Revealing the Singlet Fission Mechanism for a Silane-Bridged Thienotetracene Dimer

Tetraceno[2,3-b]thiophene is regarded as a strong candidate for singlet fission-based solar cell applications due to its mixed characteristics of tetracene and pentacene that balance exothermicity and triplet energy. An electronically weakly coupled tetraceno[2,3-b]thiophene dimer (Et2Si(TIPSTT)2) with a single silicon atom bridge has been synthesized, providing a new platform to investigate the singlet fission mechanism involving the two acene chromophores. We study the excited state dynamics of Et2Si(TIPSTT)2 by monitoring the evolution of multiexciton coupled triplet states, 1TT to 5TT to 3TT to T1 + S0, upon photoexcitation with transient absorption, temperature-dependent transient absorption, and transient/pulsed electron paramagnetic resonance spectroscopies. We find that the photoexcited singlet lifetime is 107 ps, with 90% evolving to form the TT state, and the complicated evolution between the multiexciton states is unraveled, which can be an important reference for future efforts toward tetraceno[2,3-b]thiophene-based singlet fission solar cells.

Crystal structures of two formamidinium hexa-fluorido-phosphate salts, one with batch-dependent disorder

Syntheses of the acyclic amidinium salts, morpholino-formamidinium hexa-fluorido-phosphate [OC4H8N-CH=NH2]PF6 or C5H11N2O+·PF6 -, 1, and pyrrolidinoformamidinium hexa-fluorido-phosphate [C4H8N-CH= NH2]PF6 or C5H11N2 +·PF6 -, 2, were carried out by heating either morpholine or pyrrolidine with triethyl orthoformate and ammonium hexa-fluorido-phosphate. Crystals of 1 obtained directly from the reaction mixture contain one cation and one anion in the asymmetric unit. The structure involves cations linked in chains parallel to the b axis by N-H⋯O hydrogen bonds in space group Pbca, with glide-related chains pointing in opposite directions. Crystals of 1 obtained by recrystallization from ethanol, however, showed a similar unit cell and the same basic structure, but unexpectedly, there was positional disorder [occupancy ratio 0.639 (4):0.361 (4)] in one of the cation chains, which lowered the crystal symmetry to the non-centrosymmetric space group Pca21, with two cations and anions in the asymmetric unit. In the pyrrolidino compound, 2, cations and anions are ordered and are stacked separately, with zigzag N-H⋯F hydrogen-bonding between stacks, forming ribbons parallel to (101), extended along the b-axis direction. Slight differences in the delocalized C=N distances between the two cations may reflect the inductive effect of the oxygen atom in the morpholino compound.

Hydrogen-Bonding Trends in a Bithiophene with 3- and/or 4-Pyridyl Substituents

To improve the charge-carrier transport capabilities of thin-film organic materials, the intermolecular electronic couplings in the material should be maximized. Decreasing intermolecular distance while maintaining proper orbital overlap in highly conjugated aromatic molecules has so far been a successful way to increase electronic coupling. We attempted to decrease the intermolecular distance in this study by synthesizing cocrystals of simple benzoic acid coformers and dipyridyl-2,2'-bithiophene molecules to understand how the coformer identity and pyridine N atom placement affected solid-state properties. We found that with the 5-(3-pyridyl)-5'-(4-pyridyl)-isomer, the 4-pyridyl ring interacted with electrophiles and protons more strongly. Synthesized cocrystal powders were found to have reduced average crystallite size in reference to the parent compounds. The opposite was found for the intermolecular electronic couplings, as determined via density functional theory (DFT) calculations, which were relatively large in some of the cocrystals.

Syntheses and crystal structures of 4-(4-methoxyphenyl)piperazin-1-ium 4-methylbenzoate monohydrate and bis[4-(4-methoxyphenyl)piperazin-1-ium] benzene-1,2-dicarboxylate

Co-crystallization of N-(4-methoxyphenyl)piperazine with 4-methylbenzoic acid and with benzene-1,2-dicarboxylic acid yields the salts 4-(4-methoxyphenyl)piperazin-1-ium 4-methylbenzoate monohydrate, C11H17N2O+·C8H7O2 −·H2O (I), and bis[4-(4-methoxyphenyl)piperazin-1-ium] benzene-1,2-dicarboxylate, 2C11H17N2O+·C8H4O4 2− (II). These salts both crystallize with Z′ = 2, in space groups P\overline{1} and Pna21, respectively. In compound (I), a combination of four O—H...O, four N—H...O, one C—H...O and one C—H...π(arene) hydrogen bonds link the six independent components into complex sheets, within which the two piperazine rings, the two anions, and the two water molecules are related by an approximate, non-crystallographic translation along the b-axis direction. In compound (II), sheets containing R 4 4(18) and R 10 12(38) rings are formed by the combined action of eight independent N—H...O hydrogen bonds. Comparisons are made with the structures of some related compounds.

Syntheses and crystal structures of 4-(4-nitrophenyl)piperazin-1-ium benzoate monohydrate and 4-(4-nitrophenyl)piperazin-1-ium 2-carboxy-4,6-dinitrophenolate

Two new salts of the 4-(4-nitro­phen­yl)piperazin-1-ium cation have been prepared by co-crystallization with aromatic carb­oxy­lic acids. The supra­molecular assembly in the benzoate salt, which crystallizes as a mono-hydrate, is two dimensional, while that in the 2-carb­oxy-4,6-di­nitro­phenolate salt is three dimensional.

Crystal structures are reported for two mol­ecular salts containing the 4-(4-nitro­phen­yl)piperazin-1-ium cation. Co-crystallization from methanol/ethyl acetate solution of N-(4-nitro­phen­yl)piperazine with benzoic acid gives the benzoate salt, which crystallizes as a monohydrate, C₁₀H₁₄N₃O₂·C₇H₅O₂·H₂O, (I), and similar co-crystallization with 3,5-di­nitro­salicylic acid yields the 2-carb­oxy-4,6-di­nitro­phenolate salt, C₁₀H₁₄N₃O₂·C₇H₃N₂O₇, (II). In the structure of (I), a combination of O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds links the components into sheets, while in the structure of (II), the supra­molecular assembly, generated by hydrogen bonds of the same types as in (I), is three dimensional. Comparisons are made with the structures of some related compounds.

π-π Stacking in the Polymorphism of 2-(Naphthalenylamino)-nicotinic Acids and A Comparison with Their Analogues

Substituent size and isomerization played an important role in the polymorphism of 2-(naphthalen-n-ylamino)-benzoic acids (n = 1, 2; 2-NBAs) as each of the two previously investigated 2-NBAs was found to...

Conformational Flexibility and Substitution Pattern Lead to Polymorphism of 3-Methyl-2-(phenylamino)benzoic acid

To probe the effect of substitution on the benzoic acid ring on the polymorphism of phenylaminobenzoic acids, five 3-methyl-2-(phenylamino)benzoic acids (MPABAs) were synthesized. A preliminary polymorph screen led to one...

Synthesis, Characterization, and Antiproliferative Activity of Novel Chiral [QuinoxP*AuCl2]+ Complexes

Herein is reported the synthesis of two Au(III) complexes bearing the (R,R)-(-)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (R,R-QuinoxP*) or (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (S,S-QuinoxP*) ligands. By reacting two stoichiometric equivalents of HAuCl4.3H2O to one equivalent of the corresponding QuinoxP* ligand, (R,R)-(-)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (1) and (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) were formed, respectively, in moderate yields. The structure of (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) was further confirmed by X-ray crystallography. The antiproliferative activities of the two compounds were evaluated in a panel of cell lines and exhibited promising results comparable to auranofin and cisplatin with IC50 values between 1.08 and 4.83 µM. It is noteworthy that in comparison to other platinum and ruthenium enantiomeric complexes, the two enantiomers (1 and 2) do not exhibit different cytotoxic effects. The compounds exhibited stability in biologically relevant media over 48 h as well as inert reactivity to excess glutathione at 37 °C. These results demonstrate that the Au(III) atom, stabilized by the QuinoxP* ligand, can provide exciting compounds for novel anticancer drugs. These complexes provide a new scaffold to further develop a robust and diverse library of chiral phosphorus Au(III) complexes.

In Situ Reduction and Functionalization of Polycyclic Quinones

Attempts to functionalize polycyclic quinones using lithium diisopropylamide as a base led to the unexpected formation of acenes. This reaction proceeds by electron transfer from the base to the electron deficient quinone, whose radical anion can react with a variety of electrophiles. Siloxy derivatives synthesized by this method could be easily isolated but showed poor photostability. In situ reduced intermediate generation is a convenient approach to functionalization of oxidatively unstable hydroquinones.

Pictet-Spengler condensations using 4-(2-aminoethyl)coumarins

Androgen-deprivation therapy (ADT) is only a palliative measure, and prostate cancer invariably recurs in a lethal, castration-resistant form (CRPC). Prostate cancer resists ADT by metabolizing weak, adrenal androgens to growth-promoting 5α-dihydrotestosterone (DHT), the preferred ligand for the androgen receptor (AR). Developing small-molecule inhibitors for the final steps in androgen metabolic pathways that utilize 17-oxidoreductases required probes that possess fluorescent groups at C-3 and intact, naturally occurring functionality at C-17. Application of the Pictet-Spengler condensation to substituted 4-(2-aminoethyl)coumarins and 5α-androstane-3-ones furnished spirocyclic, fluorescent androgens at the desired C-3 position. Condensations required the presence of activating C-7 amino or N,N-dialkylamino groups in the 4-(2-aminoethyl)coumarin component of these condensation reactions. Successful Pictet-Spengler condensation, for example, of DHT with 9-(2-aminoethyl)-2,3,6,7-tetrahydro-1H,5H,11H-pyrano[2,3-f]pyrido[3,2,1-ij]quinolin-11-one led to a spirocyclic androgen, (3R,5S,10S,13S,17S)-17-hydroxy-10,13-dimethyl-1,2,2',3',4,5,6,7,8,8',9,9',10,11,12,12',13,13',14,15,16,17-docosahydro-7'H,11'H-spiro-[cyclopenta[a]phenanthrene-3,4'-pyrido[3,2,1-ij]pyrido[4',3':4,5]pyrano[2,3-f]quinolin]-5'(1'H)-one. Computational modeling supported the surrogacy of the C-3 fluorescent DHT analog as a tool to study 17-oxidoreductases for intracrine, androgen metabolism.

Synthesis of mono- and dimethoxylated polychlorinated biphenyl derivatives starting from fluoroarene derivatives

Polychlorinated biphenyls (PCBs) are environmental pollutants implicated in a variety of adverse health effects, including cancer and noncancer diseases in animals and humans. PCBs are metabolized to hydroxylated compounds, and some of these PCB metabolites are more toxic than the parent PCBs. Unfortunately, most PCB metabolites needed for toxicological studies are not available from commercial sources. Moreover, it is challenging to synthesize PCB metabolites because starting materials with suitable substitution patterns are not readily available. Here, we report the novel synthesis of a variety of mono- and dimethoxyarene derivatives from commercially available fluoroarenes via nucleophilic aromatic substitution with sodium methoxide. This reaction provided good to excellent yields of the desired methoxylated products. Suzuki coupling of selected mono- and dimethoxy haloarenes with chlorinated phenylboronic acids yielded methoxylated derivatives of PCB 11, 12, 25, 35, and 36 in low to good yields. Crystal structures of 3,3'-dichloro-2,5-dimethoxy-1,1'-biphenyl and 3',5-dichloro-2,3-dimethoxy-1,1'-biphenyl confirmed the substitution pattern of both compounds. This synthesis strategy provides straightforward access to a range of mono- and dimethoxylated PCB derivatives that were not readily accessible previously.

Improved synthesis of N-ethyl-3,7-bis(trifluoromethyl)phenothiazine

N-Ethyl-3,7-bis(trifluoromethyl)phenothiazine is a highly soluble redox shuttle for overcharge protection in lithium-ion batteries with an oxidation potential of ca. 3.8 V vs. Li^+/0 in carbonate solvents.

A stable, highly oxidizing radical cation

Changes in adiabatic ionization potential and half wave oxidation potential withorthoandparasubstitution on anN-alkylated phenothiazine.

An unusually short inter-molecular N-H⋯N hydrogen bond in crystals of the hemi-hydro-chloride salt of 1-exo-acetamido-pyrrolizidine

The title compound [systematic name: (1R*, 8S)-2-acetamidoocta-hydro-pyrrol-izin-4-ium chloride-N-[(1R, 8S)-hexa-hydro-1H-pyrrolizin-2-yl)acetamide (1/1)], 2(C9H16N2O)·HCl or C9H17N2O+·Cl-·C9H16N2O, arose as an unexpected product when 1-exo-acetamido-pyrrolizidine (AcAP; C9H16N2O) was dissolved in CHCl3. Within the AcAP pyrrolizidine group, the unsubstituted five-membered ring is disordered over two orientations in a 0.897 (5):0.103 (5) ratio. Two AcAP mol-ecules related by a crystallographic twofold axis link to H+ and Cl- ions lying on the rotation axis, thereby forming N-H⋯N and N-H⋯Cl⋯H-N hydrogen bonds. The first of these has an unusually short N⋯N separation of 2.616 (2) Å: refinement of different models against the present data set could not distinguish between a symmetrical hydrogen bond (H atom lying on the twofold axis and equidistant from the N atoms) or static or dynamic disorder models (i.e. N-H⋯N + N⋯H-N). Computational studies suggest that the disorder model is slightly more stable, but the energy difference is very small.

Computationally aided design of a high-performance organic semiconductor: the development of a universal crystal engineering core

Herein, we describe the design and synthesis of a suite of molecules based on a benzodithiophene "universal crystal engineering core". After computationally screening derivatives, a trialkylsilylethyne-based crystal engineering strategy was employed to tailor the crystal packing for use as the active material in an organic field-effect transistor. Electronic structure calculations were undertaken to reveal derivatives that exhibit exceptional potential for high-efficiency hole transport. The promising theoretical properties are reflected in the preliminary device results, with the computationally optimized material showing simple solution processing, enhanced stability, and a maximum hole mobility of 1.6 cm2 V-1 s-1.

Synthesis and crystal structure of 1,3-bis-(4-hy-droxy-phen-yl)-1H-imidazol-3-ium chloride

The title compound, 1,3-bis­(4-hy­droxy­phen­yl)-1H-imidazol-3-ium chloride (IOH·Cl) is a new imidazolium salt with a hy­droxy functionality.

Imidazolium salts are common building blocks for functional materials and in the synthesis of N-heterocyclic carbene (NHC) as σ-donor ligands for stable metal complexes. The title salt, 1,3-bis­(4-hy­droxy­phen­yl)-1H-imidazol-3-ium chloride (IOH·Cl), C₁₅H₁₃N₂O₂⁺·Cl⁻, is a new imidazolium salt with a hy­droxy functionality. The synthesis of IOH·Cl was achieved in high yield via a two-step procedure involving a di­aza­butadiene precursor followed by ring closure using tri­methylchloro­silane and paraformaldehyde. The structure of IOH·Cl consists of a central planar imidazolium ring (r.m.s. deviation = 0.0015 Å), with out-of-plane phenolic side arms. The dihedral angles between the 4-hy­droxy­phenyl substituents and the imidazole ring are 55.27 (7) and 48.85 (11)°. In the crystal, O—H⋯Cl hydrogen bonds connect the distal hy­droxy groups and Cl⁻ anions in adjacent asymmetric units, one related by inversion (−x + 1, −y + 1, −z + 1) and one by the n-glide (x − , −y + , z − ), with donor–acceptor distances of 2.977 (2) and 3.0130 (18) Å, respectively. The phenolic rings are each π–π stacked with their respective inversion-related [(−x + 1, −y + 1, −z + 1) and (−x, −y + 1, −z + 1)] counterparts, with inter­planar distances of 3.560 (3) and 3.778 (3) Å. The only other noteworthy inter­molecular inter­action is an O⋯O (not hydrogen bonded) close contact of 2.999 (3) Å between crystallographically different hy­droxy O atoms on translationally adjacent mol­ecules (x + 1, y, x + 1).

Crystal structure of zymonic acid and a redetermination of its precursor, pyruvic acid

Inter­molecular inter­actions in both crystal structures are dominated by hydrogen bonding. The common (8) hydrogen-bonding motif links carb­oxy­lic acid groups on adjacent mol­ecules in both structures.

The structure of zymonic acid (systematic name: 4-hy­droxy-2-methyl-5-oxo-2,5-di­hydro­furan-2-carb­oxy­lic acid), C₆H₆O₅, which had previously eluded crystallographic determination, is presented here for the first time. It forms by intra­molecular condensation of parapyruvic acid, which is the product of aldol condensation of pyruvic acid. A redetermination of the crystal structure of pyruvic acid (systematic name: 2-oxo­propanoic acid), C₃H₄O₃, at low temperature (90 K) and with increased precision, is also presented [for the previous structure, see: Harata et al. (1977 ▸). Acta Cryst. B33, 210–212]. In zymonic acid, the hy­droxy­lactone ring is close to planar (r.m.s. deviation = 0.0108 Å) and the dihedral angle between the ring and the plane formed by the bonds of the methyl and carb­oxy­lic acid carbon atoms to the ring is 88.68 (7)°. The torsion angle of the carb­oxy­lic acid group relative to the ring is 12.04 (16)°. The pyruvic acid mol­ecule is almost planar, having a dihedral angle between the carb­oxy­lic acid and methyl-ketone groups of 3.95 (6)°. Inter­molecular inter­actions in both crystal structures are dominated by hydrogen bonding. The common R₂²(8) hydrogen-bonding motif links carb­oxy­lic acid groups on adjacent mol­ecules in both structures. In zymonic acid, this results in dimers about a crystallographic twofold of space group C2/c, which forces the carb­oxy­lic acid group to be disordered exactly 50:50, which scrambles the carbonyl and hydroxyl groups and gives an apparent equalization of the C—O bond lengths [1.2568 (16) and 1.2602 (16) Å]. The other hydrogen bonds in zymonic acid (O—H⋯O and weak C—H⋯O), link mol­ecules across a 2₁-screw axis, and generate an R₂²(9) motif. These hydrogen-bonding inter­actions propagate to form extended pleated sheets in the ab plane. Stacking of these zigzag sheets along c involves only van der Waals contacts. In pyruvic acid, inversion-related mol­ecules are linked into R₂²(8) dimers, with van der Waals inter­actions between dimers as the only other inter­molecular contacts.

Directed Functionalization Tailors the Polarized Emission and Waveguiding Properties of Anthracene-Based Molecular Crystals

Organic semiconducting crystals are characterized by anisotropic optical and electronic properties, which can be tailored by controlling the packing of the constituent molecules in the crystal unit cell. Here, the synthesis, structural characterization, and emission of anthracene derivatives are focused to correlate directed functionalization and optical properties. These compounds are easily and scalably prepared by standard synthesis techniques, and alterations in functional groups yield materials with either exclusive edge-to-face or face-to-face solid-state interactions. The resulting crystals feature either platelet or needle shapes, and the emission exhibits polarization ratios up to 5 at room temperature. In needle-shaped crystals, self-waveguiding of the emission is also observed with propagation loss coefficients as low as 1.3 dB mm^-1. Moreover, optical coupling between crossing crystalline microwires is found and characterized. The combination of optical anisotropy and emission self-waveguiding opens interesting routes for the exploitation of these active materials in photonic applications, including optical integrated circuits and microscale light sources.

Absolute configuration of 2,2',3,3',6-pentachlorinatedbiphenyl (PCB 84) atropisomers

Nineteen polychlorinated biphenyl (PCB) congeners, such as 2,2',3,3',6-pentachlorobiphenyl (PCB 84), display axial chirality because they form stable rotational isomers, or atropisomers, that are non-superimposable mirror images of each other. Although chiral PCBs undergo atropselective biotransformation and atropselectively alter biological processes, the absolute structure of only a few PCB atropisomers has been determined experimentally. To help close this knowledge gap, pure PCB 84 atropisomers were obtained by semi-preparative liquid chromatography with two serially connected Nucleodex β-PM columns. The absolute configuration of both atropisomers was determined by X-ray single-crystal diffraction. The PCB 84 atropisomer eluting first and second on the Nucleodex β-PM column correspond to (aR)-(-)-PCB 84 and (aS)-(+)-PCB 84, respectively. Enantioselective gas chromatographic analysis with the β-cyclodextrin-based CP-Chirasil-Dex CB gas chromatography column showed the same elution order as the Nucleodex β-PM column. Based on earlier reports, the atropisomers eluting first and second on the BGB-172 gas chromatography column are (aR)-(-)-PCB 84 and (aS)-(+)-PCB 84, respectively. An inversion of the elution order is observed on the Cyclosil-B gas chromatography and Cellulose-3 liquid chromatography columns. These results advance the interpretation of environmental and human biomonitoring as well as toxicological studies.

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.

Photophysical characterization and time-resolved spectroscopy of a anthradithiophene dimer: exploring the role of conformation in singlet fission

Quantitative singlet fission has been observed for a variety of acene derivatives such as tetracene and pentacene, and efforts to extend the library of singlet fission compounds is of current interest. Preliminary calculations suggest anthradithiophenes exhibit significant exothermicity between the first optically-allowed singlet state, S₁, and 2 × T₁ with an energy difference of >5000 cm^-1. Given the fulfillment of this ingredient for singlet fission, here we investigate the singlet fission capability of a difluorinated anthradithiophene dimer (2ADT) covalently linked by a (dimethylsilyl)ethane bridge and derivatized by triisobutylsilylethynyl (TIBS) groups. Photophysical characterization of 2ADT and the single functionalized ADT monomer were carried out in toluene and acetone solution via absorption and fluorescence spectroscopy, and their photo-initiated dynamics were investigated with time-resolved fluorescence (TRF) and transient absorption (TA) spectroscopy. In accordance with computational predictions, two conformers of 2ADT were observed via fluorescence spectroscopy and were assigned to structures with the ADT cores trans or cis to one another about the covalent bridge. The two conformers exhibited markedly different excited state deactivation mechanisms, with the minor trans population being representative of the ADT monomer showing primarily radiative decay, while the dominant cis population underwent relaxation into an excimer geometry before internally converting to the ground state. The excimer formation kinetics were found to be solvent dependent, yielding time constants of ∼1.75 ns in toluene, and ∼600 ps in acetone. While the difference in rates elicits a role for the solvent in stabilizing the excimer structure, the rate is still decidedly long compared to most singlet fission rates of analogous dimers, suggesting that the excimer is neither a kinetic nor a thermodynamic trap, yet singlet fission was still not observed. The result highlights the sensitivity of the electronic coupling element between the singlet and correlated triplet pair states, to the dimer conformation in dictating singlet fission efficiency even when the energetic requirements are met.

Tuning DNA Condensation with Zwitterionic Polyamidoamine (zPAMAM) Dendrimers

Cationic dendrimers are promising vectors for non-viral gene 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 is 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.

Understanding the Crystal Packing and Organic Thin-Film Transistor Performance in Isomeric Guest-Host Systems

In order to understand how additives influence the structure and electrical properties of active layers in thin-film devices, a compositionally identical but structurally different guest-host system based on the syn and anti isomers of triethylsilylethynyl anthradithiophene (TES ADT) is systematically explored. The mobility of organic thin-film transistors (OTFTs) comprising anti TES ADT drops with the addition of only 0.01% of the syn isomer and is pinned at the mobility of OTFTs having pure syn isomer after the addition of only 10% of the isomer. As the syn isomer fraction increases, intermolecular repulsion increases, resulting in a decrease in the unit-cell density and concomitant disordering of the charge-transport pathway. This molecular disorder leads to an increase in charge trapping, causing the mobility of OTFTs to drop with increasing syn-isomer concentration. Since charge transport is sensitive to even minute fractions of molecular disorder, this work emphasizes the importance of prioritizing structural compatibility when choosing material pairs for guest-host systems.

Carbonic anhydrase mimics for enhanced CO2 absorption in an amine-based capture solvent

Carbonic anhydrase converts CO₂ to HCO₃⁻ in physiological conditions, but in the highly basic amine-containing solutions used industrially for carbon capture, the enzyme does not function. Instead small molecule mimics can catalyze CO₂ hydration.

Bulky end-capped [1]benzothieno[3,2-b]benzothiophenes: reaching high-mobility organic semiconductors by fine tuning of the crystalline solid-state order

A series of bulky end-capped [1]benzothieno[3,2-b]benzothiophenes (BTBTs) are developed in order to tune the packing structure via terminal substitution. A coupled theoretical and experimental study allows us to identify 2,7-di-tert-butylBTBT as a new high-performance organic semiconductor with large and well-balanced transfer integrals, as evidenced by quantum-chemical calculations. Single-crystal field-effect transistors show a remarkable average saturation mobility of 7.1 cm(2) V(-1) s(-1) .

Difluorinated 6,13-Bis(triisopropylsilylethynyl)pentacene: Synthesis, Crystallinity, and Charge-Transport Properties

Fluorination has been demonstrated to improve stability and processing in thiophene-containing small-molecule semiconductors. Here, the impact of partial fluorination on these parameters in a pentacene derivative is examined. Although the improvement in photostability is not as dramatic, there is a clear improvement in the stability of the chromophore upon fluorination. The improvement in processability is more dramatic; devices formed by spin-coating with the fluorinated derivative perform substantially better than those formed from the nonfluorinated compound.

Scalable synthesis of 5,11-diethynylated indeno[1,2-b]fluorene-6,12-diones and exploration of their solid state packing

We report a new synthetic route to 5,11-disubstituted indeno[1,2-b]fluorene-6,12-diones that is amenable to larger scale reactions, allowing for the preparation of gram amounts of material. With this new methodology, we explored the effects on crystal packing morphology for the indeno[1,2-b]fluorene-6,12-diones by varying the substituents on the silylethynyl groups.

Structural Investigations on Mono- and Di-Acrolein Substituted Ni(II) Porphyrins and a Ni(II) Benzochlorin. Model Compounds for Photosensitizers in Photodynamic Therapy

The structures of four Ni complexes and a free base related to tetrapentanoporphyrin (TC7P) and octaethylporphyrin (OEP) have been determined by X-ray crystallograpic methods. The Ni(II) complexes exhibit considerable S4-ruffling induced by coordination hole contraction due to the low spin Ni(II). The degree of conformational distortion is enhanced by one or two additional acrolein substituents at the meso positions. The steric strain imposed by interaction of the meso substituent with the neighboring β-pyrrole substituents leads to a significant displacement from the mean plane of the molecule of the meso carbon(s) involved. Increasing non-planarity of the macrocycles is correlated with shifts to longer wavelenghts in the absorption spectra. Ring closures of the acrolein group to afford benzochlorin type pigments results in further bathochromic shifts and a very non-planar molecular conformation. Long wavelength absorbing pigments such as benzochlorins are useful photosensitizers for photodynamic therapy and thus one criterion for a good photosensitizer might be its conformational distortion. Crystal data – 3. C40H46N4 · CH2Cl2, Mr = 667.7, triclinic, P1̄, a = 7.776(5)Å, b = 8.556(4)Â, c = 14.509(8)Å, α = 73.96(1)°, β = 82.04(2)°, γ = 82.58(2)°, V = 914.5(9)Å3, Ζ = 1, Dx = 1.212 Mg/m3, (ΜοΚα) λ = 0.71069Å, μ = 0.209 mm-1, F(000) = 356, 130 Κ, R = 0.082 for 2217 reflections with I > 1.5σ(Ι). Ni4. C44H40N4NiO · CH2Cl2, Mr = 770.4, triclinic, P1̄, a = 11.283(3)Å, b = 11.800(4)Å, c = 15.871(7)Å, α = 79.28(3)°, β = 88.95(2)°, γ = 62.41(1)°, V = 1838.8(11)Å3, Ζ = 2, Dx = 1.391 Mg/m3, (ΜοΚα), μ = 0.715 mm-1, F(000) = 804, 130 Κ, R = 0.072 for 5309 reflections with I > 2.0σ(Ι). Ni5. C46H28N4NiO2 • CH2CH2, Mr = 812.4, triclinic, P1̄, a = 8.959(4)Å, b = 14.420(7)A, c = 15.471(5)Å, α = 102.73(4)°, β = 101.83(4)°, γ = 92.01(5)°, V = 1901.3(14)Å3, Z = 2, Dx = 1.419 Mg/m3, (ΜοΚα), μ = 0.679 mm-1, F(000) = 836, 130 Κ, R = 0.059 for 4197 reflections with I > 1.75σ(Ι). Ni7. C43H45N4NiO2·CH2Cl2, Mr = 793.5, triclinic, P1̄, a = 8.948(3)Å, b = 13.855(3)Å, c = 15.451(3)Å, α = 82.43(2)°, β = 78.79(2)°, γ = 81.24(2)°, V = 1846.7(8)Å3, Z = 2, Dx = 1.427 Mg/m3, (CuKa) λ = 1.54178 Å, μ = 2.448 mm-1, F(000) = 834, 126 K, R = 0.09 for 4039 reflections with I > 2.0σ(Ι). Ni8. C42H48N4NiO, Mr = 683.6, monoclinic, Ρ21/n, a = 15.168(6)Å, b = 14.796(3)Å, c = 15.983(4)Å, β= 97.17(3)°, V = 3552(2)Å3, Z = 4, Dxx = 1.278 Mg/m3, (ΜοΚα), μ = 0.584 mm-1, F(000) = 1456, 130 Κ, R = 0.042 for 5904 reflections with I > 2.5 σ(I).

Intermolecular forces between low generation PAMAM dendrimer condensed DNA helices: role of cation architecture

In recent years, dendriplexes, complexes of cationic dendrimers with DNA, have become attractive DNA delivery vehicles due to their well-defined chemistries. To better understand the nature of the forces condensing dendriplexes, we studied low generation poly(amidoamine) (PAMAM) dendrimer-DNA complexes and compared them to comparably charged linear arginine peptides. Using osmotic stress coupled with X-ray scattering, we have investigated the effect of molecular chain architecture on DNA-DNA intermolecular forces that determine the net attraction and equilibrium interhelical distance within these polycation condensed DNA arrays. In order to compact DNA, linear cations are believed to bind in DNA grooves and to interact with the phosphate backbone of apposing helices. We have previously shown a length dependent attraction resulting in higher packaging densities with increasing charge for linear cations. Hyperbranched polycations, such as polycationic dendrimers, presumably would not be able to bind to DNA and correlate their charges in the same manner as linear cations. We show that attractive and repulsive force amplitudes in PAMAM-DNA assemblies display significantly different trends than comparably charged linear arginines resulting in lower DNA packaging densities with increasing PAMAM generation. The salt and pH dependencies of packaging in PAMAM dendrimer-DNA and linear arginine-DNA complexes were also investigated. Significant differences in the force curve behaviour and salt and pH sensitivities suggest that different binding modes may be present in DNA condensed by dendrimers when compared to linear polycations.

Improving carbon capture from power plant emissions with zinc- and cobalt-based catalysts

A carbonic anhydrase mimic converting CO₂ to carbonic acid, deprotonated under highly basic conditions, and being converted to a carbamate upon reaction with monoethanolamine, a solvent reported for carbon capture reactions.

High mobility field-effect transistors with versatile processing from a small-molecule organic semiconductor

Trialkylgermyl functionalization allows the development of high-performance soluble small-molecule organic semiconductors with mobilities greater than 5 cm(2) V(-1) s(-1) . Spray-deposited organic thin-film transistors show a record mobility of 2.2 cm(2) V(-1) s(-1) and demonstrate the potential for incorporation in large-area, low-cost electronic applications.