Synthesis and characterization of fluorescent nitrobenzoyl polythiophenes

Highlights: • Synthesis and characterization of fluorescent thiophene derivatives. • 4"-nitrobenzoyl (thiophene-3′-yl)-1-ethylate monomer and polymer. • 3",5"-dinitrobenzoyl (thiophene-3′-yl)-1-ethylate monomer and polymer. • Chemical and electrochemical polymerization of monomers. • Empirical calculation of the HOMO and LUMO energies of monomers and polymers. - Abstract: Two thiophene derivatives named 4"-nitrobenzoyl (thiophene-3′-yl)-1-ethylate (NTh) and 3",5"-dinitrobenzoyl (thiophene-3′-yl)-1-ethylate (DNTh) were synthesized and characterized. Both monomers were electrochemically polymerized onto platinum or glassy carbon electrodes by potentiodynamic method in 0.1 mol L⁻¹ TBABF₄/CH₂Cl + boron trifluoride diethyl etherate (BFEE) (1:1, v/v). These monomers were also successfully polymerized by chemical oxidation using FeCl₃/CHCl₃. Spectroscopic and electrochemical properties of the monomers and polymers were investigated. Films of both polymers showed well-defined reversible redox system at the anodic branch (1.0 V vs. Ag/AgCl, KCl (sat.)), attributed to thiophene doping/dedoping process; and another redox process at the cathodic branch (PNTh) (or two redox processes for PDNTh) was attributed to the reduction of the 4-nitrobenzoyl or 3,5-dinitrobenzoyl substituent groups. The THF solutions of monomers and polymers are fluorescent, with emission bands at λ_max = 488 nm (NTh), 511 nm (DNTh), 440 nm (PNTh) and 546 nm (PDNTh). The monomers are also fluorescent in the solid state.