Large-fused-ring-based D-A type electrochromic polymer with magenta/yellowish green/cyan three-color transitions

Large-fused-ring-based conjugated polymers possess wide application prospects in optoelectronic devices due to their high charge transport and wide optical absorption. In this paper, three low-bandgap donor-acceptor (D-A) type polymers PBIT-X (X = 1, 2, 3) based on alkylated benzodithiophene and tris(thienothiophene) as donors and thiadiazol-quinoxaline as an acceptor were synthesized via Stille coupling polymerization at different (donor/acceptor) D/A molar feed ratios. The band gaps of PBIT-1, PBIT-2, PBIT-3 were 1.10 eV, 1.04 eV and 1.02 eV, respectively. Spectroelectrochemistry studies showed that the three D-A type polymers have dual bands located in visible and near-infrared regions in the neutral state. The three D-A type polymers possess good electrochromic properties, such as an optical contrast of 56% and response time of 0.3 s. In particular, PBIT-3 could achieve three color changes from magenta to yellowish green to cyan during the oxidation process. The results indicate that these D-A type conjugated polymers based on large fused-ring units exhibit multiple color changes, endowing them with huge potential applications in visible and near-infrared electrochromic devices.

Electrochemical Synthesis and Electro-Optical Properties of Dibenzothiophene/Thiophene Conjugated Polymers With Stepwise Enhanced Conjugation Lengths

A total of six conjugated polymers, namely PDBT-Th, PDBT-Th:Th, PDBT-2Th, PDBT-Th:2Th, PDBT-2Th:Th, and PDBT-2Th:2Th, consisting of dibenzothiophene, thiophene, and bithiophene were electrochemically synthesized. Their electrochemical and electrochromic properties were investigated in relation to the conjugation chain lengths of the thiophene units in the conjugated backbones. Density functional theory (DFT) calculations showed that longer conjugation lengths resulted in decreased HOMO-LUMO gaps in the polymers. The optical band gaps (E_g,opt) and electrochemical band gaps (E_g,cv) were decreased from PDBT-Th to PDBT-Th:Th, however, PDBT-Th:2Th, PDBT-2Th, PDBT-2Th:Th and PDBT-2Th:2Th displayed the similar band gaps. The conjugation length increments significantly improved the electrochemical stability of the conjugated polymers and exhibited reversible color changes due to the formation of polarons and bipolarons. The results suggest that the conjugated polymers prepared herein are promising candidates for fabricating flexible organic electrochromic devices.

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

A novel triphenylamine derivative-linked ionic liquid unit, 1-(6-((4-(bis(4-(thiophen-2-yl)phenyl)amino)benzoyl)oxy)hexyl)-3-methyl-imidazolium tetrafluoroborate (TTPAC₆IL-BF₄), was designed and synthesized successfully, and its corresponding polymer PTTPAC₆IL-BF₄ was obtained by the electropolymerization method. The highest occupied molecular orbital energy band of TTPAC₆IL-BF₄ is higher and the onset oxidative potential lower compared with that of 6-bromohexyl 4-(bis(4-(thiophen-2-yl)phenyl)amino) benzoate (TTPAC₆Br) without modifying the ionic liquid unit. Both PTTPAC₆IL-BF₄ and PTTPAC₆Br show similar color change and optical contrast under different redox states. However, PTTPAC₆IL-BF₄ presents a faster electrochromic switching time than PTTPAC₆Br owing to the improved ionic conductivity and ion diffusion coefficient with the introduction of a pendent ionic liquid unit. It is more intriguing that PTTPAC₆IL-BF₄ could show electrochromism under different potentials even without supplying any additional electrolyte. The particular behavior further proves that BF₄^- ions around imidazole cations at the side chain may participate in balancing the charge of the polymer backbone when redox reaction happens, resulting in faster movement of ions during the doping process. The results imply that introducing an ionic liquid unit to the side chain is an efficient method to improve the switching time of conjugated polymers and would be inspirational for the design and preparation of novel bifunctional electrochromic polymeric electrolytes.

A Pd-catalyzed optional approach for the synthesis of dibenzothiophenes

A direct and practical approach for the construction of DBTs was developed via a Pd-catalyzed tandem reaction, in which commercially available o-bromo-iodobenzenes combined with benzene thiols or iodobenzenes combined with o-bromo-benzene thiols were applied. These two approaches will provide an alternative for the synthesis of DBT derivatives.

Dibenzofuran and dibenzothiophene based palladium(ii)/NHC catalysts – synthesis and applications in C–C bond formation

In the quest for a new ligand system for Pd(ii)/NHCs, we developed new dibenzofuran and dibenzothiophene based palladium N-heterocyclic carbene catalystsD1–D6in good yields and applied it in C–C bond formation.

Multichromic Polymers Containing Alternating Bi(3-Methoxythiophene) and Triphenylamine Based Units with Para-Protective Substituents

Two novel triphenylamine-based thiophene derivative monomers, 4-cyano-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine and 4-methoxy-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine, were successfully synthesized. The corresponding polymers including poly (4-cyano-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine) and poly (4-methoxy-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine) were electrochemically synthesized and characterized by multiple test method. The electrochemical measurements and spectroelectrochemical analyses revealed that both of the two polymers had quasi-reversible redox behavior and multi-electrochromic properties. The two polymer films showed reversible electrochemical oxidation, excellent optical contrasts in NIR region (62% at 1070 nm for the first polymer, and 86% at 1255 nm for the second polymer), satisfactory coloration efficiencies and fast switching times. The research on the application of the as prepared polymer in the fabrication of electrochromic device was also conducted, employing PCMTPA or PMMTPA as the anodically coloring materials.

Poly(3,4-dioxythiophene) soft nano-network with a compatible ion transporting channel for improved electrochromic performance

A novel nano-soft network of poly(3,4-dioxythiophene) dimer (PM-BTE) was electropolymerized, which greatly promoted electrochromic performance compared with that of PEDOT by a compatible ion transporting channel.