Polythiophenes wide-bandgap

Scheme 15.2 Structures of wide-bandgap polythiophene derivatives...

This chapter focuses on the use of polythiophene derivatives [11] as active electrode materials in electrochemical capacitors. First, the concept of electrochemical capacitors is presented in order to highlight the electrochemical properties of polythiophenes that make them suitable for this application. Second, the various wide- and narrow-bandgap derivatives of polythiophenes that have been investigated are discussed. 

A survey of the polythiophene derivatives that have been considered and tested as active electrode material in electrochemical capacitors can be roughly divided between wide- and narrow-bandgap derivatives. The structure of monomers of the corresponding polymers is presented in Schemes 15.1-15.4. 

Bolognesi and co-workers prepared [3-((o-methoxy)alkylthiophene)s lOa-c by Ni-initiated polymerization of 2,5-diiodothiophenes [34, 35, 36]. A small red shift in EL of polymer 10c, compared with polymer 9e (from 1.8 to 1.95 eV), was presented as an indication of a lower bandgap in the former [31, 34], although it could be the result of asymmetry of the wide emission band (comparison with poly(3-decylthiophene) (P3DT) 9d revealed a smaller blue shift of 0.05 eV [37]. Polymers 10a,b showed high (for polythiophenes) PL quantum yields in solution (38-45 % in THE) that decreased, however, in the films [36], A general... 

Reductive Electropolymerization. Besides the oxidative anodic electropolymerization of the monomer, which is the most convenient and the most widely used method, polythiophene can also be prepared by a cathodic route involving the electroreduction of the complex Ni(2-bromo-5-thienyl)(PPh3)4Br in acetonitrile. This method, initially proposed for the synthesis of poly(p-phenylene) [374-376], has been extended to polythiophene [520]. The major drawback is that the polymer is produced in its neutral insulating form, which leads rapidly to a passivation of the electrode and limits the attainable film thickness to approximately 100 nm. On the other hand, this technique presents the advantage of being applicable to electrode materials subject to anodic corrosion such as small-bandgap semiconductors [521]. 

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