Aryl-Substituted\nButa-1,3-diene and Phenothiazine\nBased Solid-State Emissive Copolymers: Photophysical Properties and\nElectrochromic Behaviors

Two phenothiazine-containing aryl-substituted buta-1,3-diene\nbased\nsolid-state emissive copolymers, PTSB and PTSOB, have been designed\nand synthesized via Suzuki coupling reaction. The twisted aryl-substituted\nbuta-1,3-diene moiety helps to achieve the solid-state emissive nature,\nwhereas redox-active phenothiazine is used for its versatile properties\nwith electrochromic application. The effect of the oxidation state\nof sulfur (i.e., sulfur is in its lower oxidation state in PTSB, whereas\nit is in its higher oxidation state in PTSOB) on the optical and electrochemical\nproperties of the copolymer has been investigated. The experimentally\nobtained higher emission maxima of PTSB (in solution, λ<sub>max</sub> = 552 nm and in solid state, λ<sub>max</sub> = 548\nnm) compared to PTSOB (in solution, λ<sub>max</sub> = 472 nm\nand in solid state, λ<sub>max</sub> = 509 nm) as well as the\nband gaps have also been supported by theoretical investigation using\nDFT. Finally, PTSB has been fabricated as a solid-state electrochromic-electrofluorochromic\ndevice operating at a potential window of 0 to 2.5 V. The device shows\nreversible color change from yellow to dark blue after applying a\nvoltage of 2.5 V with a coloration time (<i>t</i><sub>c</sub>) = 3.0 s and a bleaching time (<i>t</i><sub>b</sub>) =\n1.9 s with an optical contrast (Δ<i>T</i>) of 35%.\nThis behavior along with quenching of fluorescence color from yellow\nto dark by applying a potential suggests its potentiality as an electrochromic-electrofluorochromic\npolymer.