A Semiconducting Organic Radical Cationic Host–Guest Complex

Fahrenbach, Albert C.,Sampath, Srinivasan,Late, Dattatray J.,Barnes, Jonathan C.,Kleinman, Samuel L.,Valley, Nicholas,Hartlieb, Karel J.,Liu, Zhichang,Dravid, Vinayak P.,Schatz, George C.,Van Duyne, R American Chemical Society 2012 ACS NANO Vol.6 No.11

<P>The self-assembly and solid-state semiconducting properties of single crystals of a trisradical tricationic complex composed of the diradical dicationic cyclobis(paraquat-<I>p</I>-phenylene) (CBPQT<SUP>2(•+)</SUP>) ring and methyl viologen radical cation (MV<SUP>•+</SUP>) are reported. An organic field effect transistor incorporating single crystals of the CBPQT<SUP>2(•+)</SUP>⊂MV<SUP>•+</SUP> complex was constructed using lithographic techniques on a silicon substrate and shown to exhibit <I>p</I>-type semiconductivity with a mobility of 0.05 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>. The morphology of the crystals on the silicon substrate was characterized using scanning electron microscopy which revealed that the complexes self-assemble into “molecular wires” observable by the naked-eye as millimeter long crystalline needles. The nature of the recognition processes driving this self-assembly, radical–radical interactions between bipyridinium radical cations (BIPY<SUP>•+</SUP>), was further investigated by resonance Raman spectroscopy in conjunction with theoretical investigations of the vibrational modes, and was supported by X-ray structural analyses of the complex and its free components in both their radical cationic and dicationic redox states. These spectroscopic investigations demonstrate that the bond order of the BIPY<SUP>•+</SUP> radical cationic units of host and guest components is not changed upon complexation, an observation which relates to its conductivity in the solid-state. We envision the modularity inherent in this kind of host–guest complexation could be harnessed to construct a library of custom-made electronic organic materials tailored to fit the specific needs of a given electronic application.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-11/nn303553z/production/images/medium/nn-2012-03553z_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn303553z'>ACS Electronic Supporting Info</A></P>

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

<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>

System Study of the Wireless Multimedia Ad-hoc Network based on IEEE 802.11g

Chung-Wei Lee,Jonathan C.L. Liu,Kun Chen,Yu-Chee Tseng,S.P. Kuo 보안공학연구지원센터 2008 International Journal of Security and Its Applicat Vol.2 No.2

The construction of a wireless multimedia ad-hoc network needs to go across the mixed environment with the indoor, the wall-penetration, and the outdoor condition. This paper presents our contribution to address the system design aspects of a multimedia-enabled network based on IEEE 802.11g ad-hoc mode. There are distinct differences between indoor and outdoor environment and penetrating the walls stressed the system limit of the 802.11g ad-hoc mode. Therefore, routing decisions should be made intelligently with the environmental respect to maximize the bandwidth support on the end-to-end paths. By investigating the experimental results of the average throughput with the 802.11g adhoc mode, we have collected the different performance characteristics among the indoor, the wall-penetration and the outdoor environment. Via the experiments and analyses, we have observed that the ad-hoc mode had the worst performance within 5 meters in indoor environments. In outdoor environments, TCP seemed to favor either short distance (e.g., 5 meters) or long distance (e.g., 25 meters). On the other hand, the best performance UDP has achieved with the distance of 10 meters. When the wall-enetration occurs, it is important that the routing nodes in the building edge areas are placed close-by within 5 meters. Given the solid evidences from the baseline experiments, we have embedded the heuristic algorithms into the routing decisions. We have thus simulated a large area of 300 meters by 300 meters with hundreds of routing nodes. After investigating over 100 (randomlygenerated) topology scenarios, the performance results indicate that our proposed scheme produces the higher-bandwidth paths for most of the cases. Even in the less-dense cases, our proposed schemes still can find the better paths with bandwidth about 30% higher than the conventional methods.

An MST-based network architecture for sharing broadcast TV programs

Chung, Sungwook,Jung, Eun-Sung,Kim, Eunsam,Liu, Jonathan, C.L. IEEE 2010 IEEE communications magazine Vol.48 No.6

<P>With the advent of a consumer device such as a personal video recorder, recent advances in multimedia technologies have led to various enhanced services in the network area. In particular, a fiber channel arbitration loop-based network among PVRs has been presented to demonstrate the feasibility of high-quality content sharing. In addition, a multiple-loop architecture with shared disks, instead of expensive FC switches, has been devised in order to overcome the limit on the number of accommodable PVR users. Nevertheless, there arises the need for a practically constructible topology solution since the multiple-loop architecture is based on complete graph topology that requires the most connectivity for configuration. Therefore, we propose an innovative minimum spanning treebased graph topology for multiple-loop topology organization. The MSG-based multiple-loop architecture can determine the constant average loop size and constant reject ratio, regardless of the number of deployed loops, and the acceptable total traffic with much less connectivity than CG, thereby effectively supporting high-quality live content sharing and distribution between PVRs.</P>