Síntese e caracterização de novos polímeros z-conjugados baseados em derivados de poli(2,5-di(2-tienil)pirrol) (PSNS) e polipirrol (PPY) com propriedades eletrocrômicas

Abstract

Electrochromic conjugated polymers may have high potential for application as optically active layers in optoelectronic devices due to their high optical contrast, low response time, greater processability and electrochromism. These properties can be manipulated through modifications in the structure of their monomers/polymers, which can be achieved by inserting different substituents with electron donating group (EDG) and/or electro-withdrawing groups. Among the methodologies described in the literature for modifying these monomers, it’s highlighted, in particular, the synthesis of pyrrole (Py) and 2,5-di(2-thienyl)pyrrole (SNS) derivatives due to the good optical properties of their conjugated polymers. In this work, three new monomers derived from pyrrole and SNS were synthesized in high yields: 2-(2,5- di(thiophen-2-yl)-1H-pyrrol-1-yl)ethyl)-2-oxo-2H-chromene-3-carboxamide (SNS-CM), 7-(3- (1H-pyrrol-1-yl)propoxy)-3H-phenoxazin-3-one (PY-RES) and (E)-3-(4-(1H-pyrrol-1- yl)phenyl)-1-(4-(dimethylamino)phenyl)prop-2-en-1-one (PY-CHA). The PSNS-CM and PPY-RES films were obtained through electrochemical polymerization using cyclic voltammetry. The monomers were subjected to electrochemical copolymerization in the presence of EDOT, in which the copolymers PSNS-CM-EDOT-co-EDOT, PPY-RES-coEDOT and PPY-CHA-co-EDOT were obtained. While the PSNS-CM film showed a reversible color change from yellow in the reduced state to blue-gray in the oxidized state, its copolymer in the 1:5 ratio (SNS:EDOT) showed a wider color variation (purple, red, orange, yellow, green and blue). The PPY-RES-co-EDOT copolymer showed a mustard yellow coloration in the reduced state and orange in more oxidized states. Although the PPY-CHA film was not formed on the ITO surface, its copolymer was obtained, and showed a reversible color change between its reduced and oxidized states (purple, red, orange, yellow, green and blue). The color changes of all films were also represented by CIE 1931 color coordinates. The polymeric films demonstrated transmittance variation ranging from 6.37% (420 nm) to 46.01% (938 nm), coulombic efficiency between 27% and 98.70%, and electrochromic efficiency between 61.27 cm2 C -1 and 164.8 cm2 C -1 . The films were subjected to redox cycle analyses, in which the copolymers presented better stability after 500º cycles. Comparing these values with the data of their homopolymers (PSNS-CM, PPY-RES and PPY-CHA), the copolymers presented better electrochromic properties (transmittance variation, coulombic efficiency and electrochromic efficiency). Thus, the PSNS-CM-co-EDOT copolymer in a 1:5 ratio was used to assemble two electrochromic devices: in the first (DEC1), the copolymer was utilized as the electrochromic electrode and PEDOT as the secondary electrode; in the second (DEC2), it was employed the copolymer as the electrochromic electrode and a ITO free of deposited film. DEC1 showed a reversible color change between green and blue, while DEC2, between purple, yellow and green. Thus, the results suggest that the electrochromic films obtained in this work are promising for application as an active layer in optoelectronic devices such as smart windows.