Microstructural Characterization of Poly(1-hexene) Obtained Using a Nickel α-Keto-β-diimine Initiator

A nickel α-keto-β-diimine initiator (1), when activated with methylaluminoxane (MAO) generates active sites capable of polymerizing α-olefins to high molecular weight products. Herein, we report on the full characterization and detailed microstructural analysis of poly(1-hexene) (PH) homopolymers obtained by using the 1/MAO combination. 13C NMR spectroscopy was used to provide the first qualitative and quantitative determinations of all the sequences in the poly(1-hexene). Such information yields insight into the reactivity of this novel catalytic system

Influence of Steric and Electronic Perturbations on the Polymerization Activities of α-Iminocarboxamide Nickel Complexes

A series of N,O-bound, neutral nickel complexes containing α-iminocarboxamide, η1-CH2Ph, and PMe3 ligands were synthesized to examine the effect of steric and electronic variations at the site adjacent to the imine functionality. These complexes were subsequently activated with Ni(COD)2 for use in ethylene homopolymerization and ethylene/norbornene acetate (NBA) copolymerization reactions. As the bulk of the substituents is increased, one observes a progressive decrease in the rate of ring rotation, a more crowded coordination sphere around nickel, increased monomer consumption activity, and higher molecular weights of the products. Copolymerization reactions showed that the increased crowding around nickel decreases the reactivity of NBA relative to ethylene. As electron density is removed from the metal center, the catalytic species become more active toward ethylene and are more prone to interact with the functionality on NBA

Influence of Steric and Electronic Perturbations on the Polymerization Activities of α-Iminocarboxamide Nickel Complexes

A series of N,O-bound, neutral nickel complexes containing α-iminocarboxamide, η1-CH2Ph, and PMe3 ligands were synthesized to examine the effect of steric and electronic variations at the site adjacent to the imine functionality. These complexes were subsequently activated with Ni(COD)2 for use in ethylene homopolymerization and ethylene/norbornene acetate (NBA) copolymerization reactions. As the bulk of the substituents is increased, one observes a progressive decrease in the rate of ring rotation, a more crowded coordination sphere around nickel, increased monomer consumption activity, and higher molecular weights of the products. Copolymerization reactions showed that the increased crowding around nickel decreases the reactivity of NBA relative to ethylene. As electron density is removed from the metal center, the catalytic species become more active toward ethylene and are more prone to interact with the functionality on NBA

Magnetic Characterization of Open-Shell Donor–Acceptor Conjugated Polymers

Donor–acceptor (DA) conjugated polymers (CPs) with narrow bandgaps and open-shell electronic structures offer a fundamentally new paradigm for integrating the spin degree of freedom within emerging functional devices. Recent advancements have demonstrated that control of long-range electronic correlations enables low-spin (S = 0) and high-spin (S = 1) DA CPs, in which extended π-conjugation overcomes the intrinsic instability of these electronic configurations in light-element materials. While design strategies that articulate mechanisms of spin alignment, topology control, and quantum mechanical exchange are emerging, dedicated studies of the magnetic behavior of these materials remain rare. Here, we utilize sensitive magnetometry techniques to analyze the magnetic properties of open-shell DA CPs with low- and high-spin ground states. We demonstrate improved measurement accuracy through combining vibrating sample magnetometry and superconducting quantum interference device magnetometry. This serves to overcome challenges associated with the inherently weak magnetic moments of these materials and a measurement environment in which the background signal is always significant and must be carefully removed. Analyzing the results following established models for paramagnetic materials enables precise quantification of the spin quantum number and temperature-dependent spin alignment. These studies articulate approaches that enable precise characterization of the bulk magnetic features of these heterogeneous and disordered materials systems, providing a path for rational property elucidation that will enable the integration of these materials within emerging technologies

Light-Induced Trap Reduction in Organic Shortwave Infrared Photodetectors

The distribution of trap states in an organic electronic device plays a critical role in their optoelectronic performance. These traps not only hinder the transport of photogenerated carriers but also cause severe recombination, thus deteriorating the overall photoresponse in the detector. Understanding and eliminating the traps in an organic photodetector is essential to promote and stabilize the response performances. This work examines the effects of trap distribution on the photoresponse performance in a shortwave infrared light detector, by interpreting charge transport dynamics and impedance characteristics. It is found that traps remaining in the device hinder the charge transport and collection in the detector because the traps can serve as recombination centers that deteriorate the photoresponse. The analysis of charge collection efficiency from current–voltage characteristics also validates this hypothesis. A dramatic trap reduction is realized by a proper exposure of the device to high-energy photons, which largely improves and stabilizes the photoresponse of the organic photodiode. It is also observed that the light-induced trap reduction is dependent on the wavelength and light intensity. The findings in this work reveal the fundamental mechanisms in the narrow-bandgap infrared sensing systems, paving the way for practical and stable infrared sensing application settings

New Polyethylene Macroinitiators and Their Subsequent Grafting by Atom Transfer Radical Polymerization

New Polyethylene Macroinitiators and Their Subsequent Grafting by Atom Transfer Radical Polymerizatio

Book reviews RPEiS 40(1), 1978

Digitalizacja i deponowanie archiwalnych zeszytów RPEiS sfinansowane przez MNiSW w ramach realizacji umowy nr 541/P-DUN/201

Solution-Processed Phototransistors Combining Organic Absorber and Charge Transporting Oxide for Visible to Infrared Light Detection

This report demonstrates high-performance infrared phototransistors that use a broad-band absorbing organic bulk heterojunction (BHJ) layer responsive from the visible to the shortwave infrared, from 500 to 1400 nm. The device structure is based on a bilayer transistor channel that decouples charge photogeneration and transport, enabling independent optimization of each process. The organic BHJ layer is improved by incorporating camphor, a highly polarizable additive that increases carrier lifetime. An indium zinc oxide transport layer with high electron mobility is employed for rapid charge transport. As a result, the phototransistors achieve a dynamic range of 127 dB and reach a specific detectivity of 5 × 1012 Jones under a low power illumination of 20 nW/cm2, outperforming commercial germanium photodiodes in the spectral range below 1300 nm. The photodetector metrics are measured with respect to the applied voltage, incident light power, and temporal bandwidth, demonstrating operation at a video-frame rate of 50 Hz. In particular, the frequency and light dependence of the phototransistor characteristics are analyzed to understand the change in photoconductive gain under different working conditions

Tunable Adhesion from Stoichiometry-Controlled and Sequence-Defined Supramolecular Polymers Emerges Hierarchically from Cyanostar-Stabilized Anion–Anion Linkages

Sequence-controlled supramolecular polymers offer new design paradigms for generating stimuli-responsive macromolecules with enhanced functionalities. The dynamic character of supramolecular links present challenges to sequence definition in extended supramolecular macromolecules, and design principles remain nascent. Here, we demonstrate the first example of using stoichiometry-control to specify the monomer sequence in a linear supramolecular polymer by synthesizing both a homopolymer and an alternating copolymer from the same glycol-substituted cyanostar macrocycle and phenylene-linked diphosphate monomers. A 2:1 stoichiometry between macrocycle and diphosphate produces a supramolecular homopolymer of general formula (A)n comprised of repeating units of cyanostar-stabilized phosphate–phosphate dimers. Using a 1:1 stoichiometry, an alternating (AB)n structure is produced with half the phosphate dimers now stabilized by the additional counter cations that emerge hierarchically after forming the stronger cyanostar-stabilized phosphate dimers. These new polymer materials and binding motifs are sufficient to bear normal and shear stress to promote significant and tunable adhesive properties. The homopolymer (A)n, consisting of cyanostar-stabilized anti-electrostatic linkages, shows adhesion strength comparable to commercial superglue formulations based on polycyanoacrylate but is thermally reversible. Unexpectedly, and despite including traditional ionic linkages, the alternating copolymer (AB)n shows weaker adhesion strength more similar to commercial white glue based on poly­(vinyl acetate). Thus, the adhesion properties can be tuned over a wide range by simply controlling the stoichiometric ratio of monomers. This study offers new insight into supramolecular polymers composed of custom-designed anion and receptor monomers and demonstrates the utility of emerging functional materials based on anion–anion linkages

Bias Dependence of Organic-Oxide Phototransistors with Peak Infrared Absorption at 1550 nm

Photodetectors operating across the short-wave infrared region are essential elements of modern optoelectronic technologies. This work demonstrates the integration of an organic bulk heterojunction polymer layer on an oxide thin-film transistor to achieve a peak infrared photoresponse at 1550 nm. As the efficiency of organic semiconductors decreases at longer wavelengths, the phototransistor structure uses trap-assisted charge injection to enhance the photoresponse. This work optimizes the detector performance by investigating the balance between bias stress and signal-to-noise under different bias conditions, enabling a responsivity at 1550 nm up to 130 mA/W at a low light intensity of 2.5 × 10–5 W/cm2