N-substituted dithienopyrroles as electrochemically active monomers: Synthesis, electropolymerization and spectroelectrochemistry of the polymerization products
Renata Rybakiewicz , Łukasz Skórka , G. Louarn , Roman Ganczarczyk , Małgorzata Zagórska , Adam Proń
AbstractTwo new electropolymerizable monomers were synthesized, namely dithieno[3,2-b:2',3'-d]pyrrole N-functionalized with 4-(2-heptylthiazol-4-yl)phenyl (DTP1) and 4-(5-octylthiophen-2-yl)phenyl (DTP2) groups. Both monomers readily electropolymerize to yield the corresponding polyDTP1 and polyDTP2. Electrochemically determined ionization potential (IP) of both polymers (about 4.75 eV) are higher than IPs of poly(dithieno[3,2-b:2',3'-d]pyrrole) N-substituted with alkyl or alkylphenyl groups. This finding, corroborated by DFT calculations, suggests that electron accepting nature of (thiazol-4-yl)phenyl and (thiophen-2-yl)phenyl substituents lowers the pi-electron density in the dithienopyrrole moiety making the polymers oxidation more difficult. Optical band gaps of polyDTP1 (E-g opt = 1.76 eV) and polyDTP2 ( E-g opt = 1.78 eV) are lower than the gaps of poly(dithieno[3,2-b:2',3'-d]pyrrole) N-substituted with alkyl or alkylphenyl groups. This combined with higher IP value yield higher electron affinity (vertical bar EA vertical bar) value. Thus, the obtained new polymers are more difficult to oxidize but easier to reduce as compared to poly(dithieno[3,2-b:2',3'-d]pyrrole)s studied to date. Again, these findings are in a very good agreement with DFT calculations. As evidenced by UV-vis-NIR spectroelectrochemistry, both polymers undergo classical (for conjugated polymers) oxidation, involving the formation of polarons in the first step and bipolarons in the second one. An interesting feature of the oxidation of polyDTP2 is the highly delocalized nature of bipolarons, indicative of the metallic state (featureless absorption tails extending towards NIR part of the spectrum). In order to elucidate the exact nature of the electrochemical oxidation process detailed Raman spectroelectrochemical investigations of polyDTP2 were carried out supported by the vibrational model calculations using two methods: DFT and General Valence Force Field (GVFF). This combined experimental and theoretical study leads to a conclusion that radical cations (polarons) formed at the first stage of oxidation are formed in the pyrrole ring whereas dications formed in the second stage show classical bipolaron configuration with positive charges located on the thiophene rings. (C) 2018 Published by Elsevier Ltd.
|Journal series||Electrochimica Acta, ISSN 0013-4686, (A 40 pkt)|
|Publication size in sheets||0.55|
|Keywords in English||Poly(dithienopyrrole)s; Electropolymerization; UV-vis-NIR spectroelectrochemistry; Raman spectroelectrochemistry|
|Score|| = 40.0, 30-04-2019, ArticleFromJournal|
= 40.0, 11-03-2019, ArticleFromJournal
|Publication indicators||= 1; = 1; : 2017 = 1.101; : 2017 = 5.116 (2) - 2017=4.857 (5)|
|Citation count*||2 (2019-08-03)|
* presented citation count is obtained through Internet information analysis and it is close to the number calculated by the Publish or Perish system.