|Masatoshi Ishida||Last modified date：2021.06.23|
Assistant Professor / Organic Chemistry of Functional Molecules / Department of Applied Chemistry / Faculty of Engineering
|Masatoshi Ishida||Last modified date：2021.06.23|
|1.||Kazuhisa Yamasumi, Shigeki Mori, Takayuki Tanaka, Masatoshi Ishida, Hiroyuki Furuta, Metal Complexes of 5,10,15-Tris(Pentafluorophenyl)-20-Pyrrolyl N-Confused Porphyrin and Its Meso-Bridged Dimers: Synthesis and Optical Properties, J. Porphyrins Phthalocyanines 2021, 25, 447-455., J. Porphyrins Phthalocyanines, 25, 447-455, 2021.05.|
|2.||Highly porous, N-confused porphyrin-based metal-organic frameworks.|
|3.||Photophysical analysis of 1,10-phenanthroline-embedded porphyrin analogues and their magnesium(II) complexes
The synthesis, characterization, photophysical properties, and theoretical analysis of a series of tetraaza porphyrin analogues (H-Pn: n=1-4) containing a dipyrrin subunit and an embedded 1,10-phenanthroline subunit are described. The meso-phenyl-substituted derivative (H-P1) interacts with a Mg2+ salt (e.g., MgCl2, MgBr2, MgI2, Mg(ClO 4)2, and Mg(OAc)2) in MeCN solution, thereby giving rise to a cation-dependent red-shift in both the absorbance- and emission maxima. In this system, as well as in the other H-Pn porphyrin analogues used in this study, the four nitrogen atoms of the ligand interact with the bound magnesium cation to form Mg2+-dipyrrin-phenanthroline complexes of the general structure MgX-Pn (X=counteranion). Both single-crystal X-ray diffraction analysis of the corresponding zinc-chloride derivative (ZnCl-P1) and fluorescence spectroscopy of the Mg-adducts that are formed from various metal salts provide support for the conclusion that, in complexes such as MgCl-P1, a distorted square-pyramidal geometry persists about the metal cation wherein a chloride anion acts as an axial counteranion. Several analogues (H-Pn) that contain electron-donating and/or electron-withdrawing dipyrrin moieties were prepared in an effort to understand the structure-property relationships and the photophysical attributes of these Mg-dipyrrin complexes. Analysis of various MgX-Pn (X=anion) systems revealed significant substitution effects on their chemical, electrochemical, and photophysical properties, as well as on the Mg2+-cation affinities. The fluorescence properties of MgCl-Pn reflected the effect of donor-excited photoinduced electron transfer (d-PET) processes from the dipyrrin subunit (as a donor site) to the 1,10-phenanthroline acceptor subunit. The proposed d-PET process was analyzed by electron paramagnetic resonance (EPR) spectroscopy and by femtosecond transient absorption (TA) spectroscopy, as well as by theoretical DFT calculations. Taken together, these studies provide support for the suggestion that a radical species is produced as the result of an intramolecular charge-transfer process, following photoexcitation. These photophysical effects, combined with a mixed dipyrrin-phenanthroline structure that is capable of effective Mg 2+-cation complexation, lead us to suggest that porphyrin-inspired systems, such as H-Pn, have a role to play as magnesium-cation sensors. Anything can H-Pn: A new series of tetraaza porphyrin analogues (H-Pn: n=1-4) containing a dipyrrin subunit and an embedded 1,10-phenanthroline subunit have been developed as Mg2+-responsive fluorescent sensors. Upon complexation with Mg2+ ions, a structure-dependent emission enhancement is seen that is partially governed by donor-excited photoinduced electron-transfer (d-PET) events (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim..
|4.||Stable tetrabenzo-Chichibabin's hydrocarbons: Tunable ground state and unusual transition between their closed-shell and open-shell resonance forms
Stable open-shell polycyclic aromatic hydrocarbons (PAHs) are of fundamental interest due to their unique electronic, optical, and magnetic properties and promising applications in materials sciences. Chichibabin's hydrocarbon as a classical open-shell PAH has been investigated for a long time. However, most of the studies are complicated by their inherent high reactivity. In this work, two new stable benzannulated Chichibabin's hydrocarbons 1-CS and 2-OS were prepared, and their electronic structure and geometry in the ground state were studied by various experiments (steady-state and transient absorption spectra, NMR, electron spin resonance (ESR), superconducting quantum interference device (SQUID), FT Raman, X-ray crystallographic etc.) and density function theory (DFT) calculations. 1-CS and 2-OS exhibited tunable ground states, with a closed-shell quinoidal structure for 1-CS and an open-shell biradical form for 2-OS. Their corresponding excited-state forms 1-OS and 2-CS were also chemically approached and showed different decay processes. The biradical 1-OS displayed an unusually slow decay to the ground state (1-CS) due to a large energy barrier (95 ± 2.5 kJ/mol) arising from severe steric hindrance during the transition from an orthogonal biradical form to a butterfly-like quinoidal form. The quick transition from the quinoidal 2-CS (excited state) to the orthogonal biradicaloid 2-OS (ground state) happened during the attempted synthesis of 2-CS. Compounds 1-CS and 2-OS can be oxidized into stable dications by FeCl 3 and/or concentrated H 2SO 4. The open-shell 2-OS also exhibited a large two-photon absorption (TPA) cross section (760 GM at 1200 nm). © 2012 American Chemical Society..
|5.||Cyclo[m]pyridine[n]pyrroles: Hybrid macrocycles that display expanded π-conjugation upon protonation
Novel hybrid cyclo[m]pyridine[n]pyrroles have been synthesized using Suzuki coupling. Their NMR and optical spectroscopic features and solid state structural parameters provide support for the proposal that these species are best described as locally aromatic compounds devoid of long-range intersubunit conjugation. However, an extension of the π-conjugation in the macrocycles can be realized through protonation, as inferred from optical spectroscopic and X-ray diffraction-based structural studies. © 2012 American Chemical Society..
|6.||Donor-Substituted β-functionalized porphyrin dyes on hierarchically structured mesoporous TiO
Novel zinc porphyrin dyes for use in dye-sensitized solar cells (DSSCs) have been synthesized. These dyes are based on a molecular design that relies on donorπ-acceptor interactions, a concept implemented by introducing a bis(4-tert-butylphenyl)amino group at the meso position of the porphyrin opposite to what are 2-propenoic or 2,4-pentadienoic acid anchoring groups at the β-pyrrolic positions. Incorporating an electron-donating group (i.e., the diarylamine) on the porphyrin core serves as the considerable electronic coupling between the donor site and porphyrin core, and hence, the HOMO-LUMO energy gap is decreased. This change is reflected in the remarkable red shift and broadening of the absorption spectra relative to an unfunctionalized parent system. This substitution, in conjunction with functionalization with carboxylic acid moieties on the β-pyrrolic positions, also provides what is an effectively aligned donorπ-acceptor dipolar architecture. This, in turn, gives rise to advantageous charge-transfer properties, including what are significant improvements of the electron injection efficiency on titanium oxide (TiO2) compared to our previous models without a donor substituent. The DSSCs of this study were composed of zero-dimensional hierarchical structured TiO2 spheres with a diameter of 600-800 nm prepared from P-25 and anatase TiO2 nanoparticles, which functioned as the photoelectrodes. With the anatase TiO2-based DSSCs, the power conversion efficiencies (η) as well as the photocurrent action spectra were relatively enhanced, an effect ascribed to the characteristic mesoporous effect and associated electrophysical properties of the anatase TiO2 spheres. Among the dyes prepared in the context of the present study, the doubly functionalized carboxylic acid derivative, tda-2b-bd-Zn, gave rise to the highest power conversion. The η value was 7.47%, and the maximum incident photon-to-current efficiency was 77.3% at the Soret band. The overall η value of tda-2b-bd-Zn is comparable to the performance of typical ruthenium-based dyes, such as N3 (η = 7.68%), under the same conditions. © 2011 American Chemical Society..
|7.||Neutral radical and singlet biradical forms of meso-free, -keto, and -diketo hexaphyrins(22.214.171.124.1.1): Effects on aromaticity and photophysical properties
We have investigated the electronic structures and photophysical properties of 5,10,20,25-tetrakis(pentafluorophenyl)-substituted hexaphyrin(126.96.36.199.1.1) (1) and its meso-keto (2) and meso-diketo derivatives (3) using various spectroscopic measurements. In conjunction with theoretical calculations, these analyses revealed fundamental structure-property relationships within this series, including unusual ground-state electronic structures with neutral, monoradical, and singlet biradical character. The meso-free species 1 is a representative 26 π-electron aromatic compound and shows characteristic spectroscopic features, including a sharp Soret band, well-defined Q-like bands, and a moderately long excited state lifetime (τ = 138 ps). In contrast, the meso-keto derivative 2 displays features characteristic of a neutral monoradical species at the ground state, including the presence of lower energy absorption bands in the NIR spectral region and a relatively short excited-state lifetime (13.9 ps). The meso-diketo 3 exhibits features similar to those of 2, specifically NIR absorptions and a short excited-state lifetime (9.7 ps). Compound 3 is thus assigned as being a ground-state singlet biradicaloid. Two photon absorption (TPA) measurements revealed comparatively large δ(2) values of 600 GM for 2 and 1600 GM for 3 with excitation at λex =1600 nm as compared to that observed for 1 (δ(2): 360 GM). The enhanced nonlinear optical properties of 2 and 3 are rationalized in terms of the open-shell electronic configuration allowing a large, field-induced fluctuation in the electron density (i.e., a large polarization). This interpretation is supported by theoretical evaluations of the static second hyperpolarizabilities (γ) and γ density analyses. Furthermore, nucleus-independent chemical shift (NICS) and harmonic oscillator model of aromaticity (HOMA) values and anisotropy of the induced current density (AICD) plots revealed a clear distinction in terms of the aromatic character of 1-3. Importantly, the open-shell radicaloid 2 and singlet biradicaloid 3 can be formally regarded as 27 π-electron nonaromatic and 26 π-electron aromatic species, respectively, constrained within a dominant 28 π-electron conjugated network. On the basis of the combined experimental and theoretical evidence, it is concluded that the meso-carbonyl groups of 2 and 3 play an important role in perturbing the macrocyclic π-conjugation of the parent hexaphyrin structure 1. In particular, they lead to the imposition of intrinsic radical and biradical character on the molecule as a whole and thus easy-to-discern modifications of the overall electronic effects. © 2011 American Chemical Society..
|8.||Protonation-induced formation of a stable singlet biradicaloid derived from a modified sapphyrin analogue
(Figure Presented) Acid does the trick: A novel 1,10-phenanthroline- embedded sapphyrin analogue 1 (see scheme; R = COOEt, Ar = p-tolyl) bearing meso alkylidenyl double bonds has been synthesized. Interestingly, the protonated form of! ([1-3 H]3+) exhibits singlet biradicaloid character. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim..
|9.||Copper(ii) and nickel(ii) hexafluorophosphate complexes derived from a monoanionic porphyrin analogue:Solvato-and thermochromism of the ni complexes by spin-interconversion
Phenanporphodimethene (1) is a porphyrin analogue which has a dipyrromethene unit replaced by a 1,10-phenanthroline moiety. This modification effectively coverts a dianionic porphyrin to a monoanionic porphyrin analogue with a porphyrin-like N4 coordination sphere. The ligand 1 forms copper and nickel hexafluorophosphate complexes, Cu-1 and Ni-1, respectively. X-ray crystallographic analysis of Cu-1 indicates that the Cu(ii) complex istetracoordinated by two pyrrolic nitrogen atoms and two phenanthrolic nitrogen atoms and includes a non-bondingPF6 counter-anion. The Ni-1 complex has similar geometry with a tetracoordinate square-planar structure in non-coordinating solvents such as CHCl3. In coordinating solvents such as MeOH, the coordinationstructure adopts an octahedral geometry. These results indicate that Ni-1 can be converted from a low-spin tohigh-spin configuration by the coordination of two solvent molecules to the nickel center. This solvatochromic conversion of Ni-1 is accompanied by thermochromic behavior resulting from the transformation between square planar and octahedral configurations in THF solution. The redox peak responsible for the nickel-centered redox reactionof Ni-1 is observed at −0.66 V (vs. Fc/Fc+) in CH2Cl2 solution, which indicates generation of low valent Ni(i) species. Thus, Ni-1 may be useful for future investigations as a novel structural model of the active site of cofactor F430 in methyl-coenzyme M reductase. © 2010 The Royal Society of Chemistry..
|10.||A Porphyrin-related macrocycle with an embedded 1,10-phenanthroline moiety: Fluorescent magnesium(ii) ion sensor
(Figure Presented) Room for accommodation: A novel porphyrin-related macrocycle was constructed by replacement of the dipyrromethene unit with a 1,10-phenanthrollne moiety. This macrocycle is capable of complexation and fluorescent detection of Mg2+ with high selectivity over other physiologically relevant metal ions such as Na+, K+, and Ca2+. It functions well as a fluorescent sensor for Mg2+ even In HEPES buffered aqueous DMSO solution (pH 7.4). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA..