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submitted on 01.10.2019 and posted on 02.10.2019by Yaroslav S. Kochergin, Yu Noda, Ranjit Kulkarni, Klára Škodáková, Ján Tarábek, Johannes Schmidt, Michael J. Bojdys
Fully aromatic, organic polymers have the advantage
of being composed from light, abundant elements, and are hailed as candidates
in electronic and optical devices “beyond silicon”, yet, applications that make
use of their π-conjugated backbone and optical bandgap are lacking outside of
heterogeneous catalysis. Herein, we use a series of sulfur- and
nitrogen-containing porous polymers (SNPs) as real-time optical and electronic
sensors reversibly triggered and re-set by acid and ammonia vapors. Our SNPs
incorporate donor-acceptor and donor-donor motifs in extended networks and
enable us to study the changes in bulk conductivity, optical bandgap, and
fluorescence life-times as a function of π-electron de-/localization in the pristine
and protonated states. Interestingly, we find that protonated donor-acceptor
polymers show a decrease of the optical bandgap by 0.42 eV to 0.76 eV and
longer fluorescence life-times. In contrast, protonation of a donor-donor polymer
does not affect its bandgap; however, it leads to an increase of electrical conductivity
by up to 25-fold and shorter fluorescence life-times. The design strategies
highlighted in this study open new avenues towards useful chemical switches and
sensors based on modular purely organic materials.