Photoredox catalysis of acridinium and quinolinium ion derivatives

Fukuzumi Shunichi,이용민,Nam Wonwoo 대한화학회 2025 Bulletin of the Korean Chemical Society Vol.46 No.1

Photoredox catalysis has attracted increasing attention because of wide range of synthetic transformations and solar energy conversion applications. Reviews on photoredox catalysis have so far focused predominantly on the synthetic applications. This review highlights how organic photoredox catalysts were developed and how they function as efficient photocatalysts in mechanistic point of views. In particular, 9‐mesityl‐10‐methylactidinium (Acr + –Mes) has been highlighted as one of the best organic photoredox catalysts. Acr + –Mes was originally developed as a model compound of the photosynthetic reaction center to mimic the long lifetime of the charge‐separated state in which the energy is converted to chemical energy in photosynthesis. The reason why Acr + –Mes acts as one of the most efficient photoredox catalyst is clarified in terms of the one‐electron redox potentials and long lifetimes of the electron‐transfer state (Acr • –Mes •+ ) produced upon photoexcitation of Acr + –Mes in different solvents. The reason why the mesityl substituent at the 9‐position of the Acr + moiety is essential for the efficient photoredox catalysis is discussed in comparison with acridinium ions with different substituents R (Acr + –R) including 10‐methylacridinium ion with no substituent (AcrH + ). The mechanisms of photoredox catalysis of Acr + –Mes are discussed in various synthetic transformations and solar energy conversion reactions mimicking photosynthesis. Photoredox catalysis of quinolinium ion and its derivatives is also discussed in comparison with that of Acr + –Mes. Finally, immobilization of Acr + –Mes and quinolinium ions to form the composite catalysts with redox catalyst is discussed to improve the photoredox catalytic activity and stability. Photoredox catalysis has attracted increasing attention because of wide range of synthetic transformations and solar energy conversion applications. Reviews on photoredox catalysis have so far focused predominantly on the synthetic applications. This review highlights how organic photoredox catalysts were developed and how they function as efficient photocatalysts in mechanistic point of views. In particular, 9-mesityl-10-methylactidinium (Acr+–Mes) has been highlighted as one of the best organic photoredox catalysts. Acr+–Mes was originally developed as a model compound of the photosynthetic reaction center to mimic the long lifetime of the charge-separated state in which the energy is converted to chemical energy in photosynthesis. The reason why Acr+–Mes acts as one of the most efficient photoredox catalyst is clarified in terms of the one-electron redox potentials and long lifetimes of the electrontransfer state (Acr•–Mes•+) produced upon photoexcitation of Acr+–Mes in different solvents. The reason why the mesityl substituent at the 9-position of the Acr+ moiety is essential for the efficient photoredox catalysis is discussed in comparison with acridinium ions with different substituents R (Acr+–R) including 10-methylacridinium ion with no substituent (AcrH+). The mechanisms of photoredox catalysis of Acr+–Mes are discussed in various synthetic transformations and solar energy conversion reactions mimicking photosynthesis. Photoredox catalysis of quinolinium ion and its derivatives is also discussed in comparison with that of Acr+–Mes. Finally, immobilization of Acr+–Mes and quinolinium ions to form the composite catalysts with redox catalyst is discussed to improve the photoredox catalytic activity and stability.

Unusually Large Tunneling Effect on Highly Efficient Generation of Hydrogen and Hydrogen Isotopes in pH-Selective Decomposition of Formic Acid Catalyzed by a Heterodinuclear Iridium−Ruthenium Complex in Water

Fukuzumi, Shunichi,Kobayashi, Takeshi,Suenobu, Tomoyoshi American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.5

<P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-5/ja910349w/production/images/medium/ja-2009-10349w_0005.gif'> <P>A heterodinuclear iridium−ruthenium complex [Ir<SUP>III</SUP>(Cp*)(H<SUB>2</SUB>O)(bpm)Ru<SUP>II</SUP>(bpy)<SUB>2</SUB>](SO<SUB>4</SUB>)<SUB>2</SUB> {<B>1</B>(SO<SUB>4</SUB>)<SUB>2</SUB>, Cp* = η<SUP>5</SUP>-pentamethylcyclopentadienyl, bpm = 2,2′-bipyrimidine, bpy = 2,2′-bipyridine} acts as the most effective catalyst for selective production of hydrogen from formic acid in an aqueous solution at ambient temperature among catalysts reported so far. An unusually large tunneling effect was observed for the first time for the catalytic hydrogen production in H<SUB>2</SUB>O vs D<SUB>2</SUB>O.</P></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja910349w'>ACS Electronic Supporting Info</A></P>

Metal ion-coupled and decoupled electron transfer

Fukuzumi, Shunichi,Ohkubo, Kei Elsevier 2010 Coordination Chemistry Reviews Vol. No.

<P><B>Abstract</B></P><P>Effects of metal ions on thermal and photoinduced electron-transfer reactions from electron donors (D) to electron acceptors (A) are reviewed in terms of metal ion-coupled electron transfer (MCET) vs. metal ion-decoupled electron transfer (MDET). When electron transfer from D to A is coupled with binding of metal ions to A<SUP>−</SUP>, such an electron transfer is defined as MCET in which metal ions accelerate the rates of electron transfer. A number of examples of electron-transfer reactions from D to A, which are energetically impossible to occur, are made possible by strong binding of metal ions to A<SUP>−</SUP> in MCET. The structures of metal ion complexes with A<SUP>−</SUP> are also discussed in relation with the MCET reactivity. The MCET reactivity of metal ions is shown to be enhanced with an increase in the Lewis acidity of metal ions. In contrast to MCET, strong binding of metal ions to A<SUP>−</SUP> results in deceleration of back electron transfer from metal ion complexes of A<SUP>−</SUP> to D<SUP>+</SUP> in the radical ion pair, which is produced by photoinduced electron transfer from D to A in the presence of metal ions, as compared with back electron transfer without metal ions. The deceleration of back electron transfer in the presence of metal ions results from no binding of metal ions to A. This type of electron transfer is defined as metal ion-decoupled electron transfer (MDET). The lifetimes of CS state (D<SUP>+</SUP>–A<SUP>−</SUP>) produced by photoinduced electron transfer from D to A in the D–A linked systems are also elongated by adding metal ions to the D–A systems because of the stabilization of the CS states by strong binding of metal ions to A<SUP>−</SUP> and the resulting slow MDET processes.</P>

Catalytic mechanisms of hydrogen evolution with homogeneous and heterogeneous catalysts

Fukuzumi, Shunichi,Yamada, Yusuke,Suenobu, Tomoyoshi,Ohkubo, Kei,Kotani, Hiroaki Royal Society of Chemistry 2011 Energy & environmental science Vol.4 No.8

<P>This perspective focuses on reaction mechanisms of hydrogen (H<SUB>2</SUB>) evolution with homogeneous and heterogeneous catalysts. First, photocatalytic H<SUB>2</SUB> evolution systems with homogeneous catalysts are discussed from the viewpoint of how to increase the efficiency of the two-electron process for the H<SUB>2</SUB> evolution <I>via</I> photoinduced electron-transfer reactions of metal complexes. Two molecules of the one-electron reduced species of [Rh<SUP>III</SUP>(Cp*)(bpy)(H<SUB>2</SUB>O)](SO<SUB>4</SUB>) (bpy = 2,2′-bipyridine) and [Ir<SUP>III</SUP>(Cp*)(H<SUB>2</SUB>O)(bpm)Ru<SUP>II</SUP>(bpy)<SUB>2</SUB>](SO<SUB>4</SUB>)<SUB>2</SUB> (bpm = 2,2′-bipyrimidine) produced by photoinduced electron-transfer reactions are converted to the two-electron reduced complexes suitable for H<SUB>2</SUB> generation by disproportionation. The photocatalytic mechanism of H<SUB>2</SUB> evolution using Pt nanoparticles as a catalyst is also discussed based on the kinetic analysis of the electron-transfer rates from a photogenerated electron donor to Pt nanoparticles, which are comparable to the overall H<SUB>2</SUB> evolution rates. The electron-transfer rates become faster with increasing proton concentrations with an inverse kinetic isotope effect, when H<SUP>+</SUP> is replaced by D<SUP>+</SUP>. The size and shape effects of Pt nanoparticles on the rates of hydrogen evolution and the electron-transfer reaction are examined to optimize the catalytic efficiency. Finally, catalytic H<SUB>2</SUB> evolution systems from H<SUB>2</SUB> storage molecules are described including shape dependent catalytic activity of Co<SUB>3</SUB>O<SUB>4</SUB> particles for ammonia borane hydrolysis and a large tunneling effect observed in decomposition of formic acid with [Ir<SUP>III</SUP>(Cp*)(H<SUB>2</SUB>O)(bpm)Ru<SUP>II</SUP>(bpy)<SUB>2</SUB>](SO<SUB>4</SUB>)<SUB>2</SUB>.</P> <P>Graphic Abstract</P><P>Recent progress in understanding catalytic mechanisms for hydrogen evolution with homogeneous and heterogeneous catalysts is overviewed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1ee01551f'> </P>

Mimicry and functions of photosynthetic reaction centers

Fukuzumi, Shunichi,Lee, Yong-Min,Nam, Wonwoo Biochemical Society 2018 Biochemical Society transactions Vol.46 No.5

<P>The structure and function of photosynthetic reaction centers (PRCs) have been modeled by designing and synthesizing electron donor-acceptor ensembles including electron mediators, which can mimic multi-step photoinduced charge separation occurring in PRCs to obtain long-lived charge-separated states. PRCs in photosystem I (PSI) or/and photosystem II (PSII) have been utilized as components of solar cells to convert solar energy to electric energy. Biohybrid photoelectrochemical cells composed of PSII have also been developed for solar-driven water splitting into H-2 and O-2. Such a strategy to bridge natural photosynthesis with artificial photosynthesis is discussed in this minireview.</P>

Contrasting Effects of Axial Ligands on Electron-Transfer Versus Proton-Coupled Electron-Transfer Reactions of Nonheme Oxoiron(IV) Complexes

Fukuzumi, Shunichi,Kotani, Hiroaki,Suenobu, Tomoyoshi,Hong, Seungwoo,Lee, Yong-Min,Nam, Wonwoo WILEY-VCH Verlag 2010 Chemistry Vol.16 No.1

<P>The effects of axial ligands on electron-transfer and proton-coupled electron-transfer reactions of mononuclear nonheme oxoiron(IV) complexes were investigated by using [Fe<SUP>IV</SUP>(O)(tmc)(X)]<SUP>n+</SUP> (1-X) with various axial ligands, in which tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is CH<SUB>3</SUB>CN (1-NCCH<SUB>3</SUB>), CF<SUB>3</SUB>COO<SUP>−</SUP> (1-OOCCF<SUB>3</SUB>), or N<SUB>3</SUB><SUP>−</SUP> (1-N<SUB>3</SUB>), and ferrocene derivatives as electron donors. As the binding strength of the axial ligands increases, the one-electron reduction potentials of 1-X (E<SUB>red</SUB>, V vs. saturated calomel electrode (SCE)) are more negatively shifted by the binding of the more electron-donating axial ligands in the order of 1-NCCH<SUB>3</SUB> (0.39) > 1-OOCCF<SUB>3</SUB> (0.13) > 1-N<SUB>3</SUB> (−0.05 V). Rate constants of electron transfer from ferrocene derivatives to 1-X were analyzed in light of the Marcus theory of electron transfer to determine reorganization energies (λ) of electron transfer. The λ values decrease in the order of 1-NCCH<SUB>3</SUB> (2.37) > 1-OOCCF<SUB>3</SUB> (2.12) > 1-N<SUB>3</SUB> (1.97 eV). Thus, the electron-transfer reduction becomes less favorable thermodynamically but more favorable kinetically with increasing donor ability of the axial ligands. The net effect of the axial ligands is the deceleration of the electron-transfer rate in the order of 1-NCCH<SUB>3</SUB> > 1-OOCCF<SUB>3</SUB> > 1-N<SUB>3</SUB>. In sharp contrast to this, the rates of the proton-coupled electron-transfer reactions of 1-X are markedly accelerated in the presence of an acid in the opposite order: 1-NCCH<SUB>3</SUB> < 1-OOCCF<SUB>3</SUB> < 1-N<SUB>3</SUB>. Such contrasting effects of the axial ligands on the electron-transfer and proton-coupled electron-transfer reactions of nonheme oxoiron(IV) complexes are discussed in light of the counterintuitive reactivity patterns observed in the oxo transfer and hydrogen-atom abstraction reactions by nonheme oxoiron(IV) complexes (Sastri et al. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 19 181–19 186).</P> <B>Graphic Abstract</B> <P>Counterintuitive reactivities: The rates of electron transfer (ET) and proton-coupled electron-transfer (PCET) in the reactions of with ferrocene derivatives are markedly affected by the electron-donating ability of the axial ligands (X) in opposite directions (see figure); the electron-donating axial ligand decelerates the ET rate in the reactions, but enhances the PCET reactivity of 1-X in the presence of acid. <img src='wiley_img/09476539-2010-16-1-CHEM200901163-content.gif' alt='wiley_img/09476539-2010-16-1-CHEM200901163-content'> </P>

Fuel Production from Seawater and Fuel Cells Using Seawater

Fukuzumi, Shunichi,Lee, Yong-Min,Nam, Wonwoo Wiley (John WileySons) 2017 ChemSusChem Vol.10 No.22

<P>Seawater is the most abundant resource on our planet and fuel production from seawater has the notable advantage that it would not compete with growing demands for pure water. This Review focuses on the production of fuels from seawater and their direct use in fuel cells. Electrolysis of seawater under appropriate conditions affords hydrogen and dioxygen with 100% faradaic efficiency without oxidation of chloride. Photo-electrocatalytic production of hydrogen from seawater provides a promising way to produce hydrogen with low cost and high efficiency. Microbial solar cells (MSCs) that use biofilms produced in seawater can generate electricity from sunlight without additional fuel because the products of photosynthesis can be utilized as electrode reactants, whereas the electrode products can be utilized as photosynthetic reactants. Another important source for hydrogen is hydrogen sulfide, which is abundantly found in Black Sea deep water. Hydrogen produced by electrolysis of Black Sea deep water can also be used in hydrogen fuel cells. Production of a fuel and its direct use in a fuel cell has been made possible for the first time by a combination of photocatalytic production of hydrogen peroxide from seawater and dioxygen in the air and its direct use in one-compartment hydrogen peroxide fuel cells to obtain electric power.</P>

Synthesis and Photodynamics of 9-Mesitylacridinium Ion-Modified Gold Nanoclusters

Fukuzumi, Shunichi,Hanazaki, Ryo,Kotani, Hiroaki,Ohkubo, Kei American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.32

<P>Photoexcitation of gold nanoclusters covalently functionalized with 9-mesityl-10-methylacridinium ion (Mes-Acr<SUP>+</SUP>) resulted in the formation of the electron-transfer state (Mes<SUP>•+</SUP>-Acr<SUP>•</SUP>), which forms a π-dimer radical cation with the neighboring Mes-Acr<SUP>+</SUP> via an intramolecular π−π interaction.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-32/ja105314x/production/images/medium/ja-2010-05314x_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja105314x'>ACS Electronic Supporting Info</A></P>

Mononuclear Copper Complex-Catalyzed Four-Electron Reduction of Oxygen

Fukuzumi, Shunichi,Kotani, Hiroaki,Lucas, Heather R.,Doi, Kaoru,Suenobu, Tomoyoshi,Peterson, Ryan L.,Karlin, Kenneth D. American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.20

<P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-20/ja100538x/production/images/medium/ja-2010-00538x_0002.gif'> <P>A mononuclear Cu<SUP>II</SUP> complex acts as an efficient catalyst for four-electron reduction of O<SUB>2</SUB> to H<SUB>2</SUB>O. Its reduction by a ferrocene derivative (Fc*) and reaction with O<SUB>2</SUB> leads to the formation of a peroxodicopper(II) complex; this is subsequently reduced by Fc* in the presence of protons to regenerate the Cu<SUP>II</SUP> complex.</P></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja100538x'>ACS Electronic Supporting Info</A></P>

Formation of Ground State Triplet Diradicals from Annulated Rosarin Derivatives by Triprotonation

Fukuzumi, Shunichi,Ohkubo, Kei,Ishida, Masatoshi,Preihs, Christian,Chen, Bo,Borden, Weston Thatcher,Kim, Dongho,Sessler, Jonathan L. American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.31

<P>Annulated rosarins, β,β′-bridged hexaphyrin(1.0.1.0.1.0) derivatives <B>1</B>–<B>3</B>, are formally 24 π-electron antiaromatic species. At low temperature, rosarins <B>2</B> and <B>3</B> are readily triprotonated in the presence of trifluoroacetic acid in dichloromethane to produce ground state triplet diradicals, as inferred from electron paramagnetic resonance (EPR) spectral studies. From an analysis of the fine structure in the EPR spectrum of triprotonated rosarin <B>H</B><SUB><B>3</B></SUB><B>3</B><SUP><B>3+</B></SUP>, a distance of 3.6 Å between the two unpaired electrons was estimated. The temperature dependence of the singlet–triplet equilibrium was determined by means of an EPR titration. Support for these experimental findings came from calculations carried out at the (U)B3LYP/6-31G* level, which served to predict a very low-lying triplet state for the triprotonated form of a simplified model system <B>1</B>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-31/jacs.5b05309/production/images/medium/ja-2015-05309k_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b05309'>ACS Electronic Supporting Info</A></P>