Doping behaviour of electrochemically generated model bithiophene meta-substituted star shaped oligomer

• Tris(bithiophene) meta-substituted benzene dimerises upon electrooxidation.
• The insoluble dimer features well developed electrochromic properties.
• Unreacted bithiophene groups activate during dimer doping.
• Reactivity of bithiophene groups narrows down the dimer's stable doping range.
• The paradox of concurrent dimer formation and overoxidation is disclosed.

The redox processes accompanying electrochemical oxidation of 1,3,5-tris(bithiophene)benzene (6TPh) and its products have been investigated using a suite of spectroelectrochemical tools. Investigated tri-functional molecule, featuring reactive bithiophene units can be considered a model of numerous star shaped compounds – the building blocks of dense π-conjugated polymer networks. Accounting for conjugation disruption between the meta-arranged bithiophene groups, it is found that electrochromic films generated upon 6TPh electrooxidation comprise primarily dimers (6TPh)2, whose α,ω-diphenylquaterthiophene units are the principal redox doping active species. Upon reaching a certain, electrochemically inconspicuous oxidation threshold, profound changes take place in the oligomer film, incurring irreversible changes to its electroactive properties, previously observed for these systems. An attempt is made to examine the nature of these changes and the impact they have on the doping behaviour of this intriguing π-conjugated system.

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