Electrochemical and optical properties of new electrochromic and fluorescent nitrobenzoyl polypyrrole derivatives

• Synthesis and characterization of new pyrrole monomers. 4″-Nitrobenzoyl (pyrrol-1′-yl)-1-propylate.
• 3″,5″-Dinitrobenzoyl (pyrrol-1′-yl)-1-propylate.
• Chemical and electrochemical polymerization of monomers.
• Electrochemical and spectroelectrochemical characterization of monomers and polymers.
• Empirical calculation of the HOMO and LUMO energies of monomers and polymers fluorescent monomers and polymers.

Two new nitrobenzoyl pyrrole derivatives, 4″-nitrobenzoyl (pyrrole-1′-yl)-1-propylate (NPy) and 3″,5″-dinitrobenzoyl (pyrrole-1′-yl)-1-propylate (DNPy), were synthesized and successfully polymerized by chemical and electrochemical routes. Optical and electrochemical properties of the monomers and polymers were investigated. Both conducting polymers, electrochemically prepared in 0.1 mol L−1 TBABF4/ACN, were deposited onto platinum, glassy carbon or ITO electrodes and showed well-defined reversible redox processes centered around +0.65 V vs. Ag/AgCl (KCl sat.). Cyclic voltammetric studies revealed well adherent films on the electrode surface (Pt, GC, ITO). The polymer films also exhibited electrochromic behavior with color changes from pale green (reduced state) to dark grey (oxidized state), and also a significant absorbance in the infrared region (oxidized state). The monomers and respective polymers are fluorescent, with emission bands at λem = 501 nm for NPy, λem = 515 nm for DNPy and λem = 438 nm for both PNPy and PDNPy, in THF. The monomers also present fluorescence in the solid state. The HOMO and LUMO energy levels were calculated from UV-Vis (λonset) and redox potentials (Ered/oxonset) data.

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