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A Neutral Naphthalene Diimide [2]Rotaxane
Jacquot de Rouville, Henri-Pierre,Iehl, Julien,Bruns, Carson J.,McGrier, Psaras L.,Frasconi, Marco,Sarjeant, Amy A.,Stoddart, J. Fraser American Chemical Society 2012 ORGANIC LETTERS Vol.14 No.20
<P>A neutral donor–acceptor [2]rotaxane, which has been synthesized using click chemistry, has had its solid-state structure and superstructure elucidated by X-ray crystallography. Both dynamic <SUP>1</SUP>H NMR spectroscopy and electrochemical investigations have been employed in an attempt to shed light on both geometrical reorganization and redox-switching processes that are occurring or can be induced within the [2]rotaxane.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/orlef7/2012/orlef7.2012.14.issue-20/ol3022963/production/images/medium/ol-2012-022963_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ol3022963'>ACS Electronic Supporting Info</A></P>
Zhu, Zhixue,Fahrenbach, Albert C.,Li, Hao,Barnes, Jonathan C.,Liu, Zhichang,Dyar, Scott M.,Zhang, Huacheng,Lei, Juying,Carmieli, Raanan,Sarjeant, Amy A.,Stern, Charlotte L.,Wasielewski, Michael R.,Sto American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.28
<P>Two redox-active bistable [2]catenanes composed of macrocyclic polyethers of different sizes incorporating both electron-rich 1,5-dioxynaphthalene (DNP) and electron-deficient 4,4′-bipyridinium (BIPY<SUP>2+</SUP>) units, interlocked mechanically with the tetracationic cyclophane cyclobis(paraquat-<I>p</I>-phenylene) (CBPQT<SUP>4+</SUP>), were obtained by donor–acceptor template-directed syntheses in a threading-followed-by-cyclization protocol employing Cu(I)-catalyzed azide–alkyne 1,3-dipolar cycloadditions in the final mechanical-bond forming steps. These bistable [2]catenanes exemplify a design strategy for achieving redox-active switching between two translational isomers, which are driven (i) by donor–acceptor interactions between the CBPQT<SUP>4+</SUP> ring and DNP, or (ii) radical–radical interactions between CBPQT<SUP>2(•+)</SUP> and BIPY<SUP>•+</SUP>, respectively. The switching processes, as well as the nature of the donor–acceptor interactions in the ground states and the radical–radical interactions in the reduced states, were investigated by single-crystal X-ray crystallography, dynamic <SUP>1</SUP>H NMR spectroscopy, cyclic voltammetry, UV/vis spectroelectrochemistry, and electron paramagnetic resonance (EPR) spectroscopy. The crystal structure of one of the [2]catenanes in its trisradical tricationic redox state provides direct evidence for the radical–radical interactions which drive the switching processes for these types of mechanically interlocked molecules (MIMs). Variable-temperature <SUP>1</SUP>H NMR spectroscopy reveals a degenerate rotational motion of the BIPY<SUP>2+</SUP> units in the CBPQT<SUP>4+</SUP> ring for both of the two [2]catenanes, that is governed by a free energy barrier of 14.4 kcal mol<SUP>–1</SUP> for the larger catenane and 17.0 kcal mol<SUP>–1</SUP> for the smaller one. Cyclic voltammetry provides evidence for the reversibility of the switching processes which occurs following a three-electron reduction of the three BIPY<SUP>2+</SUP> units to their radical cationic forms. UV/vis spectroscopy confirms that the processes driving the switching are (i) of the donor–acceptor type, by the observation of a 530 nm charge-transfer band in the ground state, and (ii) of the radical–radical ilk in the switched state as indicated by an intense visible absorption (ca. 530 nm) and near-infrared (ca. 1100 nm) bands. EPR spectroscopic data reveal that, in the switched state, the interacting BIPY<SUP>•+</SUP> radical cations are in a fast exchange regime. In general, the findings lay the foundations for future investigations where this radical–radical recognition motif is harnessed in bistable redox-active MIMs in order to achieve close to homogeneous populations of co-conformations in both the ground and switched states.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-28/ja3037355/production/images/medium/ja-2012-037355_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja3037355'>ACS Electronic Supporting Info</A></P>
Room-temperature ferroelectricity in supramolecular networks of charge-transfer complexes
Tayi, Alok S.,Shveyd, Alexander K.,Sue, Andrew C.-H.,Szarko, Jodi M.,Rolczynski, Brian S.,Cao, Dennis,Kennedy, T. Jackson,Sarjeant, Amy A.,Stern, Charlotte L.,Paxton, Walter F.,Wu, Wei,Dey, Sanjeev K. Nature Publishing Group, a division of Macmillan P 2012 Nature Vol.488 No.7412
Materials exhibiting a spontaneous electrical polarization that can be switched easily between antiparallel orientations are of potential value for sensors, photonics and energy-efficient memories. In this context, organic ferroelectrics are of particular interest because they promise to be lightweight, inexpensive and easily processed into devices. A recently identified family of organic ferroelectric structures is based on intermolecular charge transfer, where donor and acceptor molecules co-crystallize in an alternating fashion known as a mixed stack: in the crystalline lattice, a collective transfer of electrons from donor to acceptor molecules results in the formation of dipoles that can be realigned by an external field as molecules switch partners in the mixed stack. Although mixed stacks have been investigated extensively, only three systems are known to show ferroelectric switching, all below 71 kelvin. Here we describe supramolecular charge-transfer networks that undergo ferroelectric polarization switching with a ferroelectric Curie temperature above room temperature. These polar and switchable systems utilize a structural synergy between a hydrogen-bonded network and charge-transfer complexation of donor and acceptor molecules in a mixed stack. This supramolecular motif could help guide the development of other functional organic systems that can switch polarization under the influence of electric fields at ambient temperatures.
A Radically Configurable Six-State Compound
Barnes, J. C.,Fahrenbach, A. C.,Cao, D.,Dyar, S. M.,Frasconi, M.,Giesener, M. A.,Benitez, D.,Tkatchouk, E.,Chernyashevskyy, O.,Shin, W. H.,Li, H.,Sampath, S.,Stern, C. L.,Sarjeant, A. A.,Hartlieb, K. American Association for the Advancement of Scienc 2013 Science Vol.339 No.6118
<P>Most organic radicals possess short lifetimes and quickly undergo dimerization or oxidation. Here, we report on the synthesis by radical templation of a class of air- and water-stable organic radicals, trapped within a homo[2]catenane composed of two rigid and fixed cyclobis(paraquat-p-phenylene) rings. The highly energetic octacationic homo[2]catenane, which is capable of accepting up to eight electrons, can be configured reversibly, both chemically and electrochemically, between each one of six experimentally accessible redox states (0, 2+, 4+, 6+, 7+, and 8+) from within the total of nine states evaluated by quantum mechanical methods. All six of the observable redox states have been identified by electrochemical techniques, three (4+, 6+, and 7+) have been characterized by x-ray crystallography, four (4+, 6+, 7+, and 8+) by electron paramagnetic resonance spectroscopy, one (7+) by superconducting quantum interference device magnetometry, and one (8+) by nuclear magnetic resonance spectroscopy.</P>