Yoshihiro Matano

Cobalt (Co) complexes of porphyrin derivatives possess distinctive redox properties, and hence, their development has attracted significant interest across a wide range of fields. Herein, we report the new examples of the Co complexes of 5,15‐diazaporphyrin (DAP) and 5‐monoazaporphyrin (MAP) derivatives bearing meso ‐aryl groups. These Co complexes were prepared by metal‐templated cyclization of Co–bis(dipyrrin) complexes, complexation of azaporphyrin freebases with a Co salt, and meso ‐N‐functionalization of the Co complexes of DAP and MAP with diphenyliodonium hexafluorophosphate or methyl triflate. The structures as well as the optical and redox properties of these new Co complexes were elucidated by X‐ray crystallography, spectroscopic and voltammetric measurements, and density functional theory calculations. The introduction of a positive charge to the DAP and MAP rings via meso ‐N‐functionalization considerably altered the frontier‐orbital energies, resulting in redshifts of the Q bands and anodic shifts of the ligand‐centered redox processes. The addition of axial ligands also had notable effects on the metal‐centered and ligand‐centered redox processes. All the Co ^II complexes catalyzed the intramolecular radical cyclization and 1,2‐H‐shift reactions of N ‐benzyl‐ N ‐Boc‐3‐diazopropane‐1‐amine in the presence of Cs ₂ CO ₃ to yield two kinds of products via the corresponding σ‐bonded alkyl Co‐azaporphyrin intermediates.

Herein, we report the first examples of group-14 metal complexes of 5-monoazaporphyrins. Six-coordinate silicon(IV) and tin(IV) complexes of 10,15,20-triaryl-5-monoazaporphyrins (Ar3MAPMX2; M = Si or Sn, X = F, Cl, OH, or OCOPh) were prepared by metalation of the freebases of Ar3MAP (Ar3MAPH2) with the corresponding metal salts, followed by sequential axial-ligand exchange reactions. Furthermore, N-phenylation and N-ethynylation reactions of Ar3MAPSiF2 with the corresponding iodonium salts afforded 5,10,15,20-tetraaryl-MAP salts and 5-ethynyl-10,15,20-triaryl-MAP salts, respectively. We also established an environmentally benign method for synthesizing Ar3MAPH2 without a column-separation process. The structures, aromaticity, and optical and electrochemical properties of the SiIV and SnIV complexes of the MAP derivatives were investigated using X-ray crystallography, spectroscopic techniques, cyclic voltammetry, and DFT calculations. The SiIV and SnIV centers stabilized the HOMO and LUMO energy levels and weakened the diatropic ring-current effect of their MAP ligands. The positive charge generated by introducing substituents on the meso nitrogen considerably stabilized the frontier orbitals, resulting in a decrease in aromaticity. Time-resolved fluorescence spectroscopy of fluorescent SiIV complexes also provided valuable information on the effects of the meso-nitrogen atom and its substituents on the excited-state dynamics of MAP chromophores.

There has been great interest in the development of azaporphyrin‐based photosensitizers. Herein, we report a series of group 10 metal (Ni, Pd, Pt) complexes of 10,15,20‐triaryl‐5‐monoazaporphyrin (Ar ₃ MAP; Ar = 4‐MeC ₆ H ₄ ) and their meso ‐N‐substituted derivatives (RAr ₃ MAP; R = Ph, ethynyl, BF ₃ ). The freebase of Ar ₃ MAP, prepared by annulative condensation between 5,10,15‐tris(4‐methylphenyl)bilane and ammonium carbamate in the presence of an iron(III) salt, was converted into metal complexes by treatment with the corresponding metal salts. The copper‐catalyzed meso ‐N‐phenylation of Ar ₃ MAP with a diphenyliodonium salt afforded PhAr ₃ MAP salts. The substantial basicity of the meso ‐N atom of Ar ₃ MAP was further demonstrated by meso ‐N‐ethynylation with an ethynyl(phenyl)iodonium salt and Lewis acid–base complexation with BF ₃ •OEt ₂ . The aromatic character and the optical and redox properties of the new MAP derivatives were assessed using spectroscopic and voltammetric measurements and density functional theory calculations. It was revealed that adding a positive charge to the MAP ring weakened the diatropic ring‐current effect, red‐shifted the Q bands, and anodically shifted the π‐centered redox processes. Transient absorption measurements of the Pd and Pt complexes also provide valuable information regarding the effects of meso ‐N substituents and central metals on the excited‐state dynamics of MAP dyes.

In contrast to the great advances of phthalocyanine‐based materials, the potential of 5,10,15‐triazaporphyrins has not been realized because of the lack of fundamental information about their structure‐property relationships. Here, we report new derivatives of dibenzo‐5,10,15‐triazaporphyrin (DBTriAP) with aryl or alkyl substituents at the meso and/or β positions. Freebases of DBTriAP were prepared by the condensation of two types of 1,9‐dibromodipyrrins with 1,3‐diiminoisoindoline and subsequent functionalization of the β‐pyrrolic carbons. Zinc(II) complexes of DBTriAP were obtained by complexation of the corresponding freebases with zinc(II) acetate. The optical and electrochemical properties of the DBTriAP derivatives were studied by steady‐state and transient ultraviolet/visible absorption/emission spectroscopy, magnetic circular dichroism spectroscopy, cyclic voltammetry (CV), and density functional theory (DFT) calculations. Replacing the β‐pyrrolic hydrogens of the 5‐mesityl‐DBTriAP derivatives with aryl groups resulted in substantial red shifts of the low‐energy absorption band because of the effective π‐delocalization and/or charge‐transfer interaction with the DBTriAP chromophore. The 2,3,17,18‐tetraethyl‐DBTriAP freebase exhibited split redox processes in its cyclic voltammogram, suggesting the rapid formation of a π‐stacked dimer radical cation facilitated by the highly planar structure. Most of the DBTriAP derivatives emitted red fluorescence with quantum yields of 0.07–0.31, indicating their potential as luminescent materials.

Photoresponsive molecules that respond to the surrounding environment are expected to be utilized as optical functional materials, such as sensors. Recently reported 2-aryl-3H-1,3-benzazaphosphole oxide with a diphenylamino group (ABPO) is one such molecule having interesting solvent-dependent properties. The absorption spectra of ABPO in nonpolar and polar solvents are almost identical in shape and excitation energy, whereas the fluorescence spectrum is red-shifted as the solvent polarity increases. In addition, the fluorescence quantum yield drastically decreases in methanol and acetonitrile solvents. In this study, the solvent-dependent optical properties of ABPO were investigated using quantum chemical calculations with solvent models. To describe the solvation structures explicitly, the QM/MM reweighting free energy self-consistent field method was used. The calculated absorption and fluorescence energies qualitatively reproduced the experimental trends. The S₁ excited state has charge-transfer (CT) character with a large dipole moment, which is responsible for the solvent dependency of fluorescence spectra. Furthermore, in addition to the CT state, the twisted intramolecular charge transfer (TICT) state plays an important role in the fluorescence quenching. It was indicated that the stabilization of the TICT state, which has a larger dipole moment than the CT state, affects the decrease in fluorescence quantum yield in polar solvents.

Porphyrinoids in the 20π‐electron state have been extensively studied from the fundamental viewpoint of investigating their structure–antiaromaticity relationships. However, most of the 20π porphyrinoids are highly distorted and unstable in air, which hinder the comprehensive analysis of paratropic ring‐current effects derived from planar π‐electron systems. Herein, we present the first examples of antiaromatic Sn(IV) complexes of 5,10,15,20‐tetraaryl‐5,15‐diazaporphyrinoids (SnX₂TADAPs), prepared by the complexation of the corresponding freebases with Sn(II) chloride under aerobic conditions and subsequent metathesis of the axial ligands, that show paratropic ring‐current effects. Notably, both neutral 20π‐electron derivatives and 19π‐electron radical cations of SnX₂TADAP are extremely stable in air owing to the intrinsic electronic effects of the central Sn(IV) unit and meso nitrogen atoms. NMR spectroscopy, cyclic voltammetry, and density functional theory calculations were performed to assess the ring‐current effects and orbital energies of a series of the 20π‐electron SnX₂TADAPs, and the results reveal that the paratropic ring‐current effects arising from the planar 20π‐electron DAP ring increases with a decrease in the HOMO–LUMO energy gap.

Despite the significant development and extensive application of phthalocyanine and related azaporphyrins, little attention has been paid to meso‐N‐substituted azaporphyrinoids. Here, we report new derivatives of 5,10,20‐triaryl‐5,15‐diazaporphyrinoids (Ar₃DAP), which are reversibly redox‐switchable between the 18π‐ and 19π‐electron state. Four kinds of metal(II) complexes and free bases of Ar₃DAP were prepared by metal‐templated cyclization of metal(II) complexes of 5,10,15‐triaryl‐10‐azabiladiene‐ac with sodium azide or copper‐catalyzed N‐phenylation of 10,20‐diaryl‐5,15‐diazaporphyrins (Ar₂DAP) with diphenyliodonium hexafluorophosphate. In particular, regioselective N‐phenylation of covalently linked Ar₂DAP dimer afforded two kinds of dimers bearing one or two meso‐N‐phenyl groups. Cyclic voltammetry revealed that attaching one aryl group onto the meso‐nitrogen atom markedly changed the redox potentials of the DAP ring. The aromaticity and optical properties of the new Ar₃DAP π‐electron systems were assessed using various spectroscopic measurements and density functional theory calculations. The distribution pattern of an electron spin in the neutral Ar₂DAP–Ar₃DAP radical revealed that the meso‐N‐phenyl group had a remarkable effect on spin delocalization of DAP π‐radical. The present study provides valuable information for understanding the effects of the number of meso‐N‐substituents on azaporphyrin‐based π‐electron systems.

Inclusion of a heteroatom to the phosphole ring is a promising strategy to intrinsically modulate the optical properties of phosphole derivatives. We report on a series of 2‐aryl‐3H‐1,3‐benzazaphosphole oxides that were efficiently prepared via sequential C−P cross‐coupling, dehydrative [3+2] cycloaddition, and ring‐oxidation reactions. The inclusion of one nitrogen atom into the benzophosphole framework caused red shifting of the absorption and emission maxima, reflecting the greater stabilization of the LUMO level. 2‐(2‐Hydroxyphenyl)benzazaphosphole oxide underwent excited state intramolecular proton transfer and emitted a weak fluorescence from the excited state of the N−H tautomer.

We report herein an improved method for the quantitative preparation of free bases of 5,10,15,20-tetraaryl-5,15-diazaporphyrinoid (TADAP) using Me₃SiBr–MeOH to treat the corresponding zinc(II) complexes. Metallation of the free base with HSiCl₃ followed by Si–X metathesis with SbF₃ and redox reactions afforded difluorosilicon(IV) complexes of TADAP.