A FULL CHARGE SEPARATION OVER THE TWO SAME CHROMOPHORES IN A PHOTOSYNTHETIC TETRAD

Osuka, Atsuhiro,Marumo, Shinji,Okada, Tadashi,Taniguchi, Seiji,Mataga, Noboru,Ohno, Takeshi,Nozaki, Koichi,Yamazaki, Iwao,Nishimura, Yoshinobu Korean Society of Photoscience 1997 Journal of Photosciences Vol.4 No.3

The synthesis and excited-state dynamics are described for a tetrad (ZC - ZP - ZP - I) consisting of zinc chlorin (ZC), zinc porphyrin (ZP), zinc porphyrin (ZP), and pyromellitimide (I), which upon photoexcitation provides a fully charge-separated state (ZC$^+$- P - ZP - l$^- $) with lifetimes of 230 $\mu$s in THF and > 50$ \mu$s in DMF at room temperature via a stepwise electron-transfer relay that has been detected by the ps-time resolved transient absorption spectroscopy.

Excitation Energy Migration in Multiporphyrin Arrays

황인욱,Atsuhiro Osuka*,김동호,Naoki Aratani 대한화학회 2005 Bulletin of the Korean Chemical Society Vol.26 No.1

During the last decade, the exploration of nanoscale device and circuitry based on molecules has gained increasing interest. In parallel with this, considerable effort is being devoted to the development of molecular photonic/electronic materials based on various porphyrin arrays. This involves light as an input/output signal and excitation energy migration as a mechanism for signal transmission. Absorption of a photon at the light collector end of the porphyrin array yields the excited state, which migrates among the intervening pigments until reaching the emitter, whereupon another photon is emitted. As a consequence, it is relevant to understand the excitation energy transfer (EET) processes occurring in various forms of porphyrin arrays for the applications as artificial light harvesting arrays and molecular photonic/electronic wires. Since the excitonic (dipole) and electronic (conjugation) couplings between the adjacent porphyrin moieties in porphyrin arrays govern the EET processes, we have characterized the EET rates of various forms of multiporphyrin arrays (linear, cyclic, and box) based on various time-resolved spectroscopic measurements. We believe that our observations provide a platform for further development of molecular photonic/electronic materials based on porphyrin arrays.

Möbius aromaticity and antiaromaticity in expanded porphyrins

Yoon, Zin Seok,Osuka, Atsuhiro,Kim, Dongho Nature Publishing Group 2009 Nature chemistry Vol.1 No.2

<P>Aromaticity is a key concept in chemistry, dating back to Faraday's discovery of benzene in 1825 and Kekule's famous alternating-double-bond structure of 1865. In 1858, the Mobius strip was discovered by Mobius and Listing. The Huckel rules for predicting aromaticity, stating that [4n + 2] pi electrons result in an aromatic system, work for planar molecules. Although molecules with Mobius geometry are not found in nature, chemists have tried to synthesize such molecules since the first theoretical prediction by Heilbronner in 1964 and the prediction of Mobius aromaticity for suitable compounds with [4n] pi electrons. However, Mobius-aromatic molecules have proved difficult to synthesize, and sometimes even to identify. Here we summarize recent contributions of several research groups that have succeeded in synthesizing Mobius-type molecules. The results of this survey lead us to suggest that the generation of Mobius topologies in expanded porphyrins is easier than hitherto appreciated.</P>

π-Conjugation Enlargement Toward the Creation of Multi-Porphyrinic Systems with Large Two-Photon Absorption Properties

Aratani, Naoki,Kim, Dongho,Osuka, Atsuhiro Wiley (John WileySons) 2009 Chemistry, an Asian journal Vol.4 No.8

<P>Recent progress in the synthesis of covalently linked porphyrin arrays with large two-Photon absorption (TPA) cross-section values has been reviewed with a particular focus on the relation of TPA properties with molecular structures. Covalently linked porphyrin arrays continue to be important and useful for the creation of functional materials owing to their chemical robustness, fine-tuning, and easy manipulation. More importantly, the porphyrin electronic systems are quite susceptible to periphery conjugative perturbations, hence allowing facile fabrications to extensively delocalized systems. This property has been used for exploration of porphyrin-based molecular systems with large TPA values, demonstrating a general trend that enhancement in electronic interactions leads to large TPA cross-section values. As a representative example, the porphyrin tapes exhibit larger TPA values owing to the fully delocalized nature of the pi-electrons. This Focus Review will help understand the structural requirements of porphyrin arrays with large TPA values, which will be useful for future applications in optical communication in the IR region.</P>

Excitation Energy Migration in Multiporphyrin Arrays

Hwang, In-Wook,Aratani, Naoki,Osuka, Atsuhiro,Kim, Dong-Ho Korean Chemical Society 2005 Bulletin of the Korean Chemical Society Vol.26 No.1

During the last decade, the exploration of nanoscale device and circuitry based on molecules has gained increasing interest. In parallel with this, considerable effort is being devoted to the development of molecular photonic/electronic materials based on various porphyrin arrays. This involves light as an input/output signal and excitation energy migration as a mechanism for signal transmission. Absorption of a photon at the light collector end of the porphyrin array yields the excited state, which migrates among the intervening pigments until reaching the emitter, whereupon another photon is emitted. As a consequence, it is relevant to understand the excitation energy transfer (EET) processes occurring in various forms of porphyrin arrays for the applications as artificial light harvesting arrays and molecular photonic/electronic wires. Since the excitonic (dipole) and electronic (conjugation) couplings between the adjacent porphyrin moieties in porphyrin arrays govern the EET processes, we have characterized the EET rates of various forms of multiporphyrin arrays (linear, cyclic, and box) based on various time-resolved spectroscopic measurements. We believe that our observations provide a platform for further development of molecular photonic/electronic materials based on porphyrin arrays.

Determination of the Superradiance Coherence Length of Directly Linked Linear Porphyrin Arrays at the Single-Molecule Level

Yang, Jaesung,Yoo, Hyejin,Aratani, Naoki,Osuka, Atsuhiro,Kim, Dongho WILEY-VCH Verlag 2009 Angewandte Chemie. international edition Vol.48 No.24

<P>Down to the wire: Photobleaching dynamics show the exciton delocalization length of directly linked porphyrin arrays (see picture) to be about four or five porphyrin units at the single-molecule level. This result provides a better understanding of how light-signal transmission occurs in the solid state and gives a perspective for the porphyrin arrays to be used as single-molecule photonic wires. <img src='wiley_img/14337851-2009-48-24-ANIE200901375-content.gif' alt='wiley_img/14337851-2009-48-24-ANIE200901375-content'> </P> <B>Graphic Abstract</B> <P>Down to the wire: Photobleaching dynamics show the exciton delocalization length of directly linked porphyrin arrays (see picture) to be about four or five porphyrin units at the single-molecule level. This result provides a better understanding of how light-signal transmission occurs in the solid state and gives a perspective for the porphyrin arrays to be used as single-molecule photonic wires. <img src='wiley_img/14337851-2009-48-24-ANIE200901375-content.gif' alt='wiley_img/14337851-2009-48-24-ANIE200901375-content'> </P>

Calix[4]pyrroles bearing proximally <i>meso</i>–<i>meso</i> linking straps: synthesis and anion binding properties

Park, Ja-Young,Skonieczny, Kamil,Aratani, Naoki,Osuka, Atsuhiro,Gryko, Daniel T.,Lee, Chang-Hee The Royal Society of Chemistry 2012 Chemical communications Vol.48 No.65

<P>Calix[4]pyrroles bearing two proximally crossing straps on the same or the opposite sides have been synthesized for the first time. The doubly <I>cis</I>-strapped compound exhibited highly cooperative six-point hydrogen bonding interactions with the anion involving both pyrrolic N–Hs and Ar–Hs.</P> <P>Graphic Abstract</P><P>Calix[4]pyrroles bearing two proximally crossing straps on the same side or the opposite side have been synthesized and characterized. The <I>cis</I>-strapped compound encapsulates the fluoride anion strongly by six-point hydrogen bonding interaction while the <I>trans</I>-strapped compound shows very weak binding. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cc33537a'> </P>

Intramolecular and intermolecular energy transfers in donor-acceptor linear porphyrin arrays

Rhee, Hanju,Joo, Taiha,Aratani, Naoki,Osuka, Atsuhiro,Cho, Sung,Kim, Dongho American Institute of Physics 2006 The Journal of chemical physics Vol.125 No.7

Porphyrin Arch-Tapes: Synthesis, Contorted Structures, and Full Conjugation

Fukui, Norihito,Kim, Taeyeon,Kim, Dongho,Osuka, Atsuhiro American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.26

<P>Porphyrin tapes possessing meso-meso beta-beta beta-beta triple direct linkages have been targets of extensive studies because of their fully conjugated characteristic pi-electronic networks. In this paper, we report porphyrin arch tapes that bear additional carbonyl group(s) or methylene group(s) inserted between one of the beta-beta linkage(s) of the porphyrin tapes. The carbonyl-inserted porphyrin arch-tapes were efficiently synthesized by double fusion reactions of beta-to-beta carbonyl-bridged porphyrin oligomers with DDQ and Sc(OTf)(3), and were converted to the methylene-bridged porphyrin arch-tapes via Luche reduction with NaBH4 and CeCl3 followed by ionic hydrogenation with HBF4 center dot OEt2 and BH3 center dot NEt3. While the conventional porphyrin tapes display rigid and planar structures and low solubilities, these porphyrin arch-tapes show remarkably contorted structures, flexible conformations, and improved solubilities because of the presence of the incorporated seven-membered ring(s). Interestingly, the methylene inserted arch-tapes exhibited conjugative electronic interactions that were comparable to those of porphyrin tapes probably owing to through-space interaction in the contorted conformations. The carbonyl-inserted arch-tapes displayed distinctly larger conjugative interactions owing to an active involvement of the carbonyl group(s) in the electronic conjugation. A similar trend was observed in the nonlinear optical properties, as evidenced by their two-photon absorption cross sections. Furthermore, as a benefit of the contorted structures, these porphyrin arch-tapes can catch C-60 fullerene effectively. Naturally, the electron-rich methylene-bridged arch-tapes exhibited larger association constants than the electron-deficient carbonyl-bridged arch-tapes. Among these arch-tapes, a methylene-bridged syn-Ni(II) porphyrin trimer recorded the largest association constant of (1.5 +/- 0.4) X 10(7) M-1 in toluene at 25 degrees C.</P>

Subporphyrinato Boron(III) Hydrides

Tsurumaki, Eiji,Sung, Jooyoung,Kim, Dongho,Osuka, Atsuhiro American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.3

<P>Subporphyrinato boron(III) hydrides were prepared by reduction of subporphyrinato boron(III) methoxides with diisobutylaluminum hydride (DIBAL-H) in good yields. The authenticity of the B–H bond has been unambiguously confirmed by a <SUP>1</SUP>H NMR signal that appears as a broad quartet at −2.27 ppm with a large coupling constant with the central <SUP>11</SUP>B, characteristic B–H infrared stretching frequencies, and single crystal X-ray diffraction analysis. Red shifts in the corresponding absorption and fluorescence profiles are accounted for in terms of the electron-donating nature of the B-hydride. The hydridic character of subporphyrinato boron(III) hydrides has been demonstrated by the production of H<SUB>2</SUB> via reaction with water or HCl, and controlled reductions of aromatic aldehydes and imines in the presence of a catalytic amount of Ph<SUB>3</SUB>C[B(C<SUB>6</SUB>F<SUB>5</SUB>)<SUB>4</SUB>].</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-3/ja5126269/production/images/medium/ja-2014-126269_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5126269'>ACS Electronic Supporting Info</A></P>