A yellow to magenta multielectrochromic, pH sensor polymer based on 2,5-di(thienyl)pyrrole modified with methyl orange azo dye

The enhancement of optical contrast and color modulation of π-conjugated polymers may be achieved by incorporating organic dyes through modification of the monomer chemical structure. Methyl orange (MO) azo dye is widely used as a pH indicator, changing its color from orange to red depending on the medium, which makes it a promising strategy to attain polymer materials with innovative optoelectronic properties. A 2,5-di(thienyl)pyrrole (SNS) derivatized with MO, namely SNS-MO has been synthesized with 95% yield and characterized by 1H NMR, 13C NMR, FT-IR and mass spectroscopy techniques. Polymer films of PSNS-MO were electrodeposited onto ITO/glass surface by cyclic voltammetry in (C4H9)4NBF4/CH3CN electrolyte. The PSNS-MO films showed yellow orange color in the neutral state (E = 0.00 V) and light magenta in the oxidized state (E = 0.65 V), presenting chromatic contrast (Δ%T) at 496 and 1010 nm of 14.0 and 23.0, respectively, electrochromic efficiency (η) in the range of 83.90 – 308.10 cm2 C−1 and switching time < 3.5 s. The polymer films were also investigated in Phosphate Buffered Saline (PBS) solutions and after exposure to HCl vapors, in which the color varied from reddish brown at pH = 0.0 to yellowish orange at pH = 4.0. These results show the importance of incorporating azo dyes into the structure of the conjugated polymer to obtain original and advanced materials, since PSNS-MO films are promising for application as active layers in optoelectronic devices and pH optical sensors.