Epitaxially Intergrown Conformational Polymorphs and a Mixed Water/Methanol Solvate of 5′-Deoxy-5′-iodoguanosine

5′-Deoxy-5′-iodoguanosine (<b>I</b>) crystals deposited from mixtures of water and methanol grow as nonsolvated hybrids of conformational polymorphs (<b>Ia</b>, <b><b>Ib</b></b>) and as a mixed solvate (<b>Ic</b>). Some solvent-free crystals are purely <b>Ia</b>, while others have varying amounts of <b>Ib</b> epitaxially intergrown with <b>Ia</b>. In <b>Ia</b> and <b>Ib</b> the conformations differ primarily by torsion about the C4′–C5′ bond (guanosine numbering scheme), which dramatically affects the iodine atom position. Powder diffraction and reconstructed reciprocal-lattice-slice images had small peaks incompatible with <b>Ia</b>. Some solvent-free crystals required lattices for both <b>Ia</b> and <b>Ib</b> to index all observable reflections. Unit-cell dimensions for <b>Ia</b> and <b>Ib</b> suggest the potential for epitaxial intergrowth. Hydrogen-bond networks in <b>Ia</b> and <b>Ib</b> are essentially identical and result in double layers of molecules in the <i>ab</i> plane, with layers of iodine at the layer surfaces. The iodine layers of <b>Ia</b> and <b>Ib</b> are incompatible: in <b>Ia</b> adjacent iodine atom layers interdigitate slightly, whereas in <b>Ib</b> they do not. Theoretical calculations support the conclusion that at room temperature <b>Ia</b> is the thermodynamically more stable polymorph and that <b>Ib</b> represents a kinetic product

Epitaxially Intergrown Conformational Polymorphs and a Mixed Water/Methanol Solvate of 5′-Deoxy-5′-iodoguanosine

5′-Deoxy-5′-iodoguanosine (<b>I</b>) crystals deposited from mixtures of water and methanol grow as nonsolvated hybrids of conformational polymorphs (<b>Ia</b>, <b><b>Ib</b></b>) and as a mixed solvate (<b>Ic</b>). Some solvent-free crystals are purely <b>Ia</b>, while others have varying amounts of <b>Ib</b> epitaxially intergrown with <b>Ia</b>. In <b>Ia</b> and <b>Ib</b> the conformations differ primarily by torsion about the C4′–C5′ bond (guanosine numbering scheme), which dramatically affects the iodine atom position. Powder diffraction and reconstructed reciprocal-lattice-slice images had small peaks incompatible with <b>Ia</b>. Some solvent-free crystals required lattices for both <b>Ia</b> and <b>Ib</b> to index all observable reflections. Unit-cell dimensions for <b>Ia</b> and <b>Ib</b> suggest the potential for epitaxial intergrowth. Hydrogen-bond networks in <b>Ia</b> and <b>Ib</b> are essentially identical and result in double layers of molecules in the <i>ab</i> plane, with layers of iodine at the layer surfaces. The iodine layers of <b>Ia</b> and <b>Ib</b> are incompatible: in <b>Ia</b> adjacent iodine atom layers interdigitate slightly, whereas in <b>Ib</b> they do not. Theoretical calculations support the conclusion that at room temperature <b>Ia</b> is the thermodynamically more stable polymorph and that <b>Ib</b> represents a kinetic product

Tuning DNA Condensation with Zwitterionic Polyamidoamine (zPAMAM) Dendrimers

Cationic dendrimers are promising vectors for nonviral gene therapies due to their well-defined size and chemistry. We have synthesized a series of succinylated fourth generation (G4) PAMAM dendrimers to control the DNA packaging in dendriplexes, allowing us to probe the role of charge on DNA packaging. The self-assembly of DNA induced by these zwitterionic PAMAM (zPAMAM) was investigated using small-angle X-ray scattering (SAXS). We demonstrate that changing the degree of modification in zPAMAM–DNA significantly alters the packing density of the resulting dendriplexes. Salt sensitivities and pH dependence on the inter-DNA spacing were also examined. The swelling and stability to salt are reduced with increasing degree of PAMAM modification. Lowering the pH leads to significantly tighter hexagonal DNA packaging. In combination, these results show zPAMAM is an effective means to modulate nucleic acid packaging in a deterministic manner

Controlling Oxidation Potentials in Redox Shuttle Candidates for Lithium-Ion Batteries

Overcharge, a condition in which cell voltage rises to undesirably high potentials, can be prevented in lithium-ion batteries by incorporating redox shuttles into the battery electrolyte. Although extensive overcharge protection has been demonstrated in batteries with LiFePO₄ cathodes, the redox shuttles that work in these batteries are incompatible with higher voltage cathodes. Designing stable additives with higher oxidation potentials is necessary to protect high voltage batteries from overcharge. Toward that goal, we synthesized diarylamines with varied structures, including fused heteroaromatic ring systems and electron-withdrawing substituents. We found that trends in oxidation potentials correlated with those in calculated adiabatic ionization potentials. Some diarylamine derivatives protected batteries from overcharge with varying degrees of success

Synthesis and Electrical Properties of Derivatives of 1,4-bis(trialkylsilylethynyl)benzo[2,3‑<i>b</i>:5,6‑<i>b</i>′]diindolizines

A new class of nitrogen-containing arene organic semiconductors incorporating fused indolizine units is described. This system, though having a zigzag shape, mimics the electronic properties of its linear analogue pentacene as a result of nitrogen lone pair incorporation into the π-electron system. Solubilizing trialkylsilylethynyl groups were employed to target crystal packing motifs appropriate for field-effect transistor devices. The triethylsilylethynyl derivative yielded hole mobilities of 0.1 cm² V^–1 s^–1 and on/off current ratios of 10⁵

Structural Isomerization of 2‑Anilinonicotinic Acid Leads to a New Synthon in 6‑Anilinonicotinic Acids

Through structural modification of 2-anilinonicotinic acid by isomerization, a new synthon, acid-aminopyridine, is created, and the two original synthons, i.e., the acid–acid homosynthon and acid–pyridine heterosynthon are no longer observed in the newly designed 6-anilinonicotinic acids. The new synthon has a hydrogen-bond strength rivaling that of the acid–acid homosynthon and the acid–pyridine heterosynthon, as suggested by theoretical calculations, which explains its formation

Effect of Halogenation on the Energetics of Pure and Mixed Phases in Model Organic Semiconductors Composed of Anthradithiophene Derivatives and C₆₀

Halogenation, particularly fluorination, is commonly used to manipulate the energetics, stability, and morphology of organic semiconductors. In the case of organic photovoltaics (OPVs), fluorination of electron donor molecules or polymers at appropriate positions can lead to improved performance. In this contribution, we use ultraviolet photoelectron spectroscopy, external quantum efficiency measurements of charge-transfer (CT) states, and density functional theory calculations to systematically investigate the effects of halogenation on the bulk solid-state energetics of model anthradithiophene (ADT) materials, their interfacial energetics with C₆₀, and the energetics of various ADT:C₆₀ blend compositions. In agreement with previous work, nonhalogenated ADT molecules show higher energy CT states in blends with C₆₀ and lower energy CT states in the ADT/C₆₀ bilayers. However, this trend is reversed in the halogenated ADT/C₆₀ systems, wherein the CT state energies of ADT:C₆₀ blends are lower than those in the bilayers. In bulk-heterojunction photovoltaics, the lower energy CT states present in the mixed phase with the halogenated ADT derivatives will likely decrease the probability of charge separation and increase charge recombination. The less favorable energy landscapes observed upon halogenation suggest that the benefits of fluorination observed in many OPV material systems may be more due to morphological factors

Processing Dependent Influence of the Hole Transport Layer Ionization Energy on Methylammonium Lead Iodide Perovskite Photovoltaics

Organometal halide perovskite photovoltaics typically contain both electron and hole transport layers, both of which influence charge extraction and recombination. The ionization energy (IE) of the hole transport layer (HTL) is one important material property that will influence the open-circuit voltage, fill factor, and short-circuit current. Herein, we introduce a new series of triarylamino­ethynylsilanes with adjustable IEs as efficient HTL materials for methyl­ammonium lead iodide (MAPbI₃) perovskite based photovoltaics. The three triarylamino­ethynylsilanes investigated can all be used as HTLs to yield PV performance on par with the commonly used HTLs PEDOT:PSS and Spiro-OMeTAD in inverted architectures (i.e., HTL deposited prior to the perovskite layer). We further investigate the influence of the HTL IE on the photovoltaic performance of MAPbI₃ based inverted devices using two different MAPbI₃ processing methods with a series of 11 different HTL materials, with IEs ranging from 4.74 to 5.84 eV. The requirements for the HTL IE change based on whether MAPbI₃ is formed from lead acetate, Pb­(OAc)₂, or PbI₂ as the Pb source. The ideal HTL IE range is between 4.8 and 5.3 eV for MAPbI₃ processed from Pb­(OAc)₂, while with PbI₂ the PV performance is relatively insensitive to variations in the HTL IE between 4.8 and 5.8 eV. Our results suggest that contradictory findings in the literature on the effect of the HTL IE in perovskite photovoltaics stem partly from the different processing methods employed

Processing Dependent Influence of the Hole Transport Layer Ionization Energy on Methylammonium Lead Iodide Perovskite Photovoltaics

Organometal halide perovskite photovoltaics typically contain both electron and hole transport layers, both of which influence charge extraction and recombination. The ionization energy (IE) of the hole transport layer (HTL) is one important material property that will influence the open-circuit voltage, fill factor, and short-circuit current. Herein, we introduce a new series of triarylamino­ethynylsilanes with adjustable IEs as efficient HTL materials for methyl­ammonium lead iodide (MAPbI₃) perovskite based photovoltaics. The three triarylamino­ethynylsilanes investigated can all be used as HTLs to yield PV performance on par with the commonly used HTLs PEDOT:PSS and Spiro-OMeTAD in inverted architectures (i.e., HTL deposited prior to the perovskite layer). We further investigate the influence of the HTL IE on the photovoltaic performance of MAPbI₃ based inverted devices using two different MAPbI₃ processing methods with a series of 11 different HTL materials, with IEs ranging from 4.74 to 5.84 eV. The requirements for the HTL IE change based on whether MAPbI₃ is formed from lead acetate, Pb­(OAc)₂, or PbI₂ as the Pb source. The ideal HTL IE range is between 4.8 and 5.3 eV for MAPbI₃ processed from Pb­(OAc)₂, while with PbI₂ the PV performance is relatively insensitive to variations in the HTL IE between 4.8 and 5.8 eV. Our results suggest that contradictory findings in the literature on the effect of the HTL IE in perovskite photovoltaics stem partly from the different processing methods employed

Processing Dependent Influence of the Hole Transport Layer Ionization Energy on Methylammonium Lead Iodide Perovskite Photovoltaics

Organometal halide perovskite photovoltaics typically contain both electron and hole transport layers, both of which influence charge extraction and recombination. The ionization energy (IE) of the hole transport layer (HTL) is one important material property that will influence the open-circuit voltage, fill factor, and short-circuit current. Herein, we introduce a new series of triarylamino­ethynylsilanes with adjustable IEs as efficient HTL materials for methyl­ammonium lead iodide (MAPbI₃) perovskite based photovoltaics. The three triarylamino­ethynylsilanes investigated can all be used as HTLs to yield PV performance on par with the commonly used HTLs PEDOT:PSS and Spiro-OMeTAD in inverted architectures (i.e., HTL deposited prior to the perovskite layer). We further investigate the influence of the HTL IE on the photovoltaic performance of MAPbI₃ based inverted devices using two different MAPbI₃ processing methods with a series of 11 different HTL materials, with IEs ranging from 4.74 to 5.84 eV. The requirements for the HTL IE change based on whether MAPbI₃ is formed from lead acetate, Pb­(OAc)₂, or PbI₂ as the Pb source. The ideal HTL IE range is between 4.8 and 5.3 eV for MAPbI₃ processed from Pb­(OAc)₂, while with PbI₂ the PV performance is relatively insensitive to variations in the HTL IE between 4.8 and 5.8 eV. Our results suggest that contradictory findings in the literature on the effect of the HTL IE in perovskite photovoltaics stem partly from the different processing methods employed