Toward Tetraradicaloid: The Effect of Fusion Mode on Radical Character and Chemical Reactivity

Hu, Pan,Lee, Sangsu,Herng, Tun Seng,Aratani, Naoki,Gonç,alves, Thé,o P.,Qi, Qingbiao,Shi, Xueliang,Yamada, Hiroko,Huang, Kuo-Wei,Ding, Jun,Kim, Dongho,Wu, Jishan American Chemical Society 2016 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.138 No.3

<P>Open-shell singlet diradicaloids display unique electronic, nonlinear optical, and magnetic activity and could become novel molecular materials for organic electronics, photonics, and spintronics. However, design and synthesis of diradicaloids with a significant polyradical character is a challenging task for chemists. In this Article, we report our efforts toward a tetraradicaloid system. A series of potential tetraradicaloids by fusion of two p-quinodimethane (p-QDM) units with naphthalene or benzene rings in different modes were synthesized. Their model compounds containing one p-QDM moiety were also prepared and compared. Their ground-state structures, physical properties, and chemical reactivity were systematically investigated by various experimental methods such as steady-state and transient absorption, two-photon absorption, X-ray crystallographic analysis, electron spin resonance, superconducting quantum interference device, and electrochemistry, assisted by density functional theory calculations. It was found that their diradical and tetraradical characters show a clear dependence on the fusion mode. Upon the introduction of more five-membered rings, the diradical characters greatly decrease. This difference can be explained by the pro-aromaticity/antiaromaticity of the molecules as well as the intramolecular charge transfer. Our comprehensive studies provide a guideline for the design and synthesis of stable open-shell singlet polycyclic hydrocarbons with significant polyradical characters.</P>

Magnetic and Optical Studies of Hydrogenated Cu-doped ZnO Film

Tong Li,Wen Xiao,Tun Seng Herng,Nina Bao,Jun Ding 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12

Significantly enhanced ferromagnetism and strong green emission were observed for Cu-dopedZnO films undergoing a hydrogenation process. After H2 treatment at 500 C, the saturation magnetizationof 2 at% Cu-doped ZnO film (50 nm) is significantly increased from 1.65 emu cm−3(0.3 µB/Cu) to 11.7 emu cm−3 (1.5 µB/Cu). The areal magnetization of the hydrogenated CudopedZnO is dependent on the film thickness, thus suggesting that it is Cu dopants that playdominant roles rather than surface magnetism arising from OH attachment. Detailed XPS and Ramananalysis demonstrated that H2 treatment may introduce more Cu (Cu1+ -like) impurities andoxygen vacancies that coupled with each other, resulting in ferromagnetic ordering. Furthermore,strong green emission can be obtained in hydrogenated Cu-doped ZnO films. The green emissionis unlikely related with Cu dopants, but H2 treatment can generate a unique structure with porousmorphology and coexistence of complex defects that favors the green emission. The “green defects”are not simple O vacancies or H-incorporation and are stable after annealing at 700 C underO2 atmosphere. The high room temperature ferromagnetism and strong green light emission ofhydrogenated Cu-doped ZnO film pave a way to its novel applications in future spintronics andoptoelectronic devices.

Octazethrene and Its Isomer with Different Diradical Characters and Chemical Reactivity: The Role of the Bridge Structure

Hu, Pan,Lee, Sangsu,Park, Kyu Hyung,Das, Soumyajit,Herng, Tun Seng,Gonç,alves, Thé,o P.,Huang, Kuo-Wei,Ding, Jun,Kim, Dongho,Wu, Jishan American Chemical Society 2016 Journal of organic chemistry Vol.81 No.7

<P>The fundamental relationship between structure and diradical character is important for the development of open-shell diradicaloid-based materials. In this work, we synthesized two structural isomers bearing a 2,6-naphthoquinodimethane or a 1,5-naphthoquinodimethane bridge and demonstrated that their diradical characters and chemical reactivity are quite different. The mesityl-or pentafluorophenyl-substituted octazethrene derivatives <B>OZ-M/OZ-F</B> and their isomer <B>OZI-M</B> (with mesityl substituents) were synthesized via an intramolecular Friedel–Crafts alkylation followed by oxidative dehydrogenation strategy from the key building blocks <B>4</B> and <B>11</B>. Our detailed experimental and theoretical studies showed that both isomers have an open-shell singlet ground state with a remarkable diradical character (<I>y</I><SUB>0</SUB> = 0.35 and 0.34 for <B>OZ-M</B> and <B>OZ-F</B>, and <I>y</I><SUB>0</SUB> = 0.58 for <B>OZI-M</B>). Compounds <B>OZ-M</B> and <B>OZ-F</B> have good stability in an ambient environment, while <B>OZI-M</B> has high reactivity and can be easily oxidized to a dioxo product <B>15</B>, which can be correlated to their different diradical characters. Additionally, we investigated the physical properties of <B>OZ-M</B>, <B>OZ-F</B>, and <B>15</B>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/joceah/2016/joceah.2016.81.issue-7/acs.joc.6b00172/production/images/medium/jo-2016-00172x_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jo6b00172'>ACS Electronic Supporting Info</A></P>

Benzo-thia-fused [ <i>n</i> ]thienoacenequinodimethanes with small to moderate diradical characters: the role of pro-aromaticity <i>versus</i> anti-aromaticity

Shi, Xueliang,Quintero, Estefaní,a,Lee, Sangsu,Jing, Linzhi,Herng, Tun Seng,Zheng, Bin,Huang, Kuo-Wei,Ló,pez Navarrete, Juan T.,Ding, Jun,Kim, Dongho,Casado, Juan,Chi, Chunyan Royal Society of Chemistry 2016 Chemical Science Vol.7 No.5

<▼1><P>Pro-aromatic <B>Th<I>n</I>-TIPS</B> exhibits distinctly different physical properties from anti-aromatic <B>S<I>n</I>-TIPS</B>.</P></▼1><▼2><P>Open-shell singlet diradicaloids have recently received much attention due to their unique optical, electronic and magnetic properties and promising applications in materials science. Among various diradicaloids, quinoidal π-conjugated molecules have become the prevailing design. However, the need for a fundamental understanding on how the fusion mode and pro-aromaticity/anti-aromaticity affect their diradical character and physical properties remains unaddressed. In this work, a series of pro-aromatic benzo-thia-fused [<I>n</I>]thienoacenequinodimethanes (<B>Th<I>n</I>-TIPS</B> (<I>n</I> = 1–3) and <B>BDTh-TIPS</B>) were synthesized and compared with the previously reported anti-aromatic bisindeno-[<I>n</I>]thienoacenes (<B>S<I>n</I>-TIPS</B>, <I>n</I> = 1–4). The ground-state geometric and electronic structures of these new quinoidal molecules were systematically investigated by X-ray crystallographic analysis, variable temperature NMR, ESR, SQUID, Raman, and electronic absorption spectroscopy, assisted by DFT calculations. It was found that the diradical character index (<I>y</I><SUB>0</SUB>) increased from nearly zero for <B>Th1-TIPS</B> to 2.4% for <B>Th2-TIPS</B>, 18.2% for <B>Th3-TIPS</B>, and 38.2% for <B>BDTh-TIPS</B>, due to the enhanced aromatic stabilization. Consequently, with the extension of molecular size, the one-photon absorption spectra are gradually red-shifted, the two-photon absorption (TPA) cross section values increase, and the singlet excited state lifetimes decrease. By comparison with the corresponding anti-aromatic analogues <B>S<I>n</I>-TIPS</B> (<I>n</I> = 1–3), the pro-aromatic <B>Th<I>n</I>-TIPS</B> (<I>n</I> = 1–3) exhibit larger diradical character, longer singlet excited state lifetime and larger TPA cross section value. At the same time, they display distinctively different electronic absorption spectra and improved electrochemical amphotericity. Spectroelectrochemical studies revealed a good linear relationship between the optical energy gaps and the molecular length in the neutral, radical cationic and dicationic forms. Our research work discloses a significant difference between the pro-aromatic and anti-aromatic quinoidal compounds and provides guidance for the design of new diradicaloids with desirable properties.</P></▼2>

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>