Copper 1,19-Diaza-21,24-dicarbacorrole: A Corrole Analogue with an N−N Linkage Stabilizes a Ground-State Singlet Organocopper Species

A copper complex of a heterocorrole analogue with an N–N linkage, 1,19-diaza-21,24-dicarbadibenzocorrole ( Cu-5 ), was successfully synthesized via oxidative metalation–cyclization of a tetrapyrrolic precursor. The N–N linkage in the skeleton of Cu-5 , which serves as a mediator of π-electron delocalization, features an 18π aromatic system. The electronic structure of Cu-5 is best described as a ground-state singlet species stabilized by the distinct NNCC coordination core. This finding shows how the ligand's design can be used to modulate the Cu orbital energy, thereby making such compounds invaluable for copper-based catalytic applications.     

meso-Trifluoromethyl-substituted expanded porphyrins

A series of meso-trifluoromethyl-substituted expanded porphyrins, including N-fused [24]pentaphyrin 3, [28]hexaphyrin 4, [32]heptaphyrin 5, [46]decaphyrin 6, and [56]dodecaphyrin 7, were synthesized by means of an acid-catalyzed one-pot condensation reaction of 2-(2,2,2-trifluoro-1-hydroxyethyl)pyrrole (1) as the first examples bearing meso-alkyl substituents. Besides these products, porphyrin 2 and two calix[5]phyrins 8 and 9 were also obtained. [28]Hexaphyrin 4 was quantitatively oxidized to [26]hexaphyrin 14 with MnO(2). These expanded porphyrins have been characterized by mass spectrometry, (1)H and (19)F NMR spectroscopy, and UV/Vis spectroscopy. The single-crystal structures have been determined for 3, 4, 6, 7, and 14. The N-fused [24]pentaphyrin 3 displays a distorted structure containing a tricyclic fused moiety that is similar to those of meso-aryl-substituted counterparts, whereas 8 and 9 are indicated to take roughly planar conformations with an inverted pyrrole opposite to the sp(3)-hybridized meso-carbon atom. Both [28]- and [26]hexaphyrins 4 and 14 have figure-of-eight structures. Solid-state structures of the decaphyrin 6 and dodecaphyrin 7 are remarkable, exhibiting a crescent conformation and an intramolecular two-pitch helical conformation, respectively.     

Periphery-Fused Chiral A2B-Type Subporphyrin

Despite significant interest, the chiroptical properties of subporphyrins have rarely been investigated because chiral subporphyrins are elusive. Here, inherently chiral subporphyrins are elaborated by forming a fused pyran ring at the periphery of an A₂B-type meso-aryl-substituted subporphyrin. Their circular dichroism (CD) properties are largely affected by the peripheral substituents and the dihedral angles between the meso-aryl substituents and the subporphyrin core: the β-perbromo subporphyrin with an orthogonal arrangement of the meso-phenyl substituents to the subporphyrin core exhibits weak CD signals corresponding to the Q bands, whereas the unsubstituted species with smaller dihedral angles shows relatively intense CD signals. A detailed structure–property relationship of these chiral subporphyrins was elucidated by time-dependent (TD) DFT calculations. This study reveals that the CD properties of chiral subporphyrins can be controlled by peripheral substitution and meso-aryl substituents.     

Benzo[c,d]indole‐Containing Aza‐BODIPY Dyes: Asymmetrization‐Induced Solid‐State Emission and Aggregation‐Induced Emission Enhancement as New Properties of a Well‐Known Chromophore

A series of symmetric and asymmetric benzo[c,d]indole‐containing aza boron dipyrromethene (aza‐BODIPY) compounds was synthesized by a titanium tetrachloride‐mediated Schiff‐base formation reaction of commercially available benzo[c,d]indole‐2(1H)‐one and heteroaromatic amines. These aza‐BODIPY analogues show different electronic structures from those of regular aza‐BODIPYs, with hypsochromic shifts of the main absorption compared to their BODIPY counterparts. In addition to the intense fluorescence in solution, asymmetric compounds exhibited solid‐state fluorescence due to significant contribution of the vibronic bands to both absorption and fluorescence as well as reduced fluorescence quenching in the aggregates. Finally, aggregation‐induced emission enhancement, which is rare in BODIPY chromophores, was achieved by introducing a nonconjugated moiety into the core structure.     

Proton dechanneling in alkali halide mixed crystals

The effects of the lattice distortion in KCI-KBr mixed crystals on the dechanneling of 1.5 MeV protons are studied by means of backscattering. The dechanneling rate vs. the composition curve has a maximum at about 1:1 mixture of KCI and KBr. The lattice distortion in the mixed crystals is estimated from the dechanneling rate, and the result agrees well with that obtained by an X-ray measurement. The effective cross-section for the dechanneling caused by the lattice distortion is obtained, and compared with the results of a calculation based on a simple model.     

Effects of carbon-metal-carbon linkages on the optical, photophysical, and electrochemical properties of phosphametallacycle-linked coplanar porphyrin dimers

5-(Diphenylphosphanyl)-10,15,20-triarylporphyrins (meso-phosphanylporphyrins) underwent complexations with palladium(II) and platinum(II) salts to afford phosphapalladacycle- and phosphaplatinacycle-fused coplanar porphyrin dimers, respectively, via regioselective peripheral β-C-H activation of the meso-phosphanylporphyrin ligands. The optical and electrochemical properties of these metal-linked porphyrin dimers as well as their porphyrin monomer/dimer references were investigated by means of steady-state UV-vis absorption/fluorescence spectroscopy, cyclic and differential pulse voltammetry, time-resolved spectroscopy (fluorescence and transient absorption lifetimes and spectra), and magnetic circular dichroism spectroscopy. All the observed data clearly show that the palladium(II) and platinum(II) linkers play crucial roles in the electronic communication between two porphyrin chromophores at the one-electron oxidized state and in the singlet-triplet intersystem-crossing process at the excited state. It has also been revealed that the C-Pt-C linkage makes more significant impacts on these fundamental properties than the C-Pd-C linkage. Furthermore, density functional theory calculations on the metal-linked porphyrin dimers have suggested that the antibonding dπ-pπ orbital interaction between the peripherally attached metal and adjacent pyrrolic β-carbon atoms destabilizes the highest occupied molecular orbitals of the porphyrin π-systems and accounts for the observed unique absorption properties. On the basis of these experimental and theoretical results, it can be concluded that the linear carbon-metal-carbon linkages weakly but definitely perturb the optical, photophysical, and electrochemical properties of the phosphametallacycle-linked coplanar porphyrin dimers.     

Rectangular-shaped expanded phthalocyanines with two central metal atoms

Expanded phthalocyanine (Pc) congeners with two Mo or W central metal ions and four isoindole ring moieties have been synthesized using normal Pc formation conditions in the presence of urea. The products have been characterized by electrochemistry; mass spectrometry (MS); IR, electron paramagnetic resonance (EPR), NMR, electronic absorption, and magnetic circular dichroism (MCD) spectroscopies; and X-ray analysis. The X-ray structures have rectangular C(2v) symmetry and provide evidence that the central Mo atoms are linked by a single bond and coordinated by two isoindole nitrogen atoms and two nitrogen atoms from the amine moieties. The electronic absorption bands extend into the 1200-1500 nm region. This can be explained using Gouterman's four-orbital theory. The experimental NMR data and theoretical calculations provide evidence for a heteroaromatic 22-π-electron conjugation system for the ring-expanded Pc system, which satisfies Hückel's (4n + 2)π aromaticity.     

Gram-Scale Synthesis of Nickel(II) Norcorrole: The Smallest Antiaromatic Porphyrinoid

Small is beautiful: A ring-contracted sister of porphyrin, norcorrole, has been synthesized efficiently as a stable molecule by a nickel-templated strategy. The norcorrole complex is stable but exhibits a distinct antiaromatic character according to the Hückel rule. Oxidation of the norcorrole complex provides an aromatic oxacorrole complex.     

Pyrene‐Bridged Boron Subphthalocyanine Dimers: Combination of Planar and Bowl‐Shaped π‐Conjugated Systems for Creating Uniquely Curved π‐Conjugated Systems

Pyrene‐bridged boron subphthalocyanine dimers were synthesized from a mixed‐condensation reaction of 2,7‐di‐tert‐butyl‐4,5,9,10‐tetracyanopyrene and tetrafluorophthalonitrile, and their syn and anti isomers arising from the result of connecting two bowl‐shaped boron subphthalocyanine molecules were successfully separated. Expansion of the conjugated system of boron subphthalocyanine through a pyrene bridge caused a redshift of the Q band absorption relative to the parent pyrene‐fused monomer, whereas combining the curved π‐conjugation of boron subphthalocyanine with the planar π‐conjugation of pyrene enabled facile embracement of C₆₀ molecules, owing to the enhanced concave–convex π–π stacking interactions.     

An Electron-Accepting aza-BODIPY-Based Donor–Acceptor–Donor Architecture for Bright NIR Emission

A bright near-infrared (NIR) fluorescent molecule was developed based on the donor–acceptor–donor (D–A–D) approach using an aza-BODIPY analog called pyrrolopyrrole aza-BODIPY (PPAB) as an electron-accepting chromophore. Directly introducing electron-donating triphenylamine (TPA) to develop a D–A–D structure caused redshifts of absorption and emission of PPAB into the NIR region with an enhanced fluorescence brightness of up to 5.2×10⁴ m ⁻¹ cm⁻¹, whereas inserting a phenylene linker between the TPA donor and the PPAB acceptor induced solvatochromic behavior in emission. Transient absorption spectra and theoretical calculations revealed the presence of a highly emissive hybridized locally excited and charge-transfer state in the former case and the contribution of the dark charge-separated state to the excited state in the latter case. The bright D–A–D PPAB as a novel emitter resulted in a NIR electroluminescence with a high external quantum efficiency of 3.7 % and a low amplified spontaneous emission threshold of ca. 80 μJ cm⁻², indicating the high potential for NIR optoelectronic applications.