A Conjugated Copolymer Bearing Imidazolium-based Ionic Liquid:Electrochemical Synthesis and Electrochromic Properties

An imidazolium-based ionic liquid(IL)modified triphenylamine derivative,namely 1-(4-((4-(diphenylamino)benzoyl)oxy)butyl)-3-methyl imidazole tetrafluoroborate(TPAC_(6)IL-BF_(4)),was designed and synthesized,and further applied with 3,4-ethylene dioxythiophene(EDOT)to prepare conjugated copolymer P(EDOT:TPAC_(6)IL-BF_(4)) via electrochemical polymerization.The cyclic voltammetry curves show that the copolymer P(EDOT:TPAC_(6)IL-BF_(4))possesses two pairs of redox peaks,which should be ascribed to the redox behaviors of EDOT and triphenylamine.The ultraviolet-visible(UV-Vis)absorption spectrum of P(EDOT:TPAC_(6)IL-BF_(4))exhibits one maximum absorption peak at 580 nm and a small shoulder characteristic peak at 385 nm under neutral state which are assigned toπ-π^(*)conjugated structure of EDOT and triphenylamine.After being applied at the positive voltage,the copolymer color changes from dark blue to light blue,which is close to the color of poly(3,4-ethylenedioxythiophene)(PEDOT).Surprisingly,the copolymer P(EDOT:TPAC_(6)IL-BF_(4))shows shorter switching time of 0.37 s,0.30 s at 580 nm and 0.38 s,0.45 s at 1100 nm compared with PEDOT.It is more intriguing that the copolymer P(EDOT:TPAC_(6)IL-BF_(4))exhibits electrochromism even in free supporting electrolyte.The results confirm that the existence of imidazolium-based ionic liquid has an improvement on the ion diffusion properties and the switching time of conjugated polymer,which may provide a potential direction for the preparation of high-performance electrochromic materials.

Large magnetic refrigerant capacity of HoFe_(1-x)Co_(x)Al(x=0,0.3)compounds

Magnetic and magnetocaloric properties of HoFe_(1-x)Co_(x)Al(x = 0, 0.3) were investigated. Both HoFeAl and HoFe_(0.7)Co_(0.3) Al undergo a second-order ferromagnetic(FIM) to paramagnetic(PM) transition at Curie temperatures(TC) of 87 and 82 K, respectively. The magnetocaloric effect is improved by the introduction of Co in HoFeAl compound. For a field change from 0 to 5 T,the maximum values of magnetic entropy change(﹣△SM)are 7.0 J·kg^(-1)·K^(-1) for HoFeAl and 8.6 J·kg^(-1)·K^(-1) for HoFe_(0.7)Co_(0.3) Al. In addition, the refrigerant capacity(RC)is enhanced largely from 416.2 J·kg^(-1) for HoFeAl to561.9 J·kg^(-1) for HoFe_(0.7)Co_(0.3) Al. This large RC is attributed to the large ﹣?SM and the wide temperature span of ?SM peak in HoFe_(0.7)Co_(0.3) Al compound. The physical mechanism of improvement in magnetocaloric effect by Co substitution in HoFeAl was also discussed in detail.