Redox-Active Heteroatom-Functionalized Polyacetylenes

Maleimide Polyacetylene: A Highly Conductive n-Type Polymer

Despite significant interest in conjugated polymers for a wide range of applications in electronics, n-type materials have lagged in performance relative to their p-type counterparts. Polyacetylene is a promising scaffold for addressing this deficiency, as the most conductive conjugated polymer to date when p-doped. However, it displays orders of magnitude lower conductivity in the n-doped state and is not stable under ambient conditions. The systematic introduction of electron-withdrawing groups to the backbone could solve this issue, but few such examples exist. Herein, we address this gap by introducing maleimide polyacetylene (mPA) as a new n-type conjugated polymer. The alternating vinylene-maleimide sequence introduces strongly electron-withdrawing groups to the polyacetylene core while retaining backbone planarity, conferring both ambient stability (LUMO = -4.35 eV) and good conductivity (σ = 22 S/cm) in the n-doped state. The versatile synthetic approach uses ring opening metathesis polymerization to generate nonconjugated precursor polymers with low dispersity and controlled molecular weight. These are then converted to mPA by an unusual base-mediated oxidation that leverages the acidity of the maleimide α-protons.

Electrically Conductive Functional Polymers and Application Progress in Lithium Batteries

Electrically conductive functional polymers (ECFPs) have attracted much attention not only for their electron conductivity but also for their versatile properties, including redox activity, flexibility, and designability. These attributes are expected to enhance the energy density and mechanical compatibility of lithium batteries while mitigating the safety risks associated with such batteries. Furthermore, ECFPs are key candidates as active materials, current collectors, coatings, binders, and additives in energy storage and conversion systems, especially for the development of flexible batteries, dry electrodes, and solid-state batteries. However, their low electron conductivity, poor environmental stability, instability of dopants, and high costs limit their usage in production and large-scale applications. In this review, the two major electrically conductive functional polymer species with conjugated and radical structures are focused on to reveal their conductivity mechanisms. Moreover, the current strategies for improving the performance of these polymers are summarized, which include molecular design to optimize conjugated structures for enhanced conductivity, the addition of hydrophobic groups or protective coatings to improve environmental resistance, a side-chain design that is self-doping to introduce high-stability dopants, and the development of multifunctional systems through compositing with two-dimensional carbon-based materials. Additionally, green processes and renewable resource applications are also introduced with the aim of creating cost-effective and sustainable preparation technologies. The advancement of ECFPs in structural and performance engineering and optimization strategies will facilitate their potentially expansive applications in energy storage and conversion devices.

Cyclic polymers from alkynes: a review

Cyclic polymers have applications across various fields, including material science, biomedicine, and inorganic chemistry. Cyclic polymers derived from alkyne monomers have expanded the application scope to include electronic materials and polyolefins. This review highlights recent advancements in the synthesis of cyclic polymers from both mono- and disubstituted alkynes. The aim is to provide a comprehensive overview of the synthetic methodologies and the application of cyclic polymers derived from alkynes. Additionally, this review will facilitate a comparative analysis of the advantages and limitations of various synthetic methods and describe opportunities for future development of novel catalytic systems to synthesize cyclic polymers from alkynes.

The search for a maximum of the D-π-A paradigm for second order nonlinear optical molecular materials

Push-pull π-conjugated molecules are one of the paradigms of second order nonlinear optical (NLO) materials and have been extensively explored. However, high-performance second order NLO materials with an optimum electron donor (D), π-bridge (π) and acceptor (A) under this paradigm are still the most sought-after. In the present work, D-π-A molecules with optimal D, π and A combination for strong second order NLO properties are proposed based on molecular orbital theories. The optimal D-π-A push-pull molecule achieves an unprecedentedly strong NLO response under the D-π-A paradigm, i.e., the static first hyperpolarizability reaches -453.92 × 10-30 esu per heavy atom using azulene as part of the π-bridge and acceptor to synergistically reinforce the strength of the acceptor. The protocols of D-π-A NLO molecule design through frontier molecular orbital matching of D, π and A with optimal combination of electron donating and accepting strengths shed light on future molecular NLO materials exploration. The simulated two-dimensional second order spectra provide useful information (e.g., sum frequency generation) on the applications of those D-π-A push-pull molecules in nonlinear optics.

Multicomponent Synthesis of Poly(α-aminophosphine chalcogenide)s and Subsequent Depolymerization

Multicomponent reactions of primary phosphines (R-PH2), diimines (R'-N═C(H)-R-(H)C═N-R'), and chalcogens (O2, S8) generate poly(α-aminophosphine chalcogenide)s (4-7) through step-growth polymerization. Characterization of the linear polymers using 31P{1H} diffusion-ordered NMR spectroscopy (DOSY) experiments aided in determining the molecular weight (Mw) of the material. Subjecting the polyphosphine oxide or sulfide to reducing conditions in the presence of a Lewis acid resulted in complete depolymerization of the polymers, quantitatively releasing the 1° phosphine and diimine (2) starting materials, with concomitant reduction of diimine to diamine (9).

Substituent Effects from the Point of View of Energetics and Molecular Geometry in Acene, Polyene, and Polyyne Derivatives

The substituent effect (SE) is one of the most important topics in organic chemistry and related fields, and Hammett constants (σ) are commonly used to describe it. The results of the computational studies carried out for Y-R-X systems (reaction sites Y = NO₂, O^-; substituents X = NO₂, CN, Cl, H, OH, NH₂; spacers R = polyene, polyyne, acene with n = 1-5 repeatable units) show that the substituent properties depend significantly on n, the type of R, and Y. Results of the analysis of the substituent effect stabilization energy and geometrical parameters of the Y-R-X systems reveal that (i) the SE strength and its inductive and resonance components decay with the increase in spacer length, its weakening depends on the Y and R type; quantitative relations describing decay are presented; (ii) the ratio between inductive and resonance effect strength changes with n and depends on Y; (iii) differences in the substituents' properties are examples of reverse SE; (iv) in general, structural parameters are mutually well correlated as well as with the SE descriptors; (v) due to the strong O^- resonance effect, the changes in π-electron delocalization within R are well correlated with the SE strength only for Y = O^- systems.

The Green Box: Selenoviologen-Based Tetracationic Cyclophane for Electrochromism, Host-Guest Interactions, and Visible-Light Photocatalysis

The novel selenoviologen-based tetracationic cyclophanes (green boxes 3 and 5) with rigid electron-deficient cavities are synthesized via S_N2 reactions in two steps. The green boxes exhibit good redox properties, narrow energy gaps, and strong absorption in the visible range (370-470 nm), especially for the green box 5 containing two selenoviologen (SeV²⁺) units. Meanwhile, the femtosecond transient absorption (fs-TA) reveals that the green boxes have a stabilized dicationic biradical, high efficiency of intramolecular charge transfer (ICT), and long-lived charge separation state due to the formation of cyclophane structure. Based on the excellent photophysical and redox properties, the green boxes are applied to electrochromic devices (ECDs) and visible-light-driven hydrogen production with a high H₂ generation rate (34 μmol/h), turnover number (203), and apparent quantum yield (5.33 × 10^-2). In addition, the host-guest recognitions are demonstrated between the green boxes and electron-rich guests (e.g., G1:1-naphthol and G2:platinum(II)-tethered naphthalene) in MeCN through C-H···π and π···π interactions. As a one-component system, the host-guest complexes of green box⊃G2 are successfully applied to visible-light photocatalytic hydrogen production due to the intramolecular electron transfer (IET) between platinum(II) of G2 and SeV²⁺ of the green box, which provides a simplified system for solar energy conversion.

Tweaking the Optoelectronic Properties of S-Doped Polycyclic Aromatic Hydrocarbons by Chemical Oxidation

Peri-thiaxanthenothiaxanthene, an S-doped analog of peri-xanthenoxanthene, is used as a polycyclic aromatic hydrocarbon (PAH) scaffold to tune the molecular semiconductor properties by editing the oxidation state of the S-atoms. Chemical oxidation of peri-thiaxanthenothiaxanthene with H₂ O₂ led to the relevant sulfoxide and sulfone congeners, whereas electrooxidation gave access to sulfonium-type derivatives forming crystalline mixed valence (MV) complexes. These complexes depicted peculiar molecular and solid-state arrangements with face-to-face π-π stacking organization. Photophysical studies showed a widening of the optical bandgap upon progressive oxidation of the S-atoms, with the bis-sulfone derivative displaying the largest value (E₀₀ =2.99 eV). While peri-thiaxanthenothiaxanthene showed reversible oxidation properties, the sulfoxide and sulfone derivatives mainly showed reductive events, corroborating their n-type properties. Electric measurements of single crystals of the MV complexes exhibited a semiconducting behavior with a remarkably high conductivity at room temperature (10^-1 -10^-2  S cm^-1 and 10^-2 -10^-3  S cm^-1 for the O and S derivatives, respectively), one of the highest reported so far. Finally, the electroluminescence properties of the complexes were tested in light-emitting electrochemical cells (LECs), obtaining the first S-doped mid-emitting PAH-based LECs.

Copper-Catalyzed Formal Dehydration Polymerization of Propargylic Alcohols via Cumulene Intermediates

Here we report a copper-catalyzed formal dehydration polymerization of propargylic alcohols. Copper catalysis allows for efficient in situ generation of [n]cumulenes (n = 3, 5) by a soft deprotonation/β-elimination pathway and subsequent polymerization via organocopper species. Alkyne polymers (M_n up to 36.2 kg/mol) were produced with high efficiency (up to 95% yield) and excellent functional group tolerance. One-pot synthesis of semiconducting head-to-head poly(phenylacetylene) was demonstrated through a polymerization-isomerization sequence.