RISS 검색 - 국내학술지논문

무료
기관 내 무료
유료

내보내기
내책장담기
한글로보기

정확도순

내림차순

내림차순

10개씩 출력

1
Tetrathiafulvalene Hetero Radical Cation Dimerization in a Redox-Active [2]Catenane

Wang, Cheng,Dyar, Scott M.,Cao, Dennis,Fahrenbach, Albert C.,Horwitz, Noah,Colvin, Michael T.,Carmieli, Raanan,Stern, Charlotte L.,Dey, Sanjeev K.,Wasielewski, Michael R.,Stoddart, J. Fraser American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.46
- 원문보기
The electronic properties of tetrathiafulvalene (TTF) can be tuned by attaching electron-donating or electron-withdrawing substituents. An electron-rich macrocyclic polyether containing two TTF units of different constitutions, namely 4,4′-bis(hydroxymethyl)tetrathiafulvalene (OTTFO) and 4,4′-bisthiotetrathiafulvalene (STTFS), has been synthesized. On two-electron oxidation, a hetero radical dimer is formed between OTTFO•+ and STTFS•+. The redox behavior of the macrocyclic polyether has been investigated by electrochemical techniques and UV–vis and electron paramagnetic resonance (EPR) spectroscopies. The [2]catenane in which the macrocyclic polyether is mechanically interlocked with the cyclobis(paraquat-p-phenylene) (CBPQT4+) ring has also been prepared using template-directed protocols. In the case of the [2]catenane, the formation of the TTF hetero radical dimer is prevented sterically by the CBPQT4+ ring. After a one-electron oxidation, a 70:30 ratio of OTTFO•+ to STTFS•+ is present at equilibrium, and, as a result, two translational isomers of the [2]catenane associated with these electronically different isomeric states transpire. EPR titration spectroscopy and simulations reveal that the radical states of the two constitutionally different TTF units in the [2]catenane still experience long-range electronic intramolecular coupling interactions, despite the presence of the CBPQT4+ ring, when one or both of them are oxidized to the radical cationic state. These findings in the case of both the free macrocyclic polyether and the [2]catenane have led to a deeper fundamental understanding of the mechanism of radical cation dimer formation between constitutionally different TTF units.Graphic Abstract <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-46/ja307577t/production/images/medium/ja-2012-07577t_0013.gif'><A href='http://pubs.acs.org/doi/suppl/10.1021/ja307577t'>ACS Electronic Supporting Info</A>
2
Controlling Switching in Bistable [2]Catenanes by Combining Donor–Acceptor and Radical–Radical Interactions

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
- 원문보기
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 (BIPY2+) units, interlocked mechanically with the tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+), 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 CBPQT4+ ring and DNP, or (ii) radical–radical interactions between CBPQT2(•+) and BIPY•+, 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 1H 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 1H NMR spectroscopy reveals a degenerate rotational motion of the BIPY2+ units in the CBPQT4+ ring for both of the two [2]catenanes, that is governed by a free energy barrier of 14.4 kcal mol–1 for the larger catenane and 17.0 kcal mol–1 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 BIPY2+ 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•+ 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.Graphic Abstract <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'><A href='http://pubs.acs.org/doi/suppl/10.1021/ja3037355'>ACS Electronic Supporting Info</A>
3
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
- 원문보기
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.

내보내기
내책장담기
한글로보기

정확도순

내림차순

내림차순

10개씩 출력

맨처음 페이지로 1 맨끝 페이지로

상세검색

RISS 보유자료

상세검색

해외전자자료

연관 검색어 추천