Study On The Synthesis And Performance Of Triarylamine-containing Polyurethane Electrochromic Materials

Electrochromism(EC)can be defined as a reversible and visible change in the transmittance and/or reflectance of a material by applying different voltages or electric currents with the result of electrochemical oxidation or reduction.Electrochromic materials(ECMs)exhibit a reversible optical change in absorption or transmittance upon being electrochemically oxidized or reduced.Organic electrochromic materials have become the most hotspot owing to the advantages,such as fast response rate,variable color,facile synthesis,simple molecular design and low cost.ECM has extensive and potential application in many fileds.In this paper,we have synthesized a series of polyurethanes(PU)based on the reaction of N,N-bis(4-isocyanatophenyl)aniline(M1),N,N-bis(4-phenylisocya-nate)-4-N'-carbazole-1,4-aniline(M2),N,N-bis(4-phenylisocyanate)-N',N'-carbazol-yl-1,4-phenylenediamine(M3),N',N'-bis(a-naphthyl)-N,N'-bis(4-phenylisocyanate)biphenyl(M4)and N,N'-diphenyl-N,N'-bis(4-phenylisocyanate)biphenyl(M5)wit-h double hydroxyl compounds phenolphthalein(a),bisphenol A(b),4,4'-dihydro-xybiphenyl(c),4,4'-bishydroxybenzophenone(d)and bisphenolfluorene(e),respec-tively.The PUs contain triarylamine group and show good electrochromic charac-teristics.The structures of the polymers were investigated by infrared spectrosco-py(FT-IR)and hydrogen nuclear magnetic resonance(1H NMR);and the thermo-stability and morphology were studied by thermogravimetric analysis(TGA)and scanning electron microscope(SEM).The molecular weight was measured by g-el permeation chromatography(GPC).The polymers were coated onto ITO and the electrochromic property was investigated by using the UV-Vis absorption spectra(UV-vis)and cyclic voltammetry(CV).The polymer exhibited good film forming and mechanical property.The polymer films revealed excellent stability of the electrochromic characteristics by continuous cyclic scans between 0 V and 1.6 V,with a color changing from neutral pale yellowish to a blue doped form at applied potentials.The highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)energy levels of these polymers were determined by CV method consistent with the results of quantum chemical calculation.Based on above all,our materials can be used as ECMs.The UV absorption of PU exhibited strong absorption at 314-1034nm,and the thermal decomposition temp of the films was above 200?,the number-average molecular weight(Mn)was determined as 8417-20398.The properties prove that the PUs are multipurpose materials which will be subject of application in hole-transporting,ECMs,chemical sensor in near future.