Conjugated polymers with a donor–acceptor (DA) structural motif have found extensive use in a wide variety of optoelectronic devices; however, despite their ubiquity in the literature, the vast majority of these materials are simple alternating copolymersone electron donor alternates with one electron acceptor in the polymer backbone. As a result, the impact of composition (e.g., donor/acceptor ratio) and structure (e.g., alternating, block, or random) on the optoelectronic properties of these copolymers remains poorly understood. In this work, the number of acceptor units in alternating DA copolymers is systematically increased. Two dimers of the common electron acceptor isoindigo are synthesized, one with free rotation between the subunits and one with enforced coplanarity. The two dimers are then used to synthesize donor–acceptor–acceptor (DAA) copolymers with either thiophene or terthiophene comonomers. These DAA polymers feature two electron acceptors in their repeat unit, and their optoelectronic properties are compared to those of the analogous DA polymers. It is shown that increasing the number of acceptor units causes a decrease in the LUMO energy of the resulting polymer; this effect is enhanced by enforcing coplanarity between acceptor units via ring fusion. All six polymers were tested in both organic photovoltaics (OPVs) and organic thin film transistors (OTFTs). While the DA polymers performed better in OPVs, the DAA polymers displayed more balanced charge carrier mobilities in OTFTs.

Understanding the effect of surface chemistry on the dielectric−semiconductor interface, thin-film morphology, and molecular alignment enables the optimization of organic thin-film transistors (OTFTs). We explored the properties of thin films of bis(pentafluorophenoxy) silicon phthalocyanine (F 10 -SiPc) evaporated onto silicon dioxide (SiO 2 ) surfaces modified by self-assembled monolayers (SAMs) of varying surface energies and by weak epitaxy growth (WEG). The total surface energy (γ tot ), dispersive component of the total surface energy (γ d ), and polar component of the total surface energy (γ p ) were calculated using the Owens−Wendt method and related to electron field-effect mobility of devices (μ e ), and it was determined that minimizing γ p and matching γ tot yielded films with the largest relative domain sizes and highest resulting μ e . Subsequent analyses were completed using atomic force microscopy (AFM) and grazing-incidence wide-angle X-ray scattering (GIWAXS) to relate surface chemistry to thin-film morphology and molecular order at the surface and semiconductor−dielectric interface, respectively. Films evaporated on n-octyltrichlorosilane (OTS) yielded devices with the highest average μ e of 7.2 × 10 −2 cm 2 •V −1 •s −1 that we attributed to it having both the largest domain length, which were extracted from power spectral density function (PSDF) analysis, and a subset of molecules with a pseudo edge-on orientation relative to the substrate. Films of F 10 -SiPc with the mean molecular orientation of the π-stacking direction being more edge-on relative to the substrate also generally resulted in OTFTs with a lower average V T . Unlike conventional MPcs, F 10 -SiPc films fabricated by WEG experienced no macrocycle in an edge-on configuration. These results demonstrate the critical role of the F 10 -SiPc axial groups on WEG, molecular orientation, and film morphology as a function of surface chemistry and the choice of SAMs.

The synthesis of two neutral acridone derivatives was carried out to design media sensitive chromophores by taking advantage of intramolecular charge transfer (ICT) features. The molecules comprised two different donor-acceptor-donor triads, with absorption maxima at 425 nm and 520 nm, for the ketone and dicyanomethylene derivatives, respectively. The ketone variant exhibited fluorescence at room temperature, whereas the dicyanomethylene derivative was only emissive in frozen hexane. The ketone emission was highly solvatochromic, with Stokes shifts that ranged from 5000 cm(-1) to 10 000 cm(-1). Electrochemically, both compounds displayed similar oxidation potentials at approximately 0.35 V versus ferrocene/ferrocenium, which was anticipated since both systems employ the same ethynylaniline donor portion of the molecule, whereas only the 9-dicyanomethylene derivative showed a reduction peak at -1.5 V vs. Fc/Fc(+). Additional spectroelectro-chemical experiments supported a delocalized cationic charge on the ethynylaniline fragments during oxidation and that during electrochemical reduction the dicyanomethylene moieties show localized anionic charge. All of the experimental observations are finally compared to DFT, TDDFT and NICS(0) computations to gain insight into the transitions involved and deduce the role of the acridone core in stabilizing its oxidized and reduced forms.

Anion-exchange membrane water electrolysis (AEMWE) is a promising technology for low-cost, high-efficiency, green hydrogen production. The stability of the AEM is a critical issue but difficult to delineate in situ from degradation of the catalyst layer (CL). Moreover, the porous transport layer (PTL) can contribute electrocatalytically. Herein, we demonstrate that stainless steel (SS) felt, in the absence of an anode CL, is highly active toward the oxygen evolution reaction (OER) (1 A cm −2 at 1.74 V cell ) and serves as a combined OER electrocatalyst and PTL, thus simplifying the study of AEMs in water electrolyzers. We further show that Ni felt exhibits much lower OER activity than SS felt, which suggests that in situ studies of OER electrocatalysts and CL compositions should be performed with Ni felt, not SS felt, to reduce OER contributions from the PTL. Lastly, we found that the substrate for depositing the cathode CL, AEM, or PTL strongly influences the rate of H 2 crossover.