Unraveling the Remarkable Influence of Substituents on the Emission Variation and Circularly Polarized Luminescence of Dinuclear Aluminum Triple-Stranded Helicates.

This study explored the development of functional dyes using aluminum, focusing on aluminum-based dinuclear triple-stranded helicates, and examined the effects of substituent variations on their structural and optical properties. Key findings revealed that the modification of methyl groups to the pyrrole positions significantly extended the conjugation system, resulting in a red shift in the absorption and emission spectra. Conversely, the modification of methyl groups at the methine positions due to steric hindrances increased the torsion angle of the ligands, leading to a blue shift in the absorption and emission spectra. A common feature across all complexes was that in the excited state, one of the three ligands underwent significant structural relaxation. This led to a pronounced Stokes shift and minimal spectra overlap with high photoluminescence behaviors. Moreover, our research extended to the optical resolution of the newly synthesized complexes by analyzing the chiroptical properties of the resulting enantiomers, including their circular dichroism and circularly polarized luminescence. These insights offer valuable contributions to the design and application of novel aluminum-based functional dyes, potentially influencing a range of fields, from materials science to optoelectronics.

Role of Halobenzene Guest Molecules in Modulating Room Temperature Phosphorescence of Benzophenone-Naphthalene Diimide Inclusion Crystals.

Materials exhibiting room temperature phosphorescence (RTP) have recently emerged as a subject of significant interest. In this study, we successfully created inclusion crystals by introducing halobenzenes as guests into a host molecule combining benzophenone with naphthalene diimide. This approach led to the creation of fascinating fluorescence and RTP properties dependent on the guest molecules. Notably, crystals containing chlorobenzene showed cyan fluorescence, while those with iodobenzene displayed red RTP. This difference highlights the impact of the guest molecule on the luminescent properties, with the significant external heavy-atom effect of iodobenzene playing a key role in promoting efficient intersystem crossing between the excited singlet and triplet states. Crystals with bromobenzene exhibited a unique blend of fluorescence and RTP, both from benzophenone and naphthalene diimide, highlighting the moderate heavy-atom effect. These findings reveal composite materials with remarkably diverse and interesting optical characteristics.

Aqueous Solutions of a Porous Host-Poly-L-lysine Complex with Information on Solids as Different Fluorescence by Guests.

N,N'-Dipyrid-3-yl-1,4,5,8-naphthalenediimide linked to two tris(pentafluorophenyl)borane (1) exhibits strong fluorescence emission in the solid state by the formation of a charge-transfer complex containing small aromatic guest molecules. Hydrophobic 1 was dissolved in water by mixing with poly-L-lysine (PLL) as a solubilizing agent. The 1-PLL complex could include small aromatic guest molecules in water, significantly increasing the fluorescence. The fluorescence maxima of 1 in aqueous solution and solid state were different depending on the guest molecule. Therefore, compound 1 was prepared as aqueous solution with information of fluorescence on solids by complexation with PLL.

Multicomponent Crystals with Competing Intermolecular Interactions: In Situ X-ray Diffraction and Luminescent Features Reveal Multimolecular Assembly under Mechanochemical Conditions.

Supramolecular chemistry under mechanochemical conditions has drawn attention because it can induce low-solubility molecules to self-assemble, although most of the reported examples have been limited to two-component systems. We applied mechanochemical synthesis to achieve multimolecular self-assembly in more challenging three-component systems. The produced crystals showed multicolor solid-state luminescence depending on the components when exposed to UV light. Optical outputs and X-ray diffraction studies were used to examine the self-assembling behavior in greater depth. Using synchrotron radiation, in situ X-ray diffraction permitted direct observation of the milling process, which started the self-assembly process within 1 min. This research emphasizes the importance of multicomponent molecules with optical functions and self-assembling behavior and offers the possibility of developing more complicated multicomponent crystals and organic solid solutions for advanced materials.

Highly Fluorescent Bipyrrole-Based Tetra-BF2 Flag-Hinge Chromophores: Achieving Multicolor and Circularly Polarized Luminescence.

This study reports the facile syntheses of tetra-boron difluoride (tetra-BF2 ) complexes, flag-hinge-like molecules that exhibit intense green-to-orange luminescence in solution and yellow-to-red emission in the solid states. Single-crystal structure analysis and density functional theory calculations suggested a bent structure of this series of compounds. The complexes also exhibited excellent optical properties, with quantum yields reaching 100 % and a large Stokes shift. These properties were attributed to the altered bending angle of the molecule in the S1 excited state. As the rotational motion was suppressed around the 2,2'-bipyrrole axis, atropisomers with axial chirality were formed, which are optically resolvable into (R) and (S)-enantiomers through a chiral column. The atropisomers thus function as circularly polarized luminescent (CPL) materials, in which the color (green, green-yellow, and yellow) can be varied by controlling the aggregation state. This rational design of multi-BF2 complexes can potentially realize novel photofunctional materials.

Insights into Proton Dynamics in a Photofunctional Salt-Cocrystal Continuum: Single-Crystal X-ray, Neutron Diffraction, and Hirshfeld Atom Refinement.

X-ray diffraction, neutron diffraction, and theoretical calculations were used to investigate the relationship between the optical properties and degree of protonation in acid-base complexes. We prepared five acid-base complexes by using a pyridine-modified pyrrolopyrrole derivative and salicylic acid. Two of the prepared acid-base complexes were polymorphs of guest-free crystals with green emission; the other three were guest-inclusion crystals with yellow emission containing CH2 Cl2 , CH2 Br2 , or C2 H4 Cl2 . The presence or absence of guests caused the emission to change color, altering the hydrogen bond strength between the acid-base complexes. Accurate N⋅⋅⋅H distances between the pyridyl moiety and the carboxy group over the temperature range 123 to 273 K were 1.40 Šfor the guest-free crystals and 1.25 Šfor the guest-inclusion crystals. Our findings contribute to a better understanding of the complex relationship between photofunction and proton dynamics in acid-base complexes.

Hydrogen Bond Engineering Visualized by Picometer-Level Distortion of Planar Porphyrin Isomers.

Directly investigating hydrogen bond (HB) dynamics in molecular materials is a challenging task. Here, we report a set of porphyrin isomers, porphycenes, that visualize slight changes on the order of picometers in the intramolecular HB dynamics. Intramolecular HBs of porphycenes were regulated by the systematic modification at meso positions with methyl (Me), cyclopentyl (Cy5), and cyclohexyl (Cy6) moieties. Notably, the quantum yields varied from 35 to 0.04% in chloroform, depending on a slight distortion in the porphycene framework. SC-XRD, XPS, and NMR clearly revealed that the Me and Cy6 moieties increased the nonradiative deactivation by strengthening the intramolecular NH···N HBs whereas Cy5 retained their photoluminescence properties. This is the first example of how the distortion of planar porphyrinoids at the picometer level along with the strength of the intramolecular NH···N HBs can drastically affect their optical properties. The results revealed new avenues of HB engineering based on porphyrinoids.

Electrochemical Synthesis of Cyanoformamides from Trichloroacetonitrile and Secondary Amines Mediated by the B12 Derivative.

The B12 derivative, heptamethyl cobyrinate, -mediated electrochemical synthesis of cyanoformamides has been developed. Aerobic oxygenation of the carbon-centered radical initiated in situ generation of the reactive acyl chloride intermediate, which led to cyanoformamides in the presence of an amine. This one-pot and scalable synthetic method has been demonstrated with 41 examples up to 94% yields with 21 new compounds. The mechanism of electrolysis mediated by the B12 derivative has been proposed based on the DFT calculations.

Room-Temperature Phosphorescence Emitters Exhibiting Red to Near-Infrared Emission Derived from Intermolecular Charge-Transfer Triplet States of Naphthalenediimide-Halobenzoate Triad Molecules.

Invited for the cover of this issue is Toshikazu Ono, Yoshio Hisaeda and co-workers at Kyushu University and their collaborators at Ochanomizu University, Chuo University, and Institute for Molecular Science. The image depicts a molecular assembly structure shining like a jewel, glowing in the red-to-near infrared region. Read the full text of the article at 10.1002/chem.202100906.

Bioinspired Electrolysis for Green Molecular Transformations of Organic Halides Catalyzed by B12 Complex.

Naturally-occurring B12 -dependent enzymes catalyze various molecular transformations that are of particular interest from the viewpoint of biological chemistry as well as synthetic organic chemistry. Inspired by the unique property of the B12 -dependent enzymes, various catalytic reactions have been developed using its model complex. Among the B12 model complexes, heptamethyl cobyrinate, synthesized from natural vitamin B12 , is highly soluble in various organic solvents and a redox active cobalt complex with an excellent catalysis in electroorganic synthesis. The electrochemical dechlorination of pollutant organic chlorides, such as DDT, was effectively catalyzed by the B12 complex. Modification of the electrode surface by the sol-gel method to immobilize the B12 complex was also developed. The B12 modified electrodes were effective for the dehalogenation of organic halides with high turnover numbers based on the immobilized B12 complex. Electrolysis of an organic halide catalyzed by the B12 complex provided dechlorinated products under anaerobic conditions, while the electrolysis under aerobic conditions afforded oxygen incorporated products, such as an ester and amide along with dechlorination. Benzotrichloride was transformed into ethylbenzoate or N,N-diethylbenzamide in the presence of ethanol or diethylamine, respectively. This amide formation was further expanded to a unique paired electrolysis. Electrochemical reductions of an alkene and alkyne were also catalyzed by the B12 complex. A cobalt-hydrogen complex should be formed as a bioinspired intermediate. Using the B12 complex, light-assisted electrosynthesis was also developed to save the applied energy.

One-Pot Synthesis of Tertiary Amides from Organic Trichlorides through Oxygen Atom Incorporation from Air by Convergent Paired Electrolysis.

A convergent paired electrolysis catalyzed by a B12 complex for the one-pot synthesis of a tertiary amide from organic trichlorides (R-CCl3) has been developed. Various readily available organic trichlorides, such as benzotrichloride and its derivatives, chloroform, dichlorodiphenyltrichloroethane (DDT), trichloro-2,2,2-trifluoroethane (CFC-113a), and trichloroacetonitrile (CNCCl3), were converted to amides in the presence of tertiary amines through oxygen incorporation from air at room temperature. The amide formation mechanism in the paired electrolysis, which was mediated by a cobalt complex, was proposed.

Room-Temperature Phosphorescence Emitters Exhibiting Red to Near-Infrared Emission Derived from Intermolecular Charge-Transfer Triplet States of Naphthalenediimide-Halobenzoate Triad Molecules.

Room-temperature phosphorescence (RTP) emitters have attracted significant attention. However, purely organic RTP emitters in red to near-infrared region have not been properly investigated. In this study, a series of naphthalenediimide-halobenzoate-linked molecules are synthesized, one of which exhibits efficient RTP properties, showing red to near-infrared emission in solid and aqueous dispersion. Spectroscopic studies and single-crystal X-ray diffraction analysis have shown that the difference in the stacking modes of compounds affects the optical properties, and the formation of intermolecular charge-transfer complexes of naphthalenediimide-halobenzoate moiety results in a bathochromic shift of absorption and RTP properties. The time-dependent density functional theory calculations showed that the formation of charge-transfer triplet states and the external heavy atom effect of the halogen atom enhance the intersystem crossing between excited singlet and triplet states.

Crystal structures of hydroxymethylbilane synthase complexed with a substrate analog: a single substrate-binding site for four consecutive condensation steps.

Hydroxymethylbilane synthase (HMBS), which is involved in the heme biosynthesis pathway, has a dipyrromethane cofactor and combines four porphobilinogen (PBG) molecules to form a linear tetrapyrrole, hydroxymethylbilane. Enzyme kinetic study of human HMBS using a PBG-derivative, 2-iodoporphobilinogen (2-I-PBG), exhibited noncompetitive inhibition with the inhibition constant being 5.4 ± 0.3 µM. To elucidate the reaction mechanism of HMBS in detail, crystal structure analysis of 2-I-PBG-bound holo-HMBS and its reaction intermediate possessing two PBG molecules (ES2), and inhibitor-free ES2 was performed at 2.40, 2.31, and 1.79 Šresolution, respectively. Their overall structures are similar to that of inhibitor-free holo-HMBS, and the differences are limited near the active site. In both 2-I-PBG-bound structures, 2-I-PBG is located near the terminus of the cofactor or the tetrapyrrole chain. The propionate group of 2-I-PBG interacts with the side chain of Arg173, and its acetate group is associated with the side chains of Arg26 and Ser28. Furthermore, the aminomethyl group and pyrrole nitrogen of 2-I-PBG form hydrogen bonds with the side chains of Gln34 and Asp99, respectively. These amino acid residues form a single substrate-binding site, where each of the four PBG molecules covalently binds to the cofactor (or oligopyrrole chain) consecutively, ultimately forming a hexapyrrole chain. Molecular dynamics simulation of the ES2 intermediate suggested that the thermal fluctuation of the lid and cofactor-binding loops causes substrate recruitment and oligopyrrole chain shift needed for consecutive condensation. Finally, the hexapyrrole chain is hydrolyzed self-catalytically to produce hydroxymethylbilane.

Dinuclear Triple-Stranded Helicates Composed of Tetradentate Ligands with Aluminum(III) Chromophores: Optical Resolution and Multi-color Circularly Polarized Luminescence Properties.

New chiroptical chromophores, dinuclear triple-stranded helicates, composed of tetradentate ligands with aluminum(III) ions, are described. These are synthesized in two steps using inexpensive pyrrole derivatives, hydrazine, and aluminum chloride. These molecular architectures (ALPHY) show multi-color (cyan, yellow, and orange) photoluminescence in solution and in the solid-state, which depends on the substituents of the ligands. The photoluminescence quantum yields of helicates were up to 54 %. The right-handed (P) and left-handed (M) helicates are so stable that they do not undergo racemization in some solvents and are mirror images according to circular dichroism and circularly polarized luminescence (CPL) with an absolute luminescence dissymmetry factor (glum ) of up to the 10-3 order. Mixing the different helicates produces white-light emission with CPL characters. This study offers a glimpse into the potential applications of chromophores with diverse photophysical properties.

Rectangular Holes in Porphyrin Isomers Act As Mono- and Binucleating Ligands: Stereochemistry of Mono- and Diboron Porphycenes and Their Protonation Behaviors.

The first boron complexes of porphycenes, structural isomers of porphyrin, are reported. They are synthesized in good yields by reacting the free-base porphycene ligands with BF3·Et2O through a microwave-assisted method. Depending on the substituent group of porphycenes, two different coordination structures, mono- and diboron porphycenes, are obtained simultaneously. The single crystal structures and DFT calculations suggest that the boron atom of the monoboron porphycene is favorably coordinated on the dipyrroethene site, and the regioisomer of diboron porphycene is of cisoid stereochemistry, which is more stable than transoid. We also investigate the protonation behavior of boron porphycene complexes. Diboron porphycene does not undergo protonation, whereas monoboron porphycene undergoes protonation at the nonboron coordinating pyrroline site, resulting in a red shift in both absorption and emission spectra. Protonation and deprotonation of monoboron porphycene can be reversibly triggered using acids and bases.

Synthesis of a B12-BODIPY dyad for B12-inspired photochemical transformations of a trichloromethylated organic compound.

A B12 complex-BODIPY dyad was synthesized by peripheral modification of cobalamin derivatives. The photophysical properties of the dyad were investigated by UV-vis, PL, and transient absorption spectroscopy. A visible light-driven dechlorination reaction of a trichlorinated organic compound, DDT, was reported. The dyad showed efficient catalysis for dechlorination under N2 with turnover numbers of over 220 for the reaction. One-pot syntheses of an ester and amide from DDT and benzotrichloride were also achieved using the dyad under air.

Electrocatalytic reactivity of imine/oxime-type cobalt complex for direct perfluoroalkylation of indole and aniline derivatives.

Imine/Oxime-type cobalt complexes, regarded as simple vitamin B12 model complexes, were utilized as catalysts for direct C-H perfluoroalkylations of indole and aniline derivatives with nonafluorobutyl iodide (n-C4F9I) as the readily available perfluoroalkyl source. The synthetic approach described herein was performed under mild reaction conditions driven by controlled-potential electrolysis at -0.8 V vs. Ag/AgCl in organic solvents. The mechanistic investigations suggest that a nonafluorobutyl radical is mediated by homolytic cleavage of the cobalt(iii)-carbon bond in the catalytic cycle. This is the first report concerning a fluoroalkylation reaction of (hetero)aromatics catalyzed by the simple vitamin B12 model complex. The convenient electrocatalytic method employing a simple cobalt complex provides a facile synthesis method toward novel fluoroalkylated compounds, demonstrating potential applications in the fields of pharmaceutical chemistry and materials science.

Electrochemically driven, cobalt-carbon bond-mediated direct intramolecular cyclic and acyclic perfluoroalkylation of (hetero)arenes using X(CF2)4X.

A proof-of-concept for the one-step, synthetically challenging cyclic and acyclic perfluoroalkylation of (hetero)arenes driven by the valence change of a vitamin B12 derivative as a cobalt catalyst in the presence of fluoroalkylating reagents (X(CF2)4X) is presented. The consecutive formation of cobalt-carbon bonds and generation of fluoroalkyl radicals by homolysis are the key steps for the reaction to proceed.

Visible light-driven cross-coupling reactions of alkyl halides with phenylacetylene derivatives for C(sp3)-C(sp) bond formation catalyzed by a B12 complex.

Visible light-driven cross-coupling reactions of alkyl halides with phenylacetylene and its derivatives catalyzed by the cobalamin derivative (B12) with the [Ir(dtbbpy)(ppy)2]PF6 photocatalyst at room temperature are reported. The robust B12 catalyst and Ir photocatalyst provided high turnover numbers of over 33 000 for the reactions.

Symmetry Reduction of Porphycenes with Finely Tuned Optical and Electronic Properties through Oxidative Cyclization of E/Z-Mixed Dipyrroethenes.

The main obstacle to the widespread application of porphycenes lies in the lack of efficient and economical methods for their production. Discovery of new synthetic methodologies for porphycene derivatives are important for fine-tuning of their optical and electrochemical properties. Herein, the preparation of a set of AABB-, ABAB-, and ABBA-type meso-tetrasubstituted unsymmetric porphycenes is reported. Their synthesis involved the acid-catalyzed oxidative coupling of AA- and BB-dipyrroethenes, or AB-type dipyrroethenes, as precursors in yields of up to 19 %. The structures were unambiguously confirmed by X-ray crystallography. The type and position of substituents in the unsymmetric porphycenes enabled fine-tuning of the optical and electronic properties, which are discussed in terms of their UV/Vis absorption, fluorescence spectroscopies, cyclic voltammetry, and density functional theory calculations.