Role played by chain length and polarity of n-substitutents in electrochromic polymers from the tri-heterocyclic monomer pyrrole-thiophene-pyrrole

Conjugated polymers play an increasingly relevant role in a large number of technological applications (organic solar cells, electrochromic devices, OLEDs). Such preeminence is as much a consequence of their peculiar optoelectronic properties as it is of the possibility to be solution processed. In fact, although unfunctionalized conjugated polymers are almost insoluble, an extensive functionalization with suitable solubilizing chains conveys the required solution processability as well as good adhesion properties with respect to a number of different substrates. The chemical nature (polar, nonpolar) length and branching of the chains do not sizably influence the electronic properties of the polymer, but plays a major role in the solid-state morphology. We here present a systematic study on the role of the solubilizing chains in the overall performances of a series of electropolymerized 2,2′-{thiene-2,5-diylbis[(E)ethene-2,1-diyl]}bis(1H-pyrrole) derivatives. In particular, we show how the nature and length of the chain play a relevant role on the electrochemical behavior of the polymers. Our results can be rationalized in terms of lateral chain induced noncovalent interactions. Finally, the spectroelectrochemical properties of some of these polymers could be of interest for NIR-operating variable optical attenuators.