- Bipolaron
= Bipolarons in physics =
In
physics , a bipolaron is a bound pair of twopolaron s. An electron in a material may cause a distortion in the underlying lattice. The combination ofelectron and distortion (which may also be understood as a cloud ofphonon s) is known as apolaron (in part because the interaction between electron andlattice is via apolarization ). When twopolaron s are close together, they can lower their energy by sharing the same distortions, which leads to an effective attraction between thepolaron s. If the interaction is sufficiently large, then that attraction leads to a bound bipolaron. For strong attraction, bipolarons may be small. Small bipolarons have integer spin and thus share some of the properties ofboson s. If many bipolarons form without coming too close, they might be able to form aBose-Einstein condensate . This has led to a suggestion that bipolarons could be a possible mechanism for high temperaturesuperconductivity . For example, they can lead to a very direct interpretation of theisotope effect .Bipolarons in organic chemistry
In
organic chemistry a bipolaron is amolecule or part of amacromolecular chain containing two positivecharge s in aconjugated system . The charges can be located in the centre of the chain or at its termini. Bipolarons andpolaron s are encountered in dopedconducting polymer s such aspolythiophene .It is possible to synthesize and isolate bipolaron model compounds for
X-ray diffraction studies Ref|Zheng. Thediamagnetic bis(triaryl)amine dication 2 in "scheme 1" is prepared from the neutral precursor 1 indichloromethane by reaction with 4 equivalents ofantimony pentachloride . Tworesonance structure s exist for the dication. Structure 2a is a (singlet) diradical and 2b is theclosed shell quinoid . The experimentalbond length s for the central vinylidene group in 2 are 141 pm and 137 pm compared to 144 pm and 134 pm for the precursor 1 implying some contribution from the quinoid structure.On the other hand when a
thiophene unit is added to the core in the structure depicted in "scheme 2", these bond lengths are identical (around 138 pm) making it a true hybrid.See also
*
High temperature superconductivity
*Polaron
*Bose-Einstein condensate
*Phonon
*Electron
*Quinonoid zwitterion sReferences
* "Isolation and Crystal Structures of Two Singlet Bis(Triarylamine) Dications with Nonquinoidal Geometries" Shijun Zheng, Stephen Barlow, Chad Risko, Tiffany L. Kinnibrugh, Viktor N. Khrustalev, Simon C. Jones, Mikhail Yu. Antipin, Neil M. Tucker, Tatiana V. Timofeeva, Veaceslav Coropceanu, Jean-Luc Brédas, and Seth R. Marder
J. Am. Chem. Soc. ; 2006; 128(6) pp 1812 - 1817; [http://dx.doi.org/10.1021/ja0541534 Abstract]
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