Preparação e caracterização espectroscópica de copolímeros eletrocrômicos e fluorescentes derivados de pirrol e oligômeros de tiofeno para aplicação em dispositivos eletrocrômicos e diodos emissores de luz orgânicos (OLEDs)

Abstract

The copolymerization of the monomers 3,3’” Dihexyl-2,2’:5’,2″:5″,2’″-quaterthiophene (DQT) and (R)-(-)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-α-phenylglycinate (DNBP), as well as the 2,2′:5′,2′′-terthiophene (TTF) and DNBP was successfully achieved by electrochemical techniques. Poly(DQT), poly(TTF), poly(DNBP), poly(DQT-co-DNBP) and poly(TTF-co-DNBP) films were characterized by infrared spectroscopy, Scanning Electron Microscopy (SEM), spectroelectrochemical and fluorescence spectroscopy techniques. The infrared spectroscopy confirmed the presence of the main functional groups of the homopolymers. The two copolymers obtained in feed ratio showed morphologies their precursor polymers. It was observed, for all copolymers reversible changes in the color of the films during the electrochemical characterization by cyclic voltammetry, the films of poly(DQT-co-DNBP) showed changes from yellow or orange in the reduced state to green or blue in the state oxidized, but this dependent on the proportion of the comonomers. All films of poly(TTF-co-DNBP) exhibited color changes from orange to brown in the reduced state in the oxidized state. These changes are more significant in the films of poly(DQT-co-DNBP) deposited with 1:5 feed ratio and poly(TTF-co-DNBP) deposited with 1:8 feed ratio, as shown by the track of the CIE 1931 xy chromaticity coordinates and by the electrochromic parameters. The films of poly(DQT-co-DNBP) in the ratio 1:5 (thickness 0.8 ± 0.2 µm) presented chromatic contrast (ΔT%) at 660 nm of 62 %, coulombic efficiency of 48 %, electrochromic efficiency (η) ~ 230 C cm-2 and redox stability (ΔT% = 17% in λ = 660 nm at the 1000th cycle). While the films of poly(TTF-co-DNBP) in the ratio 1: 8 (thickness 1.0 ± 0.2 µm) presented a coulombic efficiency of approximately 81 %, chromatic contrast on the order of 48 % in λ = 1065 nm and coloration efficiency in the range of 180 C cm-2 with good stability up to 700 cycles of charging / discharging. Solutions of poly(DQT) and poly(TTF) its copolymers with DNBP (independently of the feed ratio) in N-methylpyrrolidone (NMP) are fluorescente. The copolymers of poly(DQT-co-DNBP) have emission bands at 555 and 585 nm when excited at 375 nm and copolymers of poly(TTF-co-DNBP) emit at 516 and 548 nm when excited at 450 nm. Therefore, these polymers are promising as materials having fluorescent and electrochromic properties and may be applied as an active layer for optoelectronic devices such as OLEDs and electrochromic devices.