Density functional theory (DFT) calculations are useful to model orbital energies of conjugated polymers, yet discrepancy between theory and experiment exist. Here we evaluate a series of relatively straightforward calculation methods using the standard Gaussian 09 software package. Five calculations were performed on 22 different conjugated polymer model compounds at the B3LYP and CAM-B3LYP levels of theory and results compared with experiment. Chain length saturation occurs at approximately 6 and 4 repeat units for homo- and donor–acceptor type conjugated polymers, respectively. The frontier orbital energies are better approximated using B3LYP than CAM-B3LYP, and the HOMO energy can be reasonably correlated with experiment [mean signed error (MSE) = 0.22 eV]. The LUMO energies, however are poorly correlated (MSE = 0.59 eV), and we show that the molecular orbital energy of the triplet state gives a much better estimate of the experimentally determined LUMO level (MSE = −0.13 eV).

Electron-deficient π-conjugated polymers are important for organic electronics, yet the ability to polymerize electron-deficient monomers in a controlled manner is challenging. Here we show that Ni(II)diimine catalysts are well suited for the controlled polymerization of electron-deficient heterocycles. The relative stability of the calculated catalyst-monomer (or catalyst-chain end) complex directly influences the polymerization. When the complex is predicted to be most stable (139.2 kJ/mol), these catalysts display rapid reaction kinetics, leading to relatively low polydispersities (∼1.5), chain lengths that are controlled by monomer:catalyst ratio, controlled monomer consumption up to 60% conversion, linear chain length growth up to 40% conversion, and 'living' chain ends that can be readily extended by adding more monomer. These are desirable features that highlight the importance of catalyst design for the synthesis of new conjugated polymers.

We use a Ni(II) diimine catalyst to prepare the first examples of the controlled synthesis of electron-rich/ electron-deficient all-conjugated diblock copolymers. These catalysts are able to control polymerizations of both electronrich and electron-deficient monomers, which we attribute to strong association to both monomer types. Block copolymers are prepared by controlled chain extension, and their structure is verified by gel permeation chromatography, 1 H NMR, electrochemistry, calorimetry, and atomic force microscopy.

The role of ion placement was systematically investigated in imidazolium bis­(trifluoromethane)­sulfonimide (ImTFSI) polymerized ionic liquids (PILs) containing pendant charges and charges in the backbone (sometimes called ionenes). The backbone PILs were synthesized via a facile step growth route, and pendant PILs were synthesized via RAFT. Both PILs were designed to have nearly identical charge density, and the conductivity was found to be substantially enhanced in the backbone PIL systems even after accounting for differences in the glass transition temperature (T g). Wide-angle X-ray scattering (WAXS) revealed an invariance in the location of the amorphous halo between the two systems, while the anion–anion correlation peak was shifted to lower scattering wavevector (q) in the backbone PILs. This indicates an increase in the correlation length of ions and is consistent with charge transport along a more correlated pathway following the polymer backbone. Due to the linear nature of the backbone PILs, crystallization was observed and correlated with changes in conductivity. Upon crystallization, the conductivity dropped, and eventually, two populations of mobile ions were observed and attributed to ions in the amorphous and near-crystallite regions. The present work demonstrates the important role of ion placement on local structure and conductivity as well as the ability of backbone PILs to be used as controllable optical or dielectric materials based on crystallization or processing history.

Controlling crystallinity and molecular packing at nano- and macroscopic length scales in conjugated polymer thin films is vital for improving the performance of polymer-based electronic devices. Herein, the inherent amphiphilicity of rigid donor–acceptor copolymers used in high performance polymer electronics is leveraged to allow the formation of highly ordered lyotropic mesophases. By increasing the length and branching of solubilizing chains on cyclopenta­dithiophene-alt-thiadiazolo­pyridine-based alternating copolymers, amphiphilicity can be increased, and lyotropic liquid crystalline mesophases are observed in selective solvents. These lyotropic mesophases consist of chain extended polymers exhibiting close, ordered π-stacking. This is evidenced by birefringent solutions and red-shifted absorbance spectra displaying pronounced excitonic coupling. Crystallinity developed in solution can be transferred to the solid state, and thin films of donor–acceptor copolymers cast from lyotropic solutions exhibit improved crystalline order in both the alkyl and π-stacking directions. Because of this improved crystallinity, transistors with active layers cast from lyotropic solutions exhibit a significant improvement in carrier mobility compared to those cast from isotropic solution, reaching a maximum value of 0.61 cm2 V–1 s–1. This approach of rational side chain design bridges the gap from solution structure to solid state structure and is a promising and general approach to allow the expression of lyotropic mesophases in rigid conjugated polymers.

Biologically derived organic molecules are a cost‐effective and environmentally benign alternative to the widely used metal‐based electrodes employed in current energy storage technologies. Here, the first bio‐derived pendant polymer cathode for lithium‐ion batteries is reported. The redox moiety is flavin and is derived from riboflavin (vitamin B2). A semi‐synthetic methodology is used to prepare the pendant polymer, which is composed of a poly(norbornene) backbone and pendant flavin units. This semi‐synthetic approach reduces the number of chemical transformations required to form this new functional material. Lithium‐ion batteries incorporating this polymer have a 125 mAh g−1 capacity and an ≈2.5 V operating potential. It is found that charge transport is greatly improved by forming hierarchical structures of the polymer with carbon black, and new insight into electrode degradation mechanisms is provided which should be applicable to polymer electrodes in general. This work provides a foundation for the use of bio‐derived pendant polymers in sustainable, high‐performance lithium‐ion batteries.

Intermolecular interactions in conjugated polymers influence crystallinity, self-assembly, and packing motif, factors which in turn crucially impact charge transport properties such as carrier mobility in organic electronic devices. Correlated alignment of molecular and crystalline morphologies provides direct pathways for charge carriers to follow; however, the role of intermolecular interactions in achieving this is unexplored. Herein, we synthesize a series of lyotropic liquid crystalline conjugated polymers with variable side-chain structure to lend distinct steric repulsion and van der Waals attractive forces to each mesophase. We use this to investigate the role of intermolecular interactions on mesophase alignment. The strength of intermolecular interaction for each mesophase is compared by measuring melting temperature, π-stacking distance, and the Maier−Saupe interaction parameter. In general we find that side-chain structure can impact interaction strength by varying steric repulsion and backbone attractions and that the Maier−Saupe interaction parameters correlate with higher degrees of alignment after shearing, achieving a dichroic absorbance ratio of up to 2. This observation is used to develop equilibrium processing methods for fabricating macroscopically aligned polymer substrates used in transistors, improving mobility by a factor of 3 compared to spin-coated devices.

The optoelectronic properties of conjugated polymers are dictated by their chain conformations, which depend on the interplay of delocalization of electrons along the π-conjugated backbone and the intrachain interactions of pendant side chains. Here, we leverage small-angle neutron scattering to measure the chain shapes of several classes of commonly used, high mobility donor–acceptor conjugated polymers in dilute solution. We find that these model conjugated polymers are semiflexible with persistence lengths ranging from several to hundreds of nanometers, dependent on the molecular structure of the polymer, indicating the importance of repeat unit geometry, particularly side-chain size and branching, on the overall chain conformations. The measured persistence lengths show good agreement with those calculated according to dihedral distributions predicted from density functional theory. Larger persistence lengths are shown to correlate with increased charge-carrier mobility, signifying the importance of rational molecular design to obtain high persistence length organic semiconductors and thus advantageous optoelectronic properties.