Thiophene-based aldehyde derivatives for functionalizable & adhesive semiconducting polymers

The pursuit for novelty in the field of (bio)electronics demands for new and better performing (semi)conductive materials. Since the discovery of poly(3,4-ethylenedioxythiophene) (PEDOT) – the ubiquitous golden standard – many studies have focused on its applications, but only few on its structural modification and/or functionalization. This lack of structural variety strongly limitsthe versatility of PEDOT, thus hampering the development of novel PEDOT-based materials. In this paper, we present a short and simple strategy for introducing an aldehyde functionality in thiophene-based semiconducting polymers. First, through a two steps synthesis, an EDOT-aldehyde derivative was prepared and polymerized, both chemically and electrochemically. Next, to overcome the inability of thiophene-aldehyde to be polymerized by any means, we synthesized a trimer, in which thiophene-aldehyde is enclosed between two EDOT groups. The successful chemical and electrochemical polymerization of this new trimer is presented. The polymers suspensions were characterized by UV-Vis-NIR spectroscopy, while the corresponding films by FT-IR and four-point-probe (FPP) conductivity measurements. Afterwards, insoluble semiconducting films were formed by using ethylenediamine as crosslinker, demonstrating in this way the suitability of the aldehyde group for the easy chemical modification of our material. The efficient reactivity conferred by aldehyde groups was also exploited for grafting fluorescent polyamine nanoparticles on the films surface, creating a fluorescent semiconducting polymer film. The films prepared by electropolymerization, as shown by means of a sonication test, exhibit strong surface adhesion on pristine indium tin oxide (ITO). This property paves the way for the application of these polymers as conductive electrodes for interfacing with living organisms. Thanks to the high reactivity of the aldehyde group, the aldehyde-bearing thiophene-based polymers prepared herein are extremely valuable for numerous applications requiring the facile incorporation of a functional group on thiophene, such as the functionalization with labile molecules (thermo-, photo- and electro-labile, pH sensitive, etc.).