terminal and internal epoxides. [ABSTRACT FROM AUTHOR]

Highly active bifunctional diporphyrin and triporphyrin catalysts were synthesized through Stille coupling reactions. As compared with a porphyrin monomer, both exhibited improved catalytic activities for the reaction of CO2 with epoxides to form cyclic carbonates, because of the multiple catalytic sites which cooperatively activate the epoxide. Catalytic activities were carefully investigated by controlling temperature, reaction time, and catalyst loading, and very high turnover number and turnover frequency were obtained: 220 000 and 46 000 h−1, respectively, for the magnesium catalyst, and 310 000 and 40 000 h−1, respectively, for the zinc catalyst. Results obtained with a zinc/free-base hybrid diporphyrin catalyst demonstrated that the Br− ions on the adjacent porphyrin moiety also function as nucleophiles. [ABSTRACT FROM AUTHOR]

Proton-bound [M ⋅H ⋅G]+ diastereomeric complexes between some chiral aromatic amino acids or dipeptides (G) and a chiral multifunctional macrocyclic receptor (M=Chirabite-A) undergo, in the gas phase, highly selective substitution and addition reactions by amines, such as 2-aminobutane and piperidine. All the [M ⋅H ⋅G]+ complexes follow time-dependent monoexponential decays. In some cases, the kinetic curves exhibit a plateau revealing the presence of unreactive [M ⋅H ⋅G]+ structures. In them, the amino acid is accommodated in the macrocycle cavity in the zwitterionic form by sharing its acidic hydrogen atoms with the pyridine nitrogen atoms of the host. The same interactions are structurally inaccessible to G=dipeptides or monofunctional amines, which then can be readily released from [M ⋅H ⋅G]+. When the amino acid interacts with the amidocarbonyl oxygen atoms pointing outside the macrocycle cavity, it saves the canonical structure and can be readily displaced by the amine. The Chirabite-A may act as an efficient template for aromatic amino acids by releasing them or not depending upon the amino acid configuration and the basicity of the amine. These unique properties confer to the gas-phase diastereomeric [M ⋅H ⋅G]+ complexes the features of multi-input multi-output chemo-'logic gates'. [ABSTRACT FROM AUTHOR]

Bicyclic compounds with two contiguous tetrasubstituted carbon stereocenters at bridgehead positions were synthesized by N-heterocyclic carbene (NHC)-catalyzed intramolecular crossed benzoin reactions of symmetrical compounds. This desymmetrization strategy was applied to asymmetric synthesis with chiral NHC organocatalysts. Transition-state models were proposed to explain the enantioselectivity. A tricyclic compound with three contiguous tetrasubstituted carbon stereocenters was synthesized by a stepwise strategy. The molecular structure and absolute configuration of the (+)-enantiomer of this tricyclic compound were determined by X-ray crystallographic analysis. [ABSTRACT FROM AUTHOR]

Keywords: chirality; dyes/pigments; heterocycles; luminescence; photophysics EN chirality dyes/pigments heterocycles luminescence photophysics 1 1 1 04/03/20 20200401 NES 200401 B Chiral BODIPY derivatives b and congeners have been recognized as promising circularly polarized luminescence (CPL) dyes. These chiral BODIPY congeners showed CPL both in solution and in the solid state with | I g i SB lum sb | values up to 3.8×10 SP -3 sp in the visible to NIR region. Chirality, dyes/pigments, heterocycles, luminescence, photophysics. [Extracted from the article]

Porphyrinoids CO2 is a cheap, abundant, and nontoxic C1 source, and the chemical conversion of CO2 into useful organic compounds has become increasingly important. In their Full Paper on page 6556 ff., C. Maeda, J. Hasegawa, T. Ema et al. describe the synthesis of bifunctional metalloporphyrins with quaternary ammonium bromides at the meta, para, or ortho positions of the meso‐phenyl groups and investigated their catalytic activities in the formation of cyclic carbonates from epoxides and CO2 under solvent‐free conditions. [ABSTRACT FROM AUTHOR]

A highly active Mg-porphyrin catalyst for the synthesis of cyclic carbonates from epoxides and CO2 under solvent-free conditions showing a TON of up to 103000 is presented. [ABSTRACT FROM AUTHOR]