Synthesis of poly-[2,5-di(thiophen-2-yl)-1H-pyrrole] derivatives and the effects of the substituents on their properties

• Three new polymers based on 2,5-di(thiophene-2-yl)-1H-pyrroles (SNS) have been synthesized.
• The properties of the polymer are correlated with substituents attached to their structures.
• The electrical conductivity of the polymers is fair and thermally activated.
• The conductance of the polymers changes under humidity and ammonia exposure.

A series of conducting polymers based on 2,5-di(thiophen-2-yl)-1H-pyrrole (SNS) were synthesized by chemical and electrochemical polymerization of 1-(2-methoxyphenyl)-2,5-di(thiophen-2-yl)-1H-pyrrole 1, 2,5-di(thiophen-2-yl)-1-(o-tolyl)-1H-pyrrole 2 and 1-(2-(2,5-di(thiophen-2-yl)1H-pyrrol-1-yl)phenyl)ethanone 3. The maximum of the UV–visible absorption bands of SNS monomers 1–3 occurred at ∼300 nm. From the cyclic voltammograms (CVs) recorded for the electrochemically polymerized SNS monomers the electrochemical gaps (∼1.3 eV) and HOMO and LUMO energies have been estimated. The UV–visible spectral analysis of polymers revealed electronic transitions corresponding to the π–π* transitions (optical gap of ∼2 eV), and under gap ones in the range of 550–850 nm. FT-IR spectra reveal the coupling of α-H of external thiophene rings during polymerization. The polymers having N-substituted benzene ring with electron donating substituents showed higher electrical conductivity than those with electron withdrawing substituents. The polymers exhibited good thermal stability up to 400 °C (less than 10% loss). The influence of the temperature, humidity and ammonia on the electrical conductivity of the polymers (pressed as pellets) has been also evaluated.