Shijie Zhen

Thiadiazolo[3,4-c]pyridine as an Acceptor toward Fast-Switching Green Donor–Acceptor-Type Electrochromic Polymer with Low Bandgap

Thiadiazolo[3,4-c]pyridine (PT), an important analog of benzothiadiazole (BT), has most recently been explored as a novel electron acceptor. It exhibits more electron-accepting ability and other unique properties and potential advantages over BT, thus inspiring us to investigate PT-based donor-acceptor-type (D-A) conjugated polymer in electrochromics. Herein, PT was employed for the rational design of novel donor-acceptor-type systems to yield a neutral green electrochromic polymer poly(4,7-di(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-[1,2,5] thiadiazolo[3,4-c]pyridine) (PEPTE). PEPTE revealed a lower bandgap (Eg,ele=0.85 eV, Eg,opt=1.12 eV) than its BT analog and also favorable redox activity and stability. Furthermore, electrochromic kinetic studies demonstrated that PEPTE displayed higher coloration efficiency than BT analog, good optical memory, and very fast switching time (0.3 s at all three wavelengths), indicating that PT would probably be a promising choice for developing novel neutral green electrochromic polymers by matching with various donor units.

Highly stable hybrid selenophene-3,4-ethylenedioxythiophene as electrically conducting and electrochromic polymers

A family of four novel selenophene–EDOT oligomers were synthesized using Stille coupling and electropolymerized to form highly stable conducting hybrid polymers with excellent electrochromic properties. Structure–property relationships of the oligomers and hybrid polymers, including electrochemical, electronic and optical properties, quantum chemistry calculations and morphology, were systematically explored. The oligomer precursors with planar structures exhibit blue to orange emission characteristics with quantum yields ranging from 1.5 to 9.0%; they may be used as building blocks for the rational design of fluorescent conjugated systems with enhanced main chain planarity. Cyclic voltammetry shows low oxidation potentials ranging from 0.53 to 0.89 V vs. Ag/AgCl, leading to the facile electrodeposition of uniform hybrid polymer films with outstanding electroactivity and stability at low oxidation potentials. The obtained hybrid polymers featured the combined advantages of polyselenophene and PEDOT, such as the lower band gap and better planarity of polyselenophene and the high conductivity, transparency and excellent stability of PEDOT. The hybrid polymers show planar π-conjugated backbones with band gaps ranging from 1.54 to 1.75 eV. They are electrochromic in nature with colour changing from purplish, reddish and saturated blue in the reduced form to transparent sky blue/green upon oxidation. Further kinetic studies demonstrated that the hybrid polymers have decent contrast ratios (22–36%), favourable coloration efficiencies (∼200 cm2 C−1), low switching voltages, fast response time (0.5 s), excellent stability and colour persistence. These materials provide more plentiful electrochromic colours and hold promise for display applications.

Poly(thieno[3,4- b ]-1,4-oxathiane): Medium Effect on Electropolymerization and Electrochromic Performance

The asymmetrical sulfur analog of 3,4-ethylenedioxythiophene (EDOT), thieno[3,4-b]-1,4-oxathiane (EOTT), was synthesized, and its electropolymerization was comparatively investigated by employing different solvent-electrolyte systems (room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6), CH2Cl2-Bu4NPF6, and CH2Cl2-BmimPF6). Further, the effect of solvents and supporting electrolytes on the structure, morphology, electrochemical, electronic, and optical properties and electrochromic performance of the obtained poly(thieno[3,4-b]-1,4-oxathiane) (PEOTT) films were minutely studied. PEOTT film with a band gap (Eg) of about 1.6 eV could be facilely electrodeposited in all the solvent-electrolytes and displayed excellent electroactivity, outstanding redox stability in a wide potential window, and improved thermal stability. Cyclic voltammetry showed that EOTT could be electropolymerized at a lower oxidation potential in BmimPF6 (∼1.0 V vs Ag/AgCl) due to several advantanges of RTIL BmimPF6 itself, such as high intrinsic conductivity and mild chemical conditions, etc., and the resulting PEOTT film exhibited compact morphology with better electroactivity and stability and higher electrical conductivity. On the other hand, PEOTT films from all the sovent-electrolytes also showed the electrochromic nature by color changing from gray blue to green, and further kinetic studies revealed that PEOTT had decent contrast ratios (36%), higher coloration efficiencies (212 cm(2)/C in BmimPF6), low switching voltages, moderate response time (1.2 s), excellent stability, and color persistence. From these results, PEOTT provides more plentiful electrochromic colors and holds promise for display applications.

Molecular design of DBT/DBF hybrid thiophenes π-conjugated systems and comparative study of their electropolymerization and optoelectronic properties: from comonomers to electrochromic polymers

A novel series of comonomers, which comprise dibenzothiophene (DBT) and dibenzofuran (DBF) cores symmetrically linked to thiophene and 3-alkylthiophenes at 2 and 8-positions, were designed and electropolymerized to yield the corresponding electrochromic polymers. The structure–property relationships of comonomers and polymers, including electrochemistry, thermal stability, fluorescence, and electrochromic properties, were systematically explored. In relation to the core group, the alkyl chain group of these polymers had a relatively significant influence on the redox behavior, band gap, neutral state colour, stability, and electrochromic performance (optical contrast, CE, and switching time) of the system. Furthermore, all the polymer films displayed unique electrochromic characteristics with switching the color from yellow to blue. Further kinetic results showed moderate to high optical contrast (20–70%), high colouration efficiency (typically 170–370 cm2 C−1), and favorable switching time (0.8–9.4 s). Among them, the electrochromic performances of 3-hexylthiophene-end-capped polymers were superior to those with thiophene/3-methylthiophene as terminal groups. These results demonstrated that DBT/DBF-based π-conjugated polymer materials hold promise for display applications and DBT/DBF could be further employed for the rational design of excellent electrochromic polymers by matching with other heterocycle units.

Chalcogenodiazolo[3,4-c]pyridine based donor–acceptor–donor polymers for green and near-infrared electrochromics

A series of thiadiazolo[3,4-c]pyridine (PT)/selenadiazolo[3,4-c]pyridine (PSe) in alternation with a variety of thiophenes including thiophene (Th), 3-methylthiophene (MeTh), 3-hexylthiophene (HexTh) and 3,4-ethoxylenedioxythiophene (EDOT) based donor–acceptor–donor (D–A–D) monomers were designed and electropolymerized to yield their corresponding polymers. The structure–property relationships of these monomers/polymers, including band gap, electrochemical behavior, and optical properties, were comparatively investigated. The monomers exhibited orange, red, and purple emission characteristics with quantum yields ranging from 0.072 to 0.849 and could probably be used as building blocks for rational design of fluorescent materials. Also, it was noted that these donor and acceptor units played key roles in optical absorption, leading to neutral electrochromic polymers with different colors including green, purple, gray, sky blue and dark blue. In particular, the obtained EDOT based polymers revealed an obvious color change from green to blue with a faster response time (0.3–0.6 s) relative to their benzochalcogenodiazole analogues. Furthermore, the thiophene and alkyl thiophene-based polymers kept their color constant under different applied voltages and showed superior optical contrast (∼37%) in the near-infrared region compared with that in the visible region. These intriguing features of polymeric materials demonstrated that insertion of chalcogenodiazolo[3,4-c]pyridine into a D–A–D system allowed the formation of green and near-infrared electrochromes.

Synthesis of novel chiral L-leucine grafted PEDOT derivatives with excellent electrochromic performances

Two amino acid-functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives, poly(N-(tert-butoxycarbonyl)-L-leucyl(3,4-ethylenedioxythiophene-2′-yl)methylamide) (PEDOT–Boc–Leu) and poly(L-leucyl(3,4-ethylenedioxythiophene-2′-yl)methylamide) (PEDOT–Leu) were synthesized electrochemically via potentiostatic polymerization of corresponding monomers N-(tert-butoxycarbonyl)L-leucyl(3,4-ethylenedioxythiophene-2′-yl)methylamide (EDOT–Boc–Leu) and L-leucyl(3,4-ethylenedioxythiophene-2′-yl)methylamide (EDOT–Leu), which were synthesized by grafting Boc-L-leucine and L-leucine into a 3,4-ethylenedioxythiophene (EDOT) side chain. The electrochemical behaviors, structural characterization, circular dichroism, spectroscopic properties, surface morphology, electrochromic properties and thermal stabilities of PEDOT–Boc–Leu and PEDOT–Leu films were systematically investigated. These L-leucine grafted PEDOT derivatives displayed excellent reversible redox activities, rough and compact surface, and good thermal stability. The circular dichroism spectra suggested the chirality of these polymers. Importantly, the introduction of the L-leucine group enhanced the electrochromic properties of PEDOT and resulted in high contrast ratios (ΔT% = 49% at 600 nm for PEDOT–Boc–Leu) and high coloration efficiencies (431 cm2 C−1 at 960 nm for PEDOT–Leu). Satisfactory results implied that the obtained polymer films can probably be further developed in various applications, such as electrochromic devices, optical displays and chiral recognition.

Synthesis and electro-optical properties of new conjugated hybrid polymers from EDOT end-capped dibenzothiophene and dibenzofuran

Two novel EDOT end-capped monomers, namely, 2,8-di-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl-dibenzothiophene (DBT-EDOT), and 2,8-di-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl-dibenzofuran (DBF-EDOT), were synthesised via Stille coupling and electropolymerised to form conjugated polymers P(DBT-EDOT) and P(DBF-EDOT). The monomers exhibited blue-light-emitting characteristics, and DFT calculations revealed band gap values of 4.20 eV for DBT-EDOT and 4.34 eV for DBF-EDOT, while those of the corresponding polymers were brought down to 2.46 eV for P(DBT-EDOT) and 2.58 eV for P(DBF-EDOT), respectively. Moreover, both of the polymers displayed good electrochromic properties with colour switching between yellow in the reduced state and purple in the oxidised state. Structure characterisation and properties of monomers and as-formed polymers using FTIR spectroscopy, UV-vis spectroscopy, surface morphology, fluorescence spectroscopy, electrochemistry, and spectroelectrochemistry, together with structure–property relationships, were systematically investigated and comprehensively discussed.

Poly(mono-, bi- or trifuran): effect of oligomer chain length on the electropolymerization performances and polymer properties

Most recently, oligo-/polyfurans have regained widely attention due to their unique properties and promising applications in organic electronics. Herein, to acquire a thorough fundamental understanding of the electrosynthesis and properties of polyfuran (PFu) from different initial oligomers, the synthesis, fluorescence, and electropolymerization performances of α-oligofurans, namely furan (Fu), bifuran (2Fu), trifuran (3Fu), were comprehensively reported and the effect of oligomer chain length on the structure and properties of the resulting PFu films were evaluated. The oligofurans introduced here revealed higher fluorescence efficiency (0.05 for Fu, 0.19 for 2Fu and 0.27 for 3Fu) than the corresponding oligothiophenes and oligoselenophenes. The onset oxidation potential of oligofurans decreased obviously (1.25 V for Fu, 0.8 V for 2Fu, and 0.7 V for 3Fu) with the chain length of the starting monomers increasing, thus leading to the electrodeposition of high quality free-standing PFu films with improved optoelectronic properties. Structure characterization and properties of the as-formed PFu from different initial oligomers, including FT-IR, UV-vis, surface morphology, fluorescence, electroactivity and stability, electrochromic properties, etc., were systematically investigated and comprehensively discussed.

Electrosynthesis and characterization of aminomethyl functionalized PEDOT with electrochromic property

We herein report the electrosynthesis of an aminomethyl functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) derivative, poly(2′-aminomethyl-3,4-ethylenedioxythiophene) (PEDOT-MeNH2), in CH2Cl2-Bu4NPF6 (0.1 mol·L-1) system containing 2% boron trifluoride diethyl etherate (BFEE). The electrochemical behavior, structure characterization, thermal properties and surface morphology of this novel polymer were systematically investigated by cyclic voltammetry (CV), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry (TG) and scanning electron microscopy (SEM), respectively. Electrochemistry results demonstrated that PEDOT-MeNH2 film displayed good redox properties and high electrochemical stability. Besides, PEDOT-MeNH2 films exhibited the electrochromic nature with obvious color changing from purple in the reduced form to blue upon oxidation. By further investigation, kinetic studies revealed that PEDOT-MeNH2 film had decent contrast ratio (41.8%), favorable coloration efficiency (152.1 cm2·C-1), low switching voltages and moderate response time (2.4 s). Satisfactory results implied that the obtained PEDOT-MeNH2 film is a promising optoelectronic material and holds promise for electrochromic devices and display applications.

Electrosynthesis and electrochemical capacitive behavior of a new nitrogen PEDOT analogue-based polymer electrode

In this work, poly(N-methyl-3,4-dihydrothieno[3,4-b][1,4]oxazine) (PMDTO), a new nitrogen poly(3,4-ethylendioxythiophene) (PEDOT) analogue, was synthesized by an electrochemical deposition method, and the capacitive properties of PMDTO were investigated and compared with those of PEDOT. The structure and morphology of PMDTO were characterized by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The pseudocapacitive properties of the as-prepared PMDTO electrodes have been examined by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) measurements and electrochemical impedance spectroscopy (EIS) in 0.1 mol L−1 CH3CN–Bu4NBF4 electrolyte solution. The as-prepared PMDTO electrode showed a high specific capacitance of 154.3 F g−1 at a discharge current density of 3 A g−1 and exhibited cycling stability with the maximal capacitance retention of nearly 71% after 500 cycles at a high current density of 10 A g−1. Additionally, the asymmetrical supercapacitor based on PMDTO and PEDOT electrodes exhibited a maximum specific capacitance of 63.5 F g−1 and an energy density of 12.7 W h kg−1 at a power density of 0.59 kW kg−1. These results implied that the PMDTO electrode can be used as a potential electrode material for supercapacitors.