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Ohkubo, Kei,Kawashima, Yuki,Fukuzumi, Shunichi The Royal Society of Chemistry 2012 Chemical communications Vol.48 No.36
<P>A supramolecular binding occurred between lithium ion encapsulated [60]fullerene (Li<SUP>+</SUP>@C<SUB>60</SUB>) and sulfonated tetraphenylporphyrins ([MTPPS]<SUP>4−</SUP> M = H<SUB>2</SUB> and Zn) in a benzonitrile solution. Photoexcitation of Li<SUP>+</SUP>@C<SUB>60</SUB>/[MTPPS]<SUP>4−</SUP> results in formation of a long-lived charge-separated state by photoinduced electron transfer.</P> <P>Graphic Abstract</P><P>Supramolecular complexes were formed between lithium ion encapsulated [60]fullerene (Li<SUP>+</SUP>@C<SUB>60</SUB>) and sulfonated tetraphenylporphyrins in benzonitrile, affording the long-lived triplet charge-separated state by photoinduced electron transfer. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cc31186k'> </P>
Direct Oxygenation of Benzene to Phenol Using Quinolinium Ions as Homogeneous Photocatalysts
Ohkubo, Kei,Kobayashi, Takaki,Fukuzumi, Shunichi WILEY‐VCH Verlag 2011 Angewandte Chemie Vol.123 No.37
<P><B>Die Oxidation von Benzol</B> zu Phenol mit Sauerstoff und Wasser erfolgte in Gegenwart des 3‐Cyano‐1‐methylchinoliniumions als Photokatalysator unter Normalbedingungen (siehe Bild). Der Reaktionsmechanismus wurde durch Detektion des π‐dimeren Benzolradikalkations, das beim lichtinduzierten Elektronentransfer von Benzol zum Photokatalysator entsteht, und durch Beobachtung der Reaktion von Radikalkationen mit Wassermolekülen aufgeklärt.</P>
Ohkubo, Kei,Garcia, Rachel,Sintic, Paul J.,Khoury, Tony,Crossley, Maxwell J.,Kadish, Karl M.,Fukuzumi, Shunichi WILEY-VCH Verlag 2009 Chemistry Vol.15 No.40
<P>The site of electron-transfer reduction of AuPQ<SUP>+</SUP> (PQ=5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quino-xalino[2, 3−b′]porphyrin) and AuQPQ<SUP>+</SUP> (QPQ=5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b′:12,13-b′′]porphyrin) is changed from the Au<SUP>III</SUP> center to the quinoxaline part of the PQ macrocycle in the presence of Sc<SUP>3+</SUP> in benzonitrile because of strong binding of Sc<SUP>3+</SUP> to the two nitrogen atoms of the quinoxaline moiety. Strong binding of Sc<SUP>3+</SUP> to the corresponding nitrogen atoms on the quinoxaline unit of ZnPQ also occurs for the neutral form. The effects of Sc<SUP>3+</SUP> on the photodynamics of an electron donor–acceptor compound containing a linked Zn<SUP>II</SUP> and Au<SUP>III</SUP> porphyrin ([ZnPQ–AuPQ]PF<SUB>6</SUB>) have been examined by femto- and nanosecond laser flash photolysis measurements. The observed transient absorption bands at 630 and 670 nm after laser pulse irradiation in the absence of Sc<SUP>3+</SUP> in benzonitrile are assigned to the charge-shifted (CS) state (ZnPQ<SUP>.</SUP><SUP>+</SUP>–AuPQ). The CS state decays through back electron transfer (BET) to the ground state rather than to the triplet excited state. The BET rate was determined from the disappearance of the absorption band due to the CS state. The decay of the CS state obeys first-order kinetics. The CS lifetime was determined to be 250 ps in benzonitrile. Addition of Sc<SUP>3+</SUP> to a solution of ZnPQ–AuPQ<SUP>+</SUP> in benzonitrile caused a drastic lengthening of the CS lifetime that was determined to be 430 ns, a value 1700 times longer than the 250 ps lifetime measured in the absence of Sc<SUP>3+</SUP>. Such remarkable prolongation of the CS lifetime in the presence of Sc<SUP>3+</SUP> results from a change in the site of electron transfer from the Au<SUP>III</SUP> center to the quinoxaline part of the PQ macrocycle when Sc<SUP>3+</SUP> binds to the quinoxaline moiety, which decelerate BET due to a large reorganization energy of electron transfer. The change in the site of electron transfer was confirmed by ESR measurements, redox potentials, and UV/Vis spectra of the singly reduced products.</P> <B>Graphic Abstract</B> <P>Long lifetime! A dramatic effect of Sc<SUP>3+</SUP> was observed on the electron-transfer reduction of gold(III) quinoxalino- and bisquinoxalinoporphyrins (AuPQ<SUP>+</SUP> and AuQPQ<SUP>+</SUP>) (see figure), which not only changes the site of electron transfer from the Au<SUP>III</SUP> metal to the fused quinoxaline part of the PQ macrocycle, but also leads to a remarkable elongation of the lifetime of the charge-shifted state of a ZnPQ–AuPQ dyad in benzonitrile. This is due to the strong binding of Sc<SUP>3+</SUP> to the ZnPQ and AuPQ<SUP>+</SUP> moieties. <img src='wiley_img/09476539-2009-15-40-CHEM200901105-content.gif' alt='wiley_img/09476539-2009-15-40-CHEM200901105-content'> </P>
Introduction to IEC Standardization for Superconducting Sensors and Detectors
Ohkubo, M. The Korean Superconductivity Society 2012 Progress in superconductivity Vol.14 No.2
Superconducting sensors and detectors have been applied to many fields or beginning to enter the maturing stage. The applications spread over a wide range of fields such as radio telescope, medical examination, quantum information, contamination inspection, materials analysis, etc. For users of the superconducting devices as well as developers, we have to avoid confusion of naming, graphical circuit symbols, and measurement methods for device performance. We are trying to formulate international standards under the International Electrotechnical Commission - Technical Committee 90 (IEC-TC90), which is responsible for superconductivity. The sensors and detectors to be considered are divided into two groups: coherent sensors (SQUID, SIS mixers, etc.) and direct detectors (TES, STJ, MKID, SSPD, etc.).
Ohkubo, Kei,Fujimoto, Atsushi,Fukuzumi, Shunichi Royal Society of Chemistry 2011 Chemical communications Vol.47 No.30
<P>Photooxygenation of cyclohexane by O<SUB>2</SUB> occurs efficiently under visible-light irradiation of an O<SUB>2</SUB>-saturated acetonitrile solution containing 9-mesityl-10-methylacridinium ions (Acr<SUP>+</SUP>–Mes) and HCl to yield cyclohexanone, cyclohexanol and hydrogen peroxide. The photocatalytic reaction is initiated by electron transfer from Cl<SUP>−</SUP> to the mesitylene radical cation moiety.</P> <P>Graphic Abstract</P><P>Photooxygenation of cyclohexane by O<SUB>2</SUB> occurs efficiently under visible-light irradiation of an O<SUB>2</SUB>-saturated acetonitrile solution containing 9-mesityl-10-methylacridinium ions (Acr<SUP>+</SUP>–Mes) and HCl to yield cyclohexanone, cyclohexanol and hydrogen peroxide. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1cc12534f'> </P>
Ohkubo, Kei,Fujimoto, Atsushi,Fukuzumi, Shunichi American Chemical Society 2013 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.135 No.14
<P>Photocatalytic oxygenation of benzene to phenol occurs under visible-light irradiation of 2,3-dichloro-5,6-dicyano-<I>p</I>-benzoquinone (DDQ) in an oxygen-saturated acetonitrile solution of benzene and <I>tert</I>-butyl nitrite. The photocatalytic reaction is initiated by photoinduced electron transfer from benzene to the triplet excited state of DDQ.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2013/jacsat.2013.135.issue-14/ja402303k/production/images/medium/ja-2013-02303k_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja402303k'>ACS Electronic Supporting Info</A></P>
Ohkubo, Kei,Kawashima, Yuki,Sakai, Hayato,Hasobe, Taku,Fukuzumi, Shunichi The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.40
<P>A photoelectrochemical solar cell composed of supramolecular nanoclusters of lithium encapsulated fullerene and zinc sulphonated <I>meso</I>-tetraphenylporphyrin exhibits significant enhancement in the photoelectrochemical performance as compared with the reference system containing only a single component.</P> <P>Graphic Abstract</P><P>A photoelectrochemical solar cell composed of supramolecular nanoclusters of Li<SUP>+</SUP>@C<SUB>60</SUB> and ZnTPPS<SUP>4−</SUP> exhibits significant enhancement in the photoelectrochemical performance. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc41187g'> </P>
Ohkubo, Kei,Mizushima, Kentaro,Iwata, Ryosuke,Fukuzumi, Shunichi Royal Society of Chemistry 2011 Chemical Science Vol.2 No.4
<P>Photocatalytic bromination of aromatic hydrocarbons by molecular oxygen with hydrogen bromide occurs efficiently to produce monobrominated products selectively using 9-mesityl-10-methylacridinium ion (Acr<SUP>+</SUP>–Mes) as a photocatalyst under visible light irradiation. Both the product yield and selectivity for the bromination of 1,3,5-trimethoxybenzene were 100% with a quantum yield of 4.8%. The photocatalytic turnover number is 900 based on the initial concentration of Acr<SUP>+</SUP>–Mes. The reactive radical intermediates involved in the photocatalytic cycle have been successfully detected by laser flash photolysis measurements. The photocatalytic bromination is initiated by photoinduced electron transfer from the mesitylene moiety to the singlet excited state of acridinium ion, which results in formation of the electron-transfer state of Acr<SUP>+</SUP>–Mes (Acr˙–Mes˙<SUP>+</SUP>), followed by electron transfer from aromatic hydrocarbons to the mesitylene radical cation moiety and electron transfer from the acridinyl radical moiety to O<SUB>2</SUB>. The resulting radical cations of aromatic hydrocarbons react with Br<SUP>−</SUP> to produce the corresponding monobrominated products selectively.</P> <P>Graphic Abstract</P><P>Photocatalytic bromination of aromatic hydrocarbons by O<SUB>2</SUB> with HBr occurs efficiently to produce the monobrominated products using 9-mesityl-10-methylacridinium ion. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0sc00535e'> </P>