Kaiwen Lin

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.

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 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.

Hybrid π-conjugated polymers from dibenzo pentacyclic centers: precursor design, electrosynthesis and electrochromics

Abstractπ-Conjugated polymers (CPs) represent one of the quite important and rapidly growing branches of flexible electrochromic materials. Electrosynthesized hybrid CPs employing dibenzo pentacycles (fluorenes, carbazoles, dibenzothiophenes, and dibenzofuran) as the backbones have received considerable attention owing to their special structures and interesting electrochromic performances. Recent studies show that polymers from these structures exhibit decent contrast ratios, favorable coloration efficiencies, low switching voltages, fast response time, excellent stability, and color persistence. Intrinsically, their electrochromic properties significantly depend on fine-tailoring of precursor monomer structures, and polymerization techniques and conditions. This review devotes to showing a clear picture of the research progress of dibenzo pentacycle-centered CPs via electrochemical polymerization, including fluorenes, carbazoles, dibenzothiophenes, and dibenzofuran-based hybrid electrochromic polymers. Critical influences of the tailored precursor structures on their electropolymerization and resultant polymer performances are highlighted, aiming at providing an insight for the development of novel fused ring-based polymer electrochromic materials.

[1,2,5]Chalcogenodiazolo[3,4-c]pyridine and selenophene based donor–acceptor–donor electrochromic polymers electrosynthesized from high fluorescent precursors

Conjugated polymers containing selenophene have received attention due to their unique properties and promising application in organic electronics. Herein, to further improve the optoelectronic properties, two typical selenophenes containing [1,2,5]thiadiazolo[3,4-c]pyridine (PT)/[1,2,5]selenadiazolo[3,4-c]pyridine (PS) were synthesized by a donor–acceptor strategy and electropolymerized to form the donor–acceptor–donor polymers. The two precursors exhibited yellow and red emission characteristics with high quantum yields (∼0.48); the value was far greater than those for previously reported selenophenes. Furthermore, electrochromic studies demonstrated that the obtained polymers have superior coloration efficiencies (168 cm−2 C−1) than thiophene based analogues and fast response times (1.6 s).