Phenalenyl-fused porphyrins with different ground states

Zeng, Wangdong,Lee, Sangsu,Son, Minjung,Ishida, Masatoshi,Furukawa, Ko,Hu, Pan,Sun, Zhe,Kim, Dongho,Wu, Jishan Royal Society of Chemistry 2015 Chemical Science Vol.6 No.4

<▼1><P>Fusion of one or two phenalenyl units onto the porphyrin core led to biradicaloids with different ground state, physical property and chemical reactivity.</P></▼1><▼2><P>Materials based on biradicals/biradicaloids have potential applications for organic electronics, photonics and spintronics. In this work, we demonstrated that hybridization of porphyrin and polycyclic aromatic hydrocarbon could lead to a new type of stable biradicals/biradicaloids with tunable ground state and physical property. Mono- and bis-phenalenyl fused porphyrins <B>1</B> and <B>2</B> were synthesized <I>via</I> an intramolecular Friedel–Crafts alkylation-followed-by oxidative dehydrogenation strategy. Our detailed experimental and theoretical studies revealed that <B>1</B> has a closed-shell structure with a small biradical character (<I>y</I> = 0.06 by DFT calculation) in the ground state, while <B>2</B> exists as a persistent triplet biradical at room temperature under inert atmosphere. Compound <B>1</B> underwent hydrogen abstraction from solvent during the crystal growing process while compound <B>2</B> was easily oxidized in air to give two dioxo-porphyrin isomers <B>11a</B>/<B>11b</B>, which can be correlated to their unique biradical character and spin distribution. The physical properties of <B>1</B> and <B>2</B>, their dihydro/tetrahydro-precursors <B>7</B>/<B>10</B>, and the dioxo-compounds <B>11a</B>/<B>11b</B> were investigated and compared.</P></▼2>

Tetrakis(4-<i>tert</i>-butylphenyl) substituted and fused quinoidal porphyrins

Zeng, Wangdong,Lee, Byung Sun,Sung, Young Mo,Huang, Kuo-Wei,Li, Yuan,Kim, Dongho,Wu, Jishan The Royal Society of Chemistry 2012 Chemical communications Vol.48 No.62

<P>4-<I>tert</I>-Butylphenyl-substituted and fused quinoidal porphyrins <B>1</B> and <B>2</B> are prepared for the first time. They show (1) intense one-photon absorption in the far-red/near-infrared region, (2) enhanced two-photon absorption compared with aromatic porphyrin monomers, and (3) amphoteric redox behavior. Their geometry and electronic structure are studied by DFT calculations.</P> <P>Graphic Abstract</P><P>Tetrakis(4-<I>tert</I>-butylphenyl) substituted and fused quinoidal porphyrins are prepared for the first time, which show unique geometry, electronic structure and optical properties. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cc33728b'> </P>

Stable Tetrabenzo-Chichibabin’s Hydrocarbons: Tunable Ground State and Unusual Transition between Their Closed-Shell and Open-Shell Resonance Forms

Zeng, Zebing,Sung, Young Mo,Bao, Nina,Tan, Davin,Lee, Richmond,Zafra, José,L.,Lee, Byung Sun,Ishida, Masatoshi,Ding, Jun,Ló,pez Navarrete, Juan T.,Li, Yuan,Zeng, Wangdong,Kim, Dongho,Huang American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.35

<P>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 <B>1-CS</B> and <B>2-OS</B> 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. <B>1-CS</B> and <B>2-OS</B> exhibited tunable ground states, with a closed-shell quinoidal structure for <B>1-CS</B> and an open-shell biradical form for <B>2-OS</B>. Their corresponding excited-state forms <B>1-OS</B> and <B>2-CS</B> were also chemically approached and showed different decay processes. The biradical <B>1-OS</B> displayed an unusually slow decay to the ground state (<B>1-CS</B>) 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 <B>2-CS</B> (excited state) to the orthogonal biradicaloid <B>2-OS</B> (ground state) happened during the attempted synthesis of <B>2-CS</B>. Compounds <B>1-CS</B> and <B>2-OS</B> can be oxidized into stable dications by FeCl<SUB>3</SUB> and/or concentrated H<SUB>2</SUB>SO<SUB>4</SUB>. The open-shell <B>2-OS</B> also exhibited a large two-photon absorption (TPA) cross section (760 GM at 1200 nm).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-35/ja3050579/production/images/medium/ja-2012-050579_0017.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja3050579'>ACS Electronic Supporting Info</A></P>

Pushing Extended <i>p</i>-Quinodimethanes to the Limit: Stable Tetracyano-oligo(<i>N</i>-annulated perylene)quinodimethanes with Tunable Ground States

Zeng, Zebing,Ishida, Masatoshi,Zafra, José,L.,Zhu, Xiaojian,Sung, Young Mo,Bao, Nina,Webster, Richard D.,Lee, Byung Sun,Li, Run-Wei,Zeng, Wangdong,Li, Yuan,Chi, Chunyan,Navarrete, Juan T. Lo American Chemical Society 2013 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.135 No.16

<P><I>p</I>-Quinodimethane (<I>p</I>-QDM) is a fundamental building block for the design of π-conjugated systems with low band gap and open-shell biradical character. However, synthesis of extended <I>p</I>-QDMs has usually suffered from their intrinsic high reactivity and poor solubility. In this work, benzannulation together with terminal cyano-substitution was demonstrated to be an efficient approach for the synthesis of a series of soluble and stable tetracyano-oligo(<I>N</I>-annulated perylene)quinodimethanes <B><I>n</I>Per-CN</B> (<I>n</I> = 1–6), with the longest molecule having 12 <I>para</I>-linked benzenoid rings! The geometry and electronic structures of these oligomers were investigated by steady-state and transient absorption spectroscopy, nuclear magnetic resonance, electron spin resonance, superconducting quantum interference device, and FT Raman spectroscopy assisted by density functional theory calculations. They showed tunable ground states, varying from a closed-shell quinoidal structure for monomer, to a singlet biradical for dimer, trimer, and tetramer, and to a triplet biradical for pentamer and hexamer. Large two-photon absorption cross-section values were observed in the near-infrared range, which also exhibited a clear chain-length dependence.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2013/jacsat.2013.135.issue-16/ja402467y/production/images/medium/ja-2013-02467y_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja402467y'>ACS Electronic Supporting Info</A></P>

Fluorenyl Based Macrocyclic Polyradicaloids

Lu, Xuefeng,Lee, Sangsu,Hong, Yongseok,Phan, Hoa,Gopalakrishna, Tullimilli Y.,Herng, Tun Seng,Tanaka, Takayuki,Sandoval-Salinas, Marí,a Eugenia,Zeng, Wangdong,Ding, Jun,Casanova, David,Osuka, At American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.37

<P>Synthesis of stable open-shell polyradicaloids including control of intramolecular spin-spin interactions is a challenging topic in organic chemistry and materials science. Herein, we report the synthesis and physical characterization of two series of fluorenyl based macrocyclic polyradicaloids. In one series (FR-MCn, n = 4-6), the fluorenyl radicals are directly linked at 3,6-positions; whereas in the other series (MC-FnAn, n = 3-5), an additional ethynylene moiety is inserted between the neighboring fluorenyl units. To access stable macrocyclic polyradicaloids, three synthetic methods were developed. All of these stable macrocycles can be purified by normal silica gel column chromatography under ambient conditions. In all cases, moderate polyradical characters were calculated by restricted active space spin-flip method due to the moderate intramolecular antiferromagnetic spin-spin interactions. The excitation energies from the low-spin ground state to the lowest high-spin excited state were evaluated by superconducting quantum interference device measurements. Their physical properties were also compared with the respective linear fluorenyl radical oligomers (FR-n, n = 3-6). It is found that the geometry, i.e., the distortional angle and spacer (w or w/o ethynylene) between the neighboring fluorenyl units, has significant effect on their polyradical character, excitation energy, one-photon absorption, two-photon absorption and electrochemical properties. In addition, the macrocyclic tetramers FR-MC4 and MC-F4A4 showed global antiaromatic character due to cyclic pi-conjugation with 36 and 44 pi-electrons, respectively.</P>