New directly electrosynthesized metal-free copolymeric NIR emitters based on EDOT-[β-thiophene-carboxamide]-fluorene like donor-acceptor systems

Abstract

Three new metal-free copolymeric fluorophores, which present unusual and strong fluorescence NIR emission were synthesized through low-cost, easy, fast and efficient direct electropolymerization methodology without use of expensive catalysts or chemical coupling reactions. The tailoring of these novel more conjugated and polarized molecules was based on the Donor-Acceptor (D-A) approach. The three new designed binary molecular hybrids were obtained by direct oxidative electrocopolymerization with the well-known electron-donating (D) EDOT (3,4-ethylenedioxythiophene) and the electron-acceptor unit (A) ThCO-NHAr. This bis-functionalized molecular block was synthesized between the β-carboxythiophene (ThCO) with electron-donating and fluorescent aromatic amines (naphthylamine (NFT), aminofluorene (FLU) and aminodibenzofuran (DBF)). These monomers were submitted to copolymerization and three novel copolymers – PEDOT-co-2NFT, PEDOT-co-FLU and PEDOT-co-DBF – were prepared and a system block with the general structure [(EDOT)n-(ThCO-NHAr)m] can be proposed. These materials were characterized by infrared spectroscopy, thermogravimetry, ultraviolet-visible absorption, photoluminescence, cyclic voltammetry, photophysical, electrochemical, spectroelectrochemical techniques and scanning electron microscopy. PEDOT-co-2NFT, PEDOT-co-FLU and PEDOT-co-DBF showed higher thermal stability (˜50 °C), more expanded electroactivity range and higher charge accumulation in comparison to PEDOT homopolymer. These new copolymers tailored by D-A approach present very intense emissions in the deep-red and near infrared regions, in solid state and in solution, and they may be applied as novel fluorophores for high efficient deep-red/NIR fluorescent devices.