Hermann John

Publications (5)49.99 Total impact

• Article: Trinuclear cyanines (TNCs) revisited: a new class of electrochromics by intramolecular pi/sigma switching.

  Hermann John, Christoph Briehn, Johann Schmidt, Siegfried Hünig, Jürgen Heinze
  Angewandte Chemie International Edition 02/2007; 46(3):449-53. · 13.45 Impact Factor
• Article: Trinuclear Cyanines (TNCs) Revisited: A New Class of Electrochromics by Intramolecular π/σ Switching

  Hermann John, Christoph Briehn Dr, Johann Schmidt, Siegfried Hünig Prof. Dr, Jürgen Heinze Prof. Dr
  Angewandte Chemie International Edition 12/2006; 46(3):449 - 453. · 13.45 Impact Factor
• Source

  Available from: uni-duesseldorf.de

  Article: Relationship between chain length, disorder, and resistivity in polypyrrole films.

  Carlos Cesar Bof Bufon, Judith Vollmer, Thomas Heinzel, Pamela Espindola, Hermann John, Jürgen Heinze
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  ABSTRACT: The effects of the polymerization temperature and of voltammetric cycling on the chain length and the resistivity of polypyrrole films are investigated. The studies provide further proof for the existence of at least two different types of polypyrrole, the so-called PPy I and PPy II. As the electropolymerization of conjugated systems in contrast to normal polymerization reactions is a fully activated process, the generation of these different types of PPy depends on experimental parameters such as temperature or formation potentials. UV-vis measurements demonstrate that PPy II comprises significantly shorter chains than PPy I (8-12 vs 32-64 units); moreover, film conductivity is found to increase with the fraction of PPy II. This fraction is changed via the polymerization temperature as well as by cyclic voltammetry, both of which can induce a metal-insulator transition. The counter-intuitive relationship between resistivity and chain length is interpreted in terms of disorder-dominated transport, in which the shorter chains of PPy II support the formation of delocalized electronic states, thereby increasing the localization length. Thus, our results are in agreement with recent broadband reflectivity measurements.
  The Journal of Physical Chemistry B 11/2005; 109(41):19191-9. · 3.70 Impact Factor
• Article: 3D-hybrid networks with controllable electrical conductivity from the electrochemical deposition of terthiophene-functionalized polyphenylene dendrimers.

  Hermann John, Roland Bauer, Pamela Espindola, Prashant Sonar, Jürgen Heinze, Klaus Müllen
  Angewandte Chemie International Edition 05/2005; 44(16):2447-51. · 13.45 Impact Factor
• Article: 3,3'- and 4,4'-Dimethoxy-2,2'-bipyrroles: highly electron-rich model compounds for polypyrrole formation.

  Andreas Merz, Sergiy Anikin, Bernd Lieser, Jürgen Heinze, Hermann John
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  ABSTRACT: 3,3'-Dimethoxy-2,2'-bipyrrole (1) and 4,4'-dimethoxy-2,2'-bipyrrole (2) were obtained in short sequences and good yields from N-benzyl-3-hydroxypyrrole-2,4-dicarboxylic acid. The key intermediate leading to 1 is an N-benzyl-3-methoxypyrrole, which is dimerized by lithiation and oxidation with NiCl(2). The formation of 2 is achieved by a classical Ullmann coupling of diethyl 1-benzyl-2-bromo-4-methoxypyrrole-3,5-dicarboxylate. The N-benzyl protection groups of 1 and 2 are cleaved under reducing conditions with sodium in liquid ammonia. Both isomeric bipyrroles are extremely sensitive toward air. Compound 1 has a very low oxidation potential of 0.09 V against AgCl but film formation hardly occurs. On the other hand, compound 2 with a potential of 0.35 V readily forms stable polypyrrole films with anodic waves at -0.51 and -0.35 V and a cathodic wave at -0.77 V, the lowest potential ever observed for a p-doped polymer.
  Chemistry 02/2003; 9(2):449-55. · 5.93 Impact Factor