Samenvatting

Materials with semiconducting properties are present in every microelectronic device and form the backbone of our information society. Commonly used inorganic semiconductors are poorly modular and their production is expensive and energetically demanding. Moreover, the use of metals and critical raw materials limits the recyclability of microelectronic components based on inorganic semiconductors and makes them harmful to the environment. Thus, there is a growing importance of finding of new materials with flexible and modular architecture, and based on fully organic, and hence, more environmentally friendly building blocks.
Porous organic π-conjugated polymers (PCPs) are among the most promising candidates and gaining tremendous attention in materials research over the last decade. Due to their fully organic and porous nature, PCPs found the use not only as organic semiconductors, but also as materials for heterogeneous catalysis, gas storage and separation and light emitting or responsive devices. However, it is very hard to predict the optical and electrochemical properties of organic polymers, and theoretical calculations very often contradict with the practical experiments. A common approach to modulate the properties of polymeric frameworks is to extend the π-conjugated system which can lead to increased flexibility and, hence, structural collapse.

Recently, a new class of organic frameworks – sulfur and nitrogen containing porous polymers (SNPs) – was introduced by our research group. SNPs are based on the donor-acceptor polymer concept and combine in their structure electron-deficient triazine-rings (C3N3) and electron-rich thiophene-containing molecular building blocks, enabling intrinsic push-pull effects and enhanced charge-transfer properties. In the present study, it is shown that SNPs can be post-synthetically modified via a rapid and reversible protonation and deprotonation using HCl and ammonia vapors. We show how easily the optical (bandgap) and electrochemical (direct conductivity) properties of prepared materials can be modified without change in the molecular structure. The change of the optical bandgap of SNPs after protonation ranges from 1.82 to 2.09 eV (direct bandgap) and from 1.51 to 1.84 eV (indirect bandgap).

Moreover, the choice of the building blocks also affects the conductivity of the resulting material. The Sulphur-only containing polymer (SNP-S-BTT) showed marked 20-time increase of conductivity after protonation due to higher degree of charge delocalization and more rigid and planar backbone. Furthermore, the synthesised SNPs can be used as naked-eye acid-base sensors because of very rapid and pronounced color change, and also as electrochemical responsive materials.