Conjugated polymers may play an important role in various emerging optoelectronic applications because they combine the chemical versatility of organic molecules and the flexibility, stretchability and toughness of polymers with semiconducting properties. Nevertheless, in order to achieve the full potential of conjugated polymers, a clear description of how their structure, morphology, and macroscopic properties are interrelated is needed. We propose that the starting point for understanding conjugated polymers includes understanding chain conformations and phase behavior. Efforts to predict and measure the persistence length have significantly refined our intuition of the chain stiffness, and have led to predictions of nematic-to-isotropic transitions. Exploring mixing between conjugated polymers and small molecules or other polymers has demonstrated tremendous advancements in attaining the needed properties for various optoelectronic devices. Current efforts continue to refine our knowledge of chain conformations and phase behavior and the factors that influence these properties, thereby providing opportunities for the development of novel optoelectronic materials based on conjugated polymers.

While ∼75% of commercially utilized polymers are semicrystalline, the generally low mechanical modulus of these materials, especially for those possessing a glass transition temperature below room temperature, restricts their use for structural applications. Our focus in this paper is to address this deficiency through the controlled, multiscale assembly of nanoparticles (NPs), in particular by leveraging the kinetics of polymer crystallization. This process yields a multiscale NP structure that is templated by the lamellar semicrystalline polymer morphology and spans NPs engulfed by the growing crystals, NPs ordered into layers in the interlamellar zone [spacing of (10–100 nm)], and NPs assembled into fractal objects at the interfibrillar scale, (1–10 μm). The relative fraction of NPs in this hierarchy is readily manipulated by the crystallization speed. Adding NPs usually increases the Young’s modulus of the polymer, but the effects of multiscale ordering are nearly an order of magnitude larger than those for a state where the NPs are not ordered, i.e., randomly dispersed in the matrix. Since the material’s fracture toughness remains practically unaffected in this process, this assembly strategy allows us to create high modulus materials that retain the attractive high toughness and low density of polymers.

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Relative to the rich library of small-molecule organics, few examples of ordered extended (i.e., nonmolecular) hydrocarbon networks are known. In particular, sp 3 bonded, diamond-like materials represent appealing targets because of their desirable mechanical, thermal, and optical properties. While many covalent organic frameworks (COFs)extended, covalently bonded, and porous structureshave been realized through molecular architecture with exceptional control, the design and synthesis of dense, covalent extended solids has been a longstanding challenge. Here we report the preparation of a sp 3 -bonded, low-dimensional hydrocarbon synthesized via high-pressure, solid-state diradical polymerization of cubane (C 8 H 8 ), which is a saturated, but immensely strained, cage-like molecule. Experimental measurements show that the obtained product is crystalline with three-dimensional order that appears to largely preserve the basic structural topology of the cubane molecular precursor and exhibits high hardness (comparable to fused quartz) and thermal stability up to 300 °C. Among the plausible theoretical candidate structures, one-dimensional carbon scaffolds comprising six-and four-membered rings that pack within a pseudosquare lattice provide the best agreement with experimental data. These diamond-like molecular rods with extraordinarily small thickness are among the smallest members in the carbon nanothread family, and calculations indicate one of the stiffest one-dimensional systems known. These results present opportunities for the synthesis of purely sp 3 -bonded extended solids formed through the strain release of saturated molecules, as opposed to only unsaturated precursors.

Junction-functionalized donor-acceptor (D-A) block copolymers (BCPs) enable spatial and electronic control over interfacial charge dynamics in excitonic devices such as solar cells. Here we present the design, synthesis, morphology and electronic characterization of block junctionfunctionalized, all-conjugated, all-crystalline D-A BCPs. Poly(3-hexylthiophene) (P3HT), a single thienylated diketopyrrolopyrrole (Th x DPPTh x , x=1 or 2) unit and poly{[N,N'-bis(2octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (PNDIT2) is used as donor, interfacial unit and acceptor, respectively. Almost all C-C coupling steps are accomplished by virtue of C-H activation. Synthesis of the macroreagent H-P3HT-Th x DPPTh x , with x determining its C-H reactivity, is key to the synthesis of various BCPs of type H-P3HT-Th x DPPTh x -block-PNDIT2. Remarkable morphological behavior is determined from a combination of calorimetry, transmission electron microscopy (TEM) and thin film scattering. Block copolymer crystallinity of P3HT and PNDIT2 is reduced indicating frustrated crystallization. A long period l p , is invisible from TEM, but shows up in resonant soft X-ray scattering experiments on a length scale of l p ~60 nm. Charge transfer photoluminescence of H-P3HT-Th x DPPTh x indicates efficient transfer of the excitation energy to the DPP chain end, but is quenched in BCP films. Transient absorption and pump-push-photocurrent spectroscopies reveal geminate recombination (GR) as the main loss channel in as-prepared BCP films independent of junction functionalization. Melt-annealing increases GR as a result of the low degree of crystallinity and poorly defined interfaces, and additionally changes backbone orientation of PNDIT2 from face-on to edge-on. These morphological effects dominate solar cell performance and cause an insensitivity to the presence of the block junction.

Microphase-separated block copolymers composed of electron donor and acceptor blocks may provide morphology control to address many challenges in organic electronics. Crucial to controlling the self-assembly of fully conjugated block copolymers is tuning the interplay between crystallization of the individual blocks and microphase separation between the donor and the acceptor. Thus, we have examined the kinetics of the morphological evolution in P3HT-b-PFTBT block copolymer films during two processes: solution casting and thermal annealing. We use in situ wide-angle and small-angle grazing incidence X-ray scattering to monitor the crystallization of P3HT and microphase separation between the two blocks. We find that during film drying, initial P3HT crystallization happens quickly, before phase separation of the two blocks. However, crystallization is significantly suppressed with respect to neat materials, enabling microphase separation to proceed at time scales after some initial crystallization of the donor block takes place. This enables a mesoscale structure to develop during processes such as thermal annealing because self-assembly of the lamellar structure takes place before the crystallization of the donor block is complete. We also find that significant crystallization of PFTBT blocks after P3HT crystallization is possible at elevated temperatures. Crystallization of both blocks is important to maximize the performance of solar cells and transistors with block copolymer active layers. As a consequence, we exceed 3% average power conversion efficiencies in P3HT-b-PFTBT photovoltaic devices.

Fully conjugated donor–acceptor block copolymers are established as model systems to elucidate fundamental mechanisms of photocurrent generation in organic photovoltaics. Using analysis of steady‐state photoluminescence quenching, exciton dissociation to a charge transfer state within individual block copolymer chains is quantified. By making a small adjustment to the conjugated backbone, the electronic properties are altered enough to disrupt charge transfer almost entirely. Strong intermolecular coupling of the electron donor is introduced by synthesizing block copolymer nanoparticles. Transient absorption spectroscopy is used to monitor charge generation in block copolymer isolated chains and nanoparticles. While efficient charge transfer is observed in isolated chains, there is no indication of complete charge separation. In the nanoparticles, long‐lived polarons are observed as early as ≈15 ns. Thus, aggregation of electron donors can facilitate efficient charge generation.

Aqueous alkali -ion batteries offer an economical method for large-scale energy storage demanded by current sources of renewable energy. Although NASICON-type NaTi 2 (PO 4 ) 3 is an attractive anode material with high capacity and a low redox potential allowing for high voltage cells, it suffers from considerable capacity fade when cycled slowly and deeply. In this work polypyrrole has been introduced as a coating for NaTi 2 (PO 4 ) 3 through a high-energy ballmilling process. When an excessive coating was applied, no redox reactions from the NaTi 2 (PO 4 ) 3 were visible due to the poor Na + diffusion through the polypyrrole. However, the as-coated composites containing 5 wt% polypyrrole showed much better capacity retention compared to the uncoated material, retaining 57% of the initial discharge capacity after 50 cycles compared to the uncoated material, which retained only 10% of the initial discharge capacity. It is concluded that coating NaTi 2 (PO 4 ) 3 with conducting polymers can be an effective strategy for promoting battery lifetime. Large-scale energy storage is needed for the deployment of gridtied and distributed renewable energy sources such as solar installations and wind farms, which rely on power generation that is inherently intermittent. For this kind of storage, the single most important performance attribute is the amortized cost of stored electricity over the life of the energy storage device; as such long life and robustness through thousands of use cycles are critical attributes.1,2 As such, we have sought to develop low cost, easy to manufacture battery chemistries that are composed of benign materials and have the necessary long-term stability. Neutral pH aqueous based battery systems are well suited for this purpose. The higher conductivity of aqueous electrolytes allows for thicker electrodes, low cost electrolyte salts such as Li 2 SO 4 and Na 2 SO 4 can be used in place of LiPF 6 , and nonwoven cellulose separators can be used in place of more expensive porous polyolefins. ,9-11,15,19-27 as anode materials. While a significant amount of research has been carried out on the failure mechanism of cathode materials, little has been done to elucidate the anode material role in battery failure in aqueous electrolytes. Furthermore, there are some cathode systems that have exhibited many thousands of stable cycles without loss in function, 8,28 while materials at useful anode potentials tend to lose function rapidly. 23,29 Of particular interest are the sodium super ionic conductor (NA-SICON) titanium phosphates due to their high ionic conductivities, relative low cost of production, and chemical stability. 11,24,25 In particular, NaTi 2 (PO 4 ) 3 with a theoretical capacity of 133 mAh/g and the ability to replace lithium salts with sodium equivalents should offer a cost-effective alternative to the lithium equivalent. However, this material commonly exhibits significant capacity fade, especially when cycled deeply/slowly, and the phenomena responsible for this loss in function remains p...