Kumada catalyst transfer polymerization (KCTP) has been widely adopted to synthesize π-conjugated polymers for various electronic and biological applications. However, the scope of monomers that can ...be polymerized with control is generally limited to small electron-rich (hetero)cycles. Because control over polymer molecular weight, dispersity, and end-groups is intrinsically linked to intramolecular catalyst transfer, improved catalysts are necessary to broaden the scope of this important polymerization technique. In this study, we present a computational investigation of how ligand bite angle, steric substituent effects, and electronic substituent effects of Ni(phosphine) catalysts influence KCTP. Density functional theory is utilized to model the catalytic cycle, and catalyst design rules are proposed based on how specific ligand variations individually and cooperatively affect the fundamental steps of oxidative addition, transmetalation, reductive elimination, and ring walking. Recommendations are made for developing new catalysts to enhance ring walking (and hence control the polymerization) for challenging π-conjugated monomers. For example, bulky monomers should be polymerized by using sterically unencumbered and electron-withdrawing ligands, and electron-deficient monomers should be polymerized by using electron-donating sterically bulky ligands. These results are important because they can be used to design a new generation of catalysts to expand the scope of π-conjugated polymers that can be prepared in a controlled manner.
Hybrid organic–inorganic perovskites (HOIPs) have garnered widespread interest, yet stability remains a critical issue that limits their further application. Compared to their three-dimensional (3D) ...counterparts, two-dimensional (2D)-HOIPs exhibit improved stability. 2D-HOIPs are also appealing because their structural and optical properties can be tuned according to the choice of organic ligand, with monovalent or divalent ligands forming Ruddlesden–Popper (RP) or Dion–Jacobson (DJ)-type 2D perovskites, respectively. Unlike RP-type 2D perovskites, DJ-type 2D perovskites do not contain a van der Waals gap between the 2D layers, leading to improved stability. However, bifunctional organic ligands currently used to develop DJ-type 2D perovskites are limited to commercially available aliphatic and single-ring aromatic ammonium cations. Large conjugated organic ligands are in demand for their semiconducting properties and their potential to improve materials stability further. In this manuscript, we report the design and synthesis of a new set of larger conjugated diamine ligands and their incorporation into DJ-type 2D perovskites. Compared with analogous RP-type 2D perovskites, DJ 2D perovskites reported here show blue-shifted, narrower emissions and significantly improved stability. By changing the structure of rings (benzene vs thiophene) and substituents, we develop structure–property relationships, finding that fluorine substitution enhances crystallinity. Single-crystal structure analysis and density functional theory calculations indicate that these changes are due to strong electrostatic interactions between the organic templates and inorganic layers as well as the rigid backbone and strong π–π interaction between the organic ligands themselves. These results illustrate that targeted engineering of the diamine ligands can enhance the stability of DJ-type 2D perovskites.
Perylene diimides (PDIs) are one of the most widely studied n‐type materials, showing great promise as electron acceptors in organic photovoltaic devices and as electron transport materials in ...n‐channel organic field effect transistors. Amongst the well‐established chemical modification strategies for increasing the electron mobility of PDI, substitution of the imide oxygen atoms with sulfur, known as thionation, has remained largely unexplored. In this work, it is demonstrated that thionation is a highly effective means of enhancing the electron mobility of a bis‐N‐alkylated PDI derivative. Successive oxygen–sulfur substitution increases the electron mobility such that the fully thionated derivative (S4) has an average mobility of 0.16 cm2 V−1 s−1. This is two orders of magnitude larger than the nonthionated parent compound (P), and is achieved by solution deposition and without thermal or solvent vapor annealing. A combination of atomic force microscopy and 2D wide angle X‐ray scattering experiments, together with theoretical modeling of charge transport efficiency, is used to explain the strong positive correlation observed between electron mobility and degree of thionation. This work establishes thionation as a highly effective means of enhancing the electron mobility of PDI, and provides motivation for the development of thionated PDI derivatives for organic electronics applications.
The effect of oxygen–sulfur atomic substitution (thionation) on the electron mobility of perylene diimide is investigated. Electron mobility correlates with the extent of thionation, with the highest mobilities obtained in solution processed nonannealed devices. This work shows that thionation is a promising strategy for boosting the electron mobility of perylene diimide derivatives.
Singlet fission is a process that splits collective excitations, or excitons, into two with unity efficiency. This exciton splitting process, unique to molecular photophysics, has the potential to ...considerably improve the efficiency of optoelectronic devices through more efficient light harvesting. While the first step of singlet fission has been characterized in great detail, subsequent steps critical to achieving overall highly-efficient singlet-to-triplet conversion are only just beginning to become well understood. One of the most elementary suggestions, which has yet to be tested, is that an appropriately balanced coupling is necessary to ensure overall highly efficient singlet fission; that is, the coupling needs to be strong enough so that the first step is fast and efficient, yet weak enough to ensure the independent behavior of the resultant triplets. In this work, we show how high overall singlet-to-triplet conversion efficiencies can be achieved in singlet fission by ensuring that the triplets comprising the triplet pair behave as independently as possible. We show that side chain sterics govern local packing in amorphous pentacene derivative nanoparticles, and that this in turn controls both the rate at which triplet pairs form and the rate at which they decay. We show how compact side chains and stronger couplings promote a triplet pair that effectively couples to the ground state, whereas bulkier side chains promote a triplet pair that appears more like two independent and long-lived triplet excitations. Our results show that the triplet pair is not emissive, that its decay is best viewed as internal conversion rather than triplet-triplet annihilation, and perhaps most critically that, in contrast to a number of recent suggestions, the triplets comprising the initially formed triplet pair cannot be considered independently. This work represents a significant step toward better understanding intermediates in singlet fission, and how molecular packing and couplings govern overall triplet yields.
We demonstrate a composite nanomaterial, termed an aptamer nano-flare, that can directly quantify an intracellular analyte in a living cell. Aptamer nano-flares consist of a gold nanoparticle core ...functionalized with a dense monolayer of nucleic acid aptamers with a high affinity for adenosine triphosphate (ATP). The probes bind selectively to target molecules and release fluorescent reporters which indicate the presence of the analyte. Additionally, these nanoconjugates are readily taken up by cells where their signal intensity can be used to quantify intracellular analyte concentration. These nanoconjugates are a promising approach for the intracellular quantification of other small molecules or proteins, or as agents that use aptamer binding to elicit a biological response in living systems.
Selenophene Electronics Hollinger, Jon; Gao, Dong; Seferos, Dwight S.
Israel journal of chemistry,
June 2014, Letnik:
54, Številka:
5-6
Journal Article
Recenzirano
Substituting individual heavier (or lighter) atoms would appear to be an extremely straightforward method of controlling the optoelectronic properties of π‐conjugated molecules that has minimal ...impact on solid‐state materials properties, yet things are never as they appear. Selenophenes are a distinct class of material separate from thiophenes. Their HOMOLUMO gap is often narrow, which is attractive for photonic applications. Intermolecular SeSe interactions increase ordering on a molecular scale and lead to distinct solid‐state organization, which often leads to excellent charge‐transport properties. The crystallization of selenophene is distinct from thiophenes, and thus, composites of selenophenes and other organic materials have distinct nano‐ and microscale morphologies. Some of the best organic optoelectronic devices use selenophene‐containing materials, yet early results were less encouraging. The most recent syntheses, structure determination, and electronic device properties of π‐conjugated selenophene‐based materials are reviewed. Significantly more work is justified and this review sets the stage for those studies.
Introduction of S-ethyl groups in all four ortho positions of azobenzene prevents reduction of the azo group by intracellular glutathione, while enhancing the absorptivity to ~10,000 M(-1) cm(-1) in ...the blue and green regions of the visible spectrum. cis-to-trans isomerization occurs thermally on the minutes timescale. Further, this substitution pattern permits switching with red light, a color that is more penetrating through biological tissues than other parts of the visible spectrum.
While controlled chain-growth polymerizations have been developed for a handful of p-type conjugated polymers, most n-type conjugated polymers are still synthesized through step-growth methods that ...offer little to no control over the polymerization. The anion-radical polymerization of thiophene-flanked naphthalene diimides has been shown to exhibit non-living chain-growth behavior; however, anion-radical polymerizations are limited to a few examples that exhibit varying degrees of control. Strategies to improve and expand the scope of this promising methodology have not been developed. In this study, we investigate the anion-radical polymerization of a series of oxygenated and thionated, thiophene- and selenophene-flanked naphthalene diimides. We show, through optical and spectroelectrochemical studies, that anion-radical monomers likely consist of a complex mixture of organic radicals with varying oxidation states. Surprisingly, subtle changes in monomer structure afforded by sulfur and selenium substitution result in significant changes in polymer synthesis. Notably, selenophene-flanked naphthalene diimides polymerize more rapidly to reach higher degrees of polymerization when compared to thiophene-flanked analogues. While thionated naphthalene diimides form anion-radical complexes and exhibit signs of catalyst insertion, they do not undergo polymerization. These results provide insights into the further development of anion-radical polymerization as a promising route to well-defined n-type conjugated polymers.
Organic electrodes are promising candidates for next-generation lithium-ion batteries due to their low cost and sustainable nature; however, they often suffer from very low conductivity and active ...material loadings. The conventional binder used in organic-based Li-ion batteries is poly(vinylidene fluoride) (PVDF), yet it is electrochemically inactive and thus occupies volume and mass without storing energy. Here, we report an organic mixed ionic-electronic conducting polymer, polynorbornene-1,2-bis(C(O)OPEDOT)25-b-norbornene-1,2-bis-(C(O)PEG12)25 denoted PEDOT-b-PEG for simplicity, as a cathode binder to address the aforementioned issues. The polymer contains a poly(3,4-ethylenedioxythiophene) (PEDOT) functionality to provide electronic conductivity, as well as poly(ethylene glycol) (PEG) chains to impart ionic conductivity to the cathode composite. We compare electrodes containing a perylene diimide (PDI) active material, conductive carbon, and a polymeric binder (either PVDF or PEDOT-b-PEG) with different weight ratios to study the impact of active material loading and type of binder on the performance of the cell. The lithium-ion cells prepared with the PEDOT-b-PEG polymer binder result in higher capacities and decreased impedance at all active material loadings compared to cathodes prepared with the PVDF-containing electrodes, demonstrating potential as a new binder to achieve higher active material loadings in organic electrodes. The strategy of preparing these polymers should be broadly applicable to other classes of mixed polymer conductors.
π‐Conjugated polymers have numerous applications due to their advantageous optoelectronic and mechanical properties. These properties depend intrinsically on polymer ordering, including ...crystallinity, orientation, morphology, domain size, and π–π interactions. Programming, or deliberately controlling the composition and ordering of π‐conjugated polymers by well‐defined inputs, is a key facet in the development of organic electronics. Here, π‐conjugated programming is described at each stage of material development, stressing the links between each programming mode. Covalent programming is performed during polymer synthesis such that complex architectures can be constructed, which direct polymer assembly by governing polymer orientation, π–π interactions, and morphological length‐scales. Solution programming is performed in a solvated state as polymers dissolve, aggregate, crystallize, or react in solution. Solid‐state programming occurs in the solid state and is governed by polymer crystallization, domain segregation, or gelation. Recent progress in programming across these stages is examined, highlighting order‐dependent features and assembly techniques that are unique to π‐conjugated polymers. This should serve as a guide for delineating the many ways of directing π‐conjugated polymer assembly to control ordering, structure, and function, enabling the further development of organic electronics.
π‐Conjugated polymer properties depend intrinsically on polymer order, including crystallinity, orientation, morphology, domain size, and π–π interactions. Order can be programmed through covalent bonding, i.e., molecular design, or through processing techniques in solution or solid‐state. This perspective serves as a guide to directing π‐conjugated polymer assembly, control polymer order, and thereby control its optical, electronic, and mechanical properties.
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