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An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation
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Design, synthesis, and study of main chain poly(n-heterocyclic carbene) complexes: applications in electrochromic

Adam B Powell1, Christopher W Bielawski, Alan H Cowley

  • 1Department of Chemistry and Biochemistry and Center for Nano and Molecular Science and Technology, The University of Texas at Austin, 1 University Station, A5300, Austin, Texas 78712-0165, USA.

Journal of the American Chemical Society
|July 9, 2010
PubMed

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The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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