Synthesis and fluorescence properties of a soluble polypyrrole derivative based on a dipyrrole monomer

A unique dipyrrole monomer 2-methyl-1,3-di(1H-pyrrol-1-yl)propan-1-one (MDPP) was synthesized and the corresponding branched polymer (PMDPP) with the molecular weight (Mw) of 2416 was obtained by the chemical polymerization. The molecular structures of MDPP and PMDPP were characterized by FTIR and NMR. It was found that the polymerization of MDPP was accomplished on the pyrrole ring which is attached to the carbonyl group. The resulting polymer had an amorphous structure and could be dissolved in many organic solvents. The fluorescence measurements were carried out on PMDPP solutions, which emitted the green light in the range of 556–574 nm under the excitation of 467 nm depending on the solvents. It is interesting that the Stokes shift of the PMDPP solution was more sensitive to the electron donor–acceptor properties of solvent rather than the polarity of solvent. Notably, the maximum emission wavelength ( λ max em ) of the PMDPP solution showed a red shift from 556 nm to 586 nm with the increase of PMDPP concentration from 1.80 × E−5 g/ml to 6.314 × E−4 g/ml in THF, and it exhibited a remarkable dependence on the excitation wavelength in the range of 327–507 nm, which led to a gradual red shift of the λ max em from 510 nm to 584 nm.