Qun Ye

Conjugated polymer-based electrochromics: materials, device fabrication and application prospects

The research on electrochromic conjugated polymers (ECPs) and their devices has gone a long way. They can now perform with a multitude of color variations, high optical contrasts, rapid switching speeds and low power consumption. This review traces the progress of color control, synthetic methods, and the development of building blocks for ECPs. The advances in the integration and optimization of electrochromic devices (ECDs) in terms of their constituting components are presented. The potential of ECDs in numerous applications through the illustration of several prototypes is then highlighted. Finally, the challenges associated with the prospective commercialization of the said devices are discussed.

Cubic Polyhedral Oligomeric Silsesquioxane Based Functional Materials: Synthesis, Assembly, and Applications

Organically modified cubic polyhedral oligomeric silsesquioxanes (POSS) have attracted increasing attention in the design of novel functional hybrid materials for applications such as porous materials, liquid crystals, semiconductors, high-temperature lubricants, fuel cells, and lithium batteries. The nanosized POSS moiety can be conveniently modified on the periphery with a variety of functional groups to lead to hybrid materials with desired functions. In addition, suitable mono-functionalized POSS derivatives can be incorporated into polymers as side chains via various synthetic strategies to offer a wide class of functional polymeric materials with tunable physical properties for targeted applications. In this Focus Review, we aim to summarize the recent developments on the chemistry and applications of POSS-based molecules and polymers. Moreover, the properties as well as assembly behavior of the POSS-based functional hybrid materials will be reviewed, and the relationship of the performance of the hybrid materials with the intrinsic nature of the POSS unit will be addressed.

Synthesis of Ultrahighly Electron-Deficient Pyrrolo[3,4-d]pyridazine-5,7-dione by Inverse Electron Demand Diels–Alder Reaction and Its Application as Electrochromic Materials

A new electron acceptor 6-alkylpyrrolo[3,4-d]pyridazine-5,7-dione (PPD) with a very low LUMO level has been synthesized via a challenging inverse electron demand Diels-Alder reaction between thiophene and furan-decorated tetrazine substrates and an electron-deficient 1-alkyl-1H-pyrrole-2,5-dione unit. The PPD monomer has been incorporated into a series of donor-acceptor-type conjugated polymers as electrochromic materials with good optical contrast, fast switching speed, and high coloration efficiency.

Polyhedral oligomeric silsesquioxane-based hybrid materials and their applications

POSS are nano-sized stable 3-dimensional architectures which consist of alternate Si–O bonds to form cage structures with Si atoms as vertices. The mono- or multi-functional POSS could be prepared through modification of their reactive organic functional groups attached in the vertex positions. Depending on the structure and reactivity of those vertex groups, POSS are allowed to be introduced into virtually any existing polymer systems. This review paper summarizes the recent development on the preparation and properties of POSS-containing polymers. In addition, this review paper also gives an overview of the recent development in the area of a wide range of POSS-based composite systems for a variety of applications including fluorescence sensors, liquid crystals, photoresist materials, low dielectric constant materials, organic semiconductors, energy-related materials, drug and gene delivery systems, coating materials and special rubber materials.

Aggregation induced emission based fluorescence pH and temperature sensors: probing polymer interactions in poly(N-isopropyl acrylamide-co-tetra(phenyl)ethene acrylate)/poly(methacrylic acid) interpenetrating polymer networks

Aggregation induced emission (AIE) active copolymers P1–P6 with high molecular weights (14 000–17 000) and low polydispersity indices (1.3–1.4) were prepared through copolymerization of N-isopropyl acrylamide (NIPAM) and tetra(phenyl)ethene (TPE)-based acrylate monomers. Copolymers P1–P6 show comparable thermal stability to poly(N-isopropylacrylamide) (PNIPAM), while their glass transition temperatures are higher by 7–9 °C than those of pristine PNIPAM. Copolymers P1–P6 are soluble in common organic solvents as well as in water. They retain a similar thermal sensitivity to PNIPAM, but their lower critical solution temperatures (LCST) are reduced with increase of TPE content. By changing the molar ratio of P1–P6/poly(methacrylic acid) (PMAA) and pH, complexes P1–P6–PMMA were studied by fluorescence spectroscopy and dynamic light scattering (DLS). The complexes are non-emissive in THF, and their fluorescence can be turned on upon addition of water. Moreover, their fluorescence is enhanced with the decrease in pH values due to the formation of interpenetrating polymer networks (IPNs) through inter-polymer hydrogen bonding. Fluorescence spectroscopy and DLS results also reveal that the phase transition behaviour of IPNs upon heating could be significantly modified by pH change. Reduction in the pH value from 7.0 to 4.0 leads to the decrease in LSCT of IPNs by up to 5 °C with respect to PNIPAM. By tuning the pH value to dissociate the formed inter-polymer hydrogen bonds, the formed IPNs would be able to fold cooperatively to a compact structure without a loss of solubility at temperatures below the LCST. Thus, these novel IPNs with AIE active moieties would be used as drug delivery systems, in which the release process could be readily monitored by fluorescence spectroscopy.

Pyrrolophthalazine dione (PPD)-based donor–acceptor polymers as high performance electrochromic materials

A novel pyrrolophthalazine dione (PPD) acceptor was sophisticatedly designed and synthesized via an inverse electron demand Diels–Alder reaction, followed by aromatization with N-bromosuccinimide. The PPD moiety was incorporated into donor–acceptor type conjugated polymers through Stille coupling polymerization to yield a series of polymers P1–P3 with different linking groups, namely, thiophene, thieno[3,2-b]thiophene, and bithiophene. The polymers reveal excellent solubility in common organic solvents. Due to their low bandgaps of around 1.72–1.78 eV, the polymers show broad absorption that covers most of the visible region. All the polymers reveal electrochromism, switching between dark blue and transmissive sky blue states. In particular, P2 exhibits exceptional electrochromic properties with high optical contrasts of up to 34 and 71% in the visible and NIR regions, high coloration efficiencies of 471 and 651 cm2 C−1 respectively, as well as reasonable switching speeds and good long-term stability.

A thermally stable and reversible microporous hydrogen-bonded organic framework: aggregation induced emission and metal ion-sensing properties

A microporous hydrogen-bonded organic framework (HOF) derived from a polyhedral oligomeric silsesquioxane (POSS) intermediate and an aggregation-induced emission (AIE) luminogen tetraphenylethene (TPE) derivative has been synthesized and structurally characterized by various methods. This unique HOF exhibits a permanent porosity with a Brunauer–Emmett–Teller (BET) surface area of 101.9 m2 g−1. This HOF could be well dispersed in organic solvents in the form of nanoparticles with a size of a few hundred nanometers. These nanoparticles are highly fluorescent in organic solution, and exhibit a high fluorescence quenching selectivity towards copper ions. Furthermore, the fluorescence of this HOF could be recovered by the removal of copper ions upon addition of cyanide and, more interestingly, this process could be repeated several times without considerably sacrificing the sensing activity towards copper ions.

Ultrahigh electron-deficient pyrrolo-acenaphtho-pyridazine-dione based donor–acceptor conjugated polymers for electrochromic applications

Novel electron acceptors 2-alkyl-6,9-di(thiophen-2-yl)-1H-pyridazino[4′,5′:2,3]indeno[6,7,1-def]isoquinoline-1,3(2H)-dione and 2-alkyl-6,9-di(furan-2-yl)-1H-pyridazino[4′,5′:2,3]indeno[6,7,1-def]isoquinoline-1,3(2H)-dione derived from pyrrolo-acenaphtho-pyridazine-diones (PAPD) with a very low-lying lowest unoccupied molecular orbital (LUMO) level have been synthesized via a regioselective inverse electron demand Diels–Alder reaction between thiophene- and furan-substituted 1,2,4,5-tetrazine and an electron-deficient compound 2-(2-alkyl)-1H-indeno[6,7,1-def]isoquinoline-1,3(2H)-dione. The chemical structures of two PAPD monomers were confirmed by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry as well as single-crystal X-ray structural analysis. The time-dependent density functional theory (TD-DFT) calculations were performed to show that PAPD series monomers have a LUMO energy level down to −3.42 eV, much lower than the popular electron acceptors such as benzotriazole, benzothiadiazole and its fluorinated derivatives (−2.19–−2.98 eV). The PAPD based monomer was incorporated into a series of donor–acceptor type conjugated polymers comprising 3,3-bis((dodecyloxy)methyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine and thieno[3,2-b]thiophene as co-monomers through Stille coupling polymerization to give electrochromic conjugated polymers P1–P5 with high number-average molecular weights in the range of 42 000–67 000 (g mol−1). The polymers showed optical bandgaps between 1.90–1.99 eV. Electrochromic devices displayed reversible color changes between purple/red in the neutral state and greyish blue/grey in the oxidized state with an outstanding redox stability of less than 1% decrease in contrast after 800 cycles using polymer P3 as an example, and high optical contrasts of up to 80% at 1500 nm in the near infrared region.

Fluorinated polyhedral oligomeric silsesquioxanes

A series of fluorinated polyhedral oligomeric silsesquioxane (POSS) derivatives were prepared via hydrosilylation reaction and they were characterized by 1H, 13C, 29Si and 19F nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The thermal stability of POSS derivatives was studied using thermogravimetric analysis (TGA) and they exhibited high decomposition temperatures ranging from 327 to 380 °C in air and inert atmosphere. At ambient temperature, fluorinated POSS (FluoroPOSS) compounds 3a–b and 3d–e appear as fluidic oils with a dynamic viscosity of 140–430 mPas and it is noteworthy to mention that 3a, 3d and 3e do not solidify even below −80 °C. The thermal aging experiments of these FluoroPOSS oils were performed, and results revealed that these oils exhibited excellent long-term thermal stability with minimal weight loss over 48 hours in air, rendering them as promising lubricant candidates for unique applications in a wide temperature range from −80 to 300 °C. These fluorinated POSS derivatives have also shown potential in polymer surface modification as evidenced by the great increase in water contact angle from ∼68° for a neat hydrophilic PMMA film to 94–105° for the blended film with 5 wt% fluorinated derivatives. The rise in water contact angle is likely to be due to migration of the hydrophobic POSS core from the interior to the surface, which has been observed by atomic force microscopy (AFM).

Tetraphenylethene (TPE) modified polyhedral oligomeric silsesquioxanes (POSS): unadulterated monomer emission, aggregation-induced emission and nanostructural self-assembly modulated by the flexible spacer between POSS and TPE

Mono-TPE modified POSS molecules, in which the flexible spacers between TPE and POSS moieties control their self-assembly and aggregation, exhibit a unique unadulterated monomer emission in organic solvents as well as an AIE emission in THF/water.