Aryl-Substituted Buta-1,3-diene and Phenothiazine Based Solid-State Emissive Copolymers: Photophysical Properties and Electrochromic Behaviors

Two phenothiazine-containing aryl-substituted buta-1,3-diene based solid-state emissive copolymers, PTSB and PTSOB, have been designed and synthesized via Suzuki coupling reaction. The twisted aryl-substituted buta-1,3-diene moiety helps to achieve the solid-state emissive nature, whereas redox-active phenothiazine is used for its versatile properties with electrochromic application. The effect of the oxidation state of sulfur (i.e., sulfur is in its lower oxidation state in PTSB, whereas it is in its higher oxidation state in PTSOB) on the optical and electrochemical properties of the copolymer has been investigated. The experimentally obtained higher emission maxima of PTSB (in solution, λ max = 552 nm and in solid state, λ max = 548 nm) compared to PTSOB (in solution, λ max = 472 nm and in solid state, λ max = 509 nm) as well as the band gaps have also been supported by theoretical investigation using DFT. Finally, PTSB has been fabricated as a solid-state electrochromic-electrofluorochromic device operating at a potential window of 0 to 2.5 V. The device shows reversible color change from yellow to dark blue after applying a voltage of 2.5 V with a coloration time ( t c ) = 3.0 s and a bleaching time ( t b ) = 1.9 s with an optical contrast (Δ T ) of 35%. This behavior along with quenching of fluorescence color from yellow to dark by applying a potential suggests its potentiality as an electrochromic-electrofluorochromic polymer.