Electrochimica Acta 50 (2005) 1469–1474 Novel polythiophene regular copolymers from 3 ′ ,4 ′ -diamino- and 3 ′ ,4 ′ -dinitro-terthiophenes Modulation of electronic properties via post-polymerization functionalization Gianni Zotti a,∗ , Sandro Zecchin a , Gilberto Schiavon a , Barbara Vercelli a , Anna Berlin b,∗∗ a Istituto CNR per l’ Energetica e le Interfasi, C.o Stati Uniti 4, 35127 Padova, Italy b Istituto CNR di Scienze e Tecnologie Molecolari, via C.Golgi 19, 20133 Milano, Italy Abstract Polythiophene regular copolymers bearing amino or nitro moieties directly linked to the conjugated backbone are produced by anodic coupling of 3 ′ ,4 ′ -diamino- or 3 ′ ,4 ′ -dinitro-terthiophenes. The polymers are characterized by cyclic voltammetry, FTIR reflection–absorption and UV–vis spectroscopy and in situ conductivity. Post-polymerization functionalization of polymer films leads to the quantitative trans- formation of the diamine to pyrazine and of the dinitro to diamine and subsequently pyrazine moieties. Conjugation of starting and ending functionalizations with the polythiophene backbone produces dramatic changes in electronic (electrochemical and optical) properties. © 2004 Elsevier Ltd. All rights reserved. Keywords: Conducting polymers; Polythiophene; Electrochemistry; In situ conductivity 1. Introduction During the last years the field of polyconjugated mate- rial has received the contribution of polythiophenes, which regularly alternate thiophene units substituted with various electron-donor (D) or -acceptor (A) moieties. The resulting alternation of electron rich and poor units in the polyconju- gated backbone causes strong changes in the electronic struc- ture, such as the reduction of the optical gap [1], of high interest in organic electronics. In several instances D–A alternation is obtained by the use of nitrogen-based substituents [2–6]. Thus, the pyrazine ring condensed at the 3 and 4 position of the thiophene ring [2] produces by itself a polymer with a low gap (max- imum absorption at 875 nm versus 560 nm for polythio- phene) but alternation of 3,4-ethylenedioxythiophene (D) ∗ Corresponding author. Tel.: +39 049 829 5868; fax: +39 049 829 5853. ∗∗ Co-corresponding author. E-mail address: g.zotti@ieni.cnr.it (G. Zotti). and thieno[3,4-b]pyrazine (A) shows its maximum absorp- tion at a record value of 1430 nm [3]. A polymer alternating dinitro- (A) and diaminothiophene (D) units has been pre- pared chemically [4,5] and showed a maximum absorption at an appreciably low gap (770 nm). We intended to produce polythiophenes in which 3,4- dinitro- or 3,4-diaminothiophene alternates with thio- phene units. This goal is in principle achieved by anodic coupling though no dinitro- or diaminothiophene could previously be polymerized in this way. These 3,4- substituted thiophene units are particularly interesting since they may allow easy post-polymerization functionalization (PPF). PPF of conducting polyconjugated polymers has been pre- viously applied in several instances as reviewed by Ron- cali and co-workers [6]. A general procedure for PPF of soluble poly(3-bromo-4-hexyl-thiophene) via palladium- catalyzed reactions has been recently described [7]. The choice of the 3 ′ ,4 ′ -dinitro- and 3 ′ ,4 ′ -diaminoterthiophenes (Plate 1) as monomers was done with the purpose of 0013-4686/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2004.10.037