Electrochromic Properties of Polymers/Copolymers via Electrochemical Polymerization Based on Star-Shaped Thiophene Derivatives with Different Central Cores

Abstract

Three star-shaped thiophene derivatives, namely TPAT, PHT and TPTT with different central cores of triphenylamine, phenyl and 2,4,6-triphenyl-1,3,5-triazine respectively, were synthesized and characterized. They were further successfully prepared into the corresponding cross-linked polymers pTPAT, pPHT and pTPTT via electrochemical polymerization. The cyclic voltammetry curves showed that pPHT and pTPTT displayed the relatively higher onset oxidative potentials than pTPAT. After being applied with the positive voltages in an electrochemical cell, pTPAT exhibited the obvious electrochromic behaviors, while such phenomenons were not observed in the case of pPHT and pTPTT. The theory calculation results together with the electrochemistry properties revealed that the electrochromism of pTPAT may mainly depend on its relatively lower oxidative potential because of the introduction of triphenylamine with low ionization energy. Through the copolymerization with 3,4-ethylenedioxythiophene (EDOT) which is also of relatively low ionization energy, pPHT-EDOT and pTPTT-EDOT both exhibited excellent electrochromic properties. The oxidative potential or ionization energy of polymer is thought to be one of the key factors determining the electrochromism.

An overview on synthetic strategies for the construction of star-shaped molecules

“…Thiophene and bithiophene. Li et al 15 reported the synthesis of 2,4,6-tris(4-(thiophen-2-yl)phenyl)-1,3,5-triazine 298 in 15% yield through cyclotrimerization of 4-(thiophen-2yl)benzonitrile 297 in the presence of CF 3 SO 3 H (Scheme 78). Electropolymerization of 298 resulted in the formation of a polymer of insignicant electrochromic properties.…”

Fast Switching Properties and Ion Diffusion Behavior of Polytriphenylamine Derivative with Pendent Ionic Liquid Unit

“…The onset oxidative potential of TTPAC 6 Br is located at 0.79 V, whereas TTPAC 6 IL-BF 4 shows a lower potential at 0.73 V; the similar oxidative potential is attributed to the introduction of the pendent imidazole group. More importantly, the lower onset oxidative potential indicates an easier electropolymerization process and better electrochromic properties. , Both of them have two pairs of redox peaks: TTPAC 6 Br shows one redox peak at 0.89 and 0.84 V and another at 1.03 and 0.93 V, whereas TTPAC 6 IL-BF 4 shows two pairs of redox peaks at 0.86, 0.83 and 1.04, 0.97 V, respectively. The similar redox peaks of the two monomers are mainly ascribed to the existence of the same redox unit thiophene and triphenylamine.…”

Multi-color electrochromism containing green color based on electrochemically polymerized star-shaped phenyl bithiophene

“…The previously reported 25 research results demonstrated that the relatively lower oxidation potential of pTPAT than pPHT should be attributed to the central core triphenylamine group being of the low ionization energy. 27 Here, the onset oxidative potential of pPHBT was obviously much lower than that of pPHT, which should be attributed to the increased conjugation of the quadruple thiophene group in pPHBT in contrast with bithiophene in pPHT.…”

“…Pd(PPh 3 ) 4 (94.0 mg, 0.08 mmol) was added to the stirred suspension, which was then heated rapidly to 130 1C and maintained under reflux conditions for 4 hours under a nitrogen atmosphere. 25 After cooling to room temperature, deionized water (50 mL) was added to precipitate the main part of the product and then the mixture was washed with water and extracted with dichloromethane consecutively. The product was then dried with MgSO 4 and purified on a silica gel column (petroleum ether-CH 2 Cl 2 5 : 1 as the eluent) to obtain the final product as a white powder (0.38 g, yield 91%).…”

“…The pTPABT polymer film was prepared under the same conditions as those used for pPHBT except for the TPABT monomer, while pTPAT and pPHT were prepared using the previously reported method. 25 Their cyclic voltammetry curves of electrochemical polymerization are shown in Fig. S1 in the ESI.…”