Yijun Zheng

Stacked-Layer Heterostructure Films of 2D Thiophene Nanosheets and Graphene for High-Rate All-Solid-State Pseudocapacitors with Enhanced Volumetric Capacitance

Stacked-layer heterostructure films of 2D thiophene nanosheets and electrochemically exfoliated graphene are constructed for ultrahigh-rate all-solid-state flexible pseudocapacitors and micro-supercapacitors with superior volumetric capacitance due to the synergetic effect of the ultrathin pseudocapacitive thiophene nanosheets and the capacitive electrochemically exfoliated graphene.

Efficient Synthesis and Properties of Novel Near-Infrared Electrochromic Anthraquinone Imides

An efficient synthesis of novel near-infrared electrochromic 6-substituted (NO2, Br) anthraquinone imides, i.e., 2a and 2b, was established. Bearing functional groups suitable for further structural modifications by nucleophilic substitution reaction and various metal-catalyzed coupling reactions (e.g., Suzuki coupling), 2a and 2b were easily transferred to 1a by reaction with 4-methoxyphenol and 1b by reaction with 4-hexyloxyphenylboronic acid, respectively. These new imides are electrochromic and absorb intensely in the near-infrared range of 700-1600 nm upon electrochemical reduction.

Near-infrared electrochromic and chiroptical switching polymers: synthesis and characterization of helical poly(N-propargylamides) carrying anthraquinone imide moieties in side chains

Optically active poly(N-propargylamides) containing chiral anthraquinone imide (AQI) side groups have been synthesized. The chiroptical and electrochromic properties of the polymers are investigated. The polymers exhibit intense Cotton effects in the absorption regions of both main- and side-chains, strongly suggesting a helical conformation of the polymer backbone and a skewed packing of pendant chromophores. Additionally, the polymers show two reversible redox states (radical anion and dianion). Intense circular dichroism (CD) signals centered at 780 nm and 530 nm are assigned to the radical anion and dianion intermediates, respectively. The voltage-controlled reversible Cotton effects demonstrate the newly synthesized AQI-containing poly(N-propargylamides) as potential electrochemically driven chiroptical switching materials that operate in the near-infrared wavelength region.

Synthesis and characterization of a novel kind of near-infrared electrochromic polymers containing an anthraquinone imide group and ionic moieties†

A novel near-infrared (NIR) electrochromic polyelectrolyte consisting of anthraquinone imide (AQI) pendants and a poly(1-vinylimidazole bromide) main chain was synthesized viaradical polymerization. Its AQI content was varied by copolymerization with 1-vinyl-3-butylimidazole bromide to improve the processability of the polymer as well as the monomer conversion. The electrochemical and electrochromic properties of both homopolymer and copolymers were investigated. All the (co)polymers exhibited two reversible redox states (radical anions and dianions). Spectroelectrochemical analysis in solution showed that the radical anions possessed intense NIR absorptions with λmax values in the range 820 to 830 nm, while the dianions exhibited absorptions between 460 and 560 nm. The homopolymer film displayed an optical attenuation of 3 dB/µm at 810 nm with a switching time of 20 s. Such a polymer can change color in a single film device without any additional electrolytes and showed a rapid response time of 1 s at 810 nm.

Optically active helical vinylbiphenyl polymers with reversible thermally induced stereomutation

A series of novel chiral vinylbiphenyl monomers, (+)-2-[(S)-alkoxycarbonyl]-5-(4′-hexyloxyphenyl)styrene (S-(+)-I-Mm, m = 0, 1, 2, 3)/(−)-2-[(R)-sec-butyloxycarbonyl]-5-(4′-hexyloxyphenyl)styrene (R-(−)-I-M0), were designed and synthesized to search for new building blocks of optically active helical polymers. They were converted to the corresponding polymers, S-(+)-I-Pm/R-(−)-I-P0, via radical polymerization. The polymers display chiroptical properties obviously distinct from those of the monomers. The specific optical rotation of S-(+)-I-P0 scales up with molecular weight at the beginning and then levels off. The prefactor (ρ = Rg/Rh) of S-(+)-I-P0 in tetrahydrofuran at 30 °C is 2.38, indicating a stiffened polymer main chain. Changing the configuration of the stereocenter in the chiral tails as in S-(+)-I-M0/R-(−)-I-M0 leads to an inversion of optical rotation for both monomers and polymers. These results suggest that the biphenyl pendants are able to drive a polyethylene backbone to adopt an extended helical conformation, the twist sense of which is governed by the chiral tails of pendants. When the stereocenter goes far away from the polymer backbone, the optical rotation strength of polymers becomes weakened, implying the reduced asymmetric coupling between the polymer backbone and the chiral pendant groups. Unlike the previously reported helical vinylterphenyl polymers, the sign of optical rotation of S-(+)-I-Pm does not alternate with the variation of the distance between the stereocenter and the polymer backbone. It is probably attributed to the direct connection of the chiral alkoxycarbonyl group to the polymer backbone due to the absence of a rigid spacer. Such a small structural modification also endows the polymers with the dynamic nature of helical conformation, as implied by the reversible thermally induced stereomutation of polymers in aromatic solvents and the relatively lower glass transition temperature compared with their terphenyl-based counterparts.

Visible and near-infrared chiroptical gels containing electrochromic anthraquinone imide groups

A cholesterol-based organogelator bearing an anthraquinone imide (AQI) group was synthesized and characterized. It self-assembled into chiral gels in acetonitrile at low concentrations, which displayed a combination of electrochromic and chiroptical properties. Upon electrochemical reduction at −700 mV, the gel exhibited new absorption bands at around 820 nm corresponding to π*-π* (SOMO→LUMO) transitions of the radical anion of AQI and strong negative Cotton effects in the same spectral region. With further reduction at −1000 mV, a new CD band with a negative Cotton effect in the range from 500 nm to 800 nm appeared concomitant with the variation of absorption spectrum. Thus, with the use of electrochromic AQI chromophore as a switch-responsive unit and the stable gel of compound N-[3β-cholest-5-en-3-yl N-(2-aminoethyl) carbamate] anthraquinone-2,3-dicarboxylic imide as a chiral scaffold, a redox-triggered chiroptical switch operating in visible and near-infrared region was realized.

Electrochemically Durable Thiophene Alkanethiol Self-Assembled Monolayers

Thiophene-based redox-active self-assembled monolayers (SAMs) were prepared on gold substrates. The alkanethiol derivatives of 1TPh-OC12SH and ETPh-OC12SH contain thiophene (1T) and 3,4-ethylenedioxythiophene (ET) units, respectively, with unprotected (nonsubstituted) thiophene α-carbons. PhETPh-OC12SH contains the ET unit, and all thiophene carbons are protected. Using these thiophene alkanethiol derivatives, we characterized the effect of thiophene carbon protection on the redox behavior of the thiophene SAMs by cyclic voltammetry. The formation of SAMs was confirmed by X-ray photoelectron spectroscopy and reflective IR. The IR peaks in the fingerprint region were assigned with the help of DFT calculations. Although 1TPh-OC12SH and ETPh-OC12SH SAMs lost their electrochemical activity during the first anodic scan, PhETPh-OC12SH SAMs are stable and maintain their electrochemical activity for at least 1200 redox cycles.