Synthesis, conductivity and photophysical properties of soluble low bandgap poly{(3-butyryl)pyrrole-[2,5-diyl(p-hydroxybenzylidene)]}

• A soluble low bandgap poly(pyrrolyl methine) was synthesized for the first time.
• The optical bandgap estimated by Tauc equation were 1.15 eV and 1.42 eV, respectively.
• The third-order nonlinear optical susceptibility was in the order of 10−8 esu.

In this paper, a novel soluble low bandgap π-conjugated polymer, poly{(3-butyryl)pyrrole-[2,5-diyl(p-hydroxybenzylidene)]} (PBPDHBE), was synthesized and characterized by 1H NMR, FT-IR, EA and GPC. The glass transition temperature (Tg) of PBPDHBE was found to be 272.11 °C that was about 70 °C larger than that of PBPDHBA. PBPDHBE was decomposed mainly by two steps and the decomposition temperature of backbone chain was up to 467.16 °C. The conductivities of PBPDHBE doped with FeCl3 and H2SO4, were measured to be 8.1 × 10−7 and 6.7 × 10−6 S cm−1, respectively. The absorption peaks of PBPDHBE in NMP solution and film were located at around 462 nm and 482 nm, respectively, and the emission wavelength maximum at 529 nm was also observed. PBPDHBE had a low optical bandgap and the optical bandgap of PBPDHBE film for indirect allowed and direct forbidden transitions were measured to be 1.15 eV and 1.42 eV, respectively. The resonant third-order nonlinear optical susceptibility of PDPBHBE measured by DFWM at 532 nm was in the order of 10−8 esu, which was about 1–3 orders of magnitude larger than that of the other ordinary π-conjugation polymers, because of its low bandgap and the substituent groups on the main chain of PBPDHBE.

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