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The intramolecular and long-range ferromagnetic coupling between p-phenylenediamine radical cations in head-to-tail coupled oligo(1, 4-phenyleneethynylene)s and oligo(1,4-phenylenvinylene)s between neighbors and next-nearest neighbors is described. UV/vis/near-IR experiments show that the radical cations are localized in the pendant p-phenylenediamine units of the conjugated oligomers. The ESR spectra of these oligo(1,4-phenyleneethynylene) and oligo(1, 4-phenylenvinylene) di(radical cation)s are consistent with those of a triplet state. A linear behavior is observed for the doubly integrated ESR intensity of the DeltaM(s) = +/-1 and DeltaM(s) = +/-2 signals with the inverse temperature (I approximately 1/T), consistent with Curie's law. This behavior indicates a triplet ground-state diradical with a large triplet-singlet energy gap or possibly a degeneracy of singlet and triplet states. 相似文献
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Martinez-Diaz MV Rodriguez-Morgade MS Feiters MC van Kan PJ Nolte RJ Stoddart JF Torres T 《Organic letters》2000,2(8):1057-1060
[formula: see text] New unsymmetrically substituted DB24C8-phthalocyanines, which are able to form complexes with suitable dialkylammonium cations, have been prepared. These complexes most probably have a pseudorotaxane geometry. 相似文献
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Van Parijs SM Corkeron PJ Harvey J Hayes SA Mellinger DK Rouget PA Thompson PM Wahlberg M Kovacs KM 《The Journal of the Acoustical Society of America》2003,113(6):3403-3410
Comparative analyses of the roar vocalization of male harbor seals from ten sites throughout their distribution showed that vocal variation occurs at the oceanic, regional, population, and subpopulation level. Genetic barriers based on the physical distance between harbor seal populations present a likely explanation for some of the observed vocal variation. However, site-specific vocal variations were present between genetically mixed subpopulations in California. A tree-based classification analysis grouped Scottish populations together with eastern Pacific sites, rather than amongst Atlantic sites as would be expected if variation was based purely on genetics. Lastly, within the classification tree no individual vocal parameter was consistently responsible for consecutive splits between geographic sites. Combined, these factors suggest that site-specific variation influences the development of vocal structure in harbor seals and these factors may provide evidence for the occurrence of vocal dialects. 相似文献
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Lantz MA Hug HJ van Schendel PJ Hoffmann R Martin S Baratoff A Abdurixit A Guntherodt H Gerber C 《Physical review letters》2000,84(12):2642-2645
A low temperature scanning force microscope (SFM) operating in a dynamic mode in ultrahigh vacuum was used to study the Si(111)- (7x7) surface at 7.2 K. Not only the twelve adatoms but also the six rest atoms of the unit cell are clearly resolved for the first time with SFM. In addition, the first measurements of the short range chemical bonding forces above specific atomic sites are presented. The data are in good agreement with first principles computations and indicate that the nearest atoms in the tip and sample relax significantly when the tip is within a few A of the surface. 相似文献