Combination of Counterion Size and Doping Concentration Determines the Electronic and Thermoelectric Properties of Semiconducting Polymers.

In both chemical and electrochemical doping of organic semiconductors (OSCs), a counterion, either from the electrolyte or ionized dopant, balances the charge introduced to the OSC. Despite the large influence of this counterion on OSC optical and electronic response, there remains substantial debate on how a fundamental parameter, ion size, impacts these properties. This work resolves much of this debate by accounting for two doping regimes. In the low-doping regime, the Coulomb binding energies between charge carriers on the OSC and the counterions are significant, and larger counterions lead to decreased Coulomb interactions, more delocalized charge carriers, and higher electrical conductivities. In the high-doping regime, the Coulomb binding energies become negligible due to the increased dielectric constant of the films and a smoothing of the energy landscape; thereby, the electrical conductivities depend primarily on the extent of morphological disorder in the OSC. Moreover, in regioregular poly(3-hexylthiophene), rr-P3HT, smaller counterions lead to greater bipolaron concentrations in the low-doping regime due to the increased Coulomb interactions. Emphasizing the impact of the counterion size, it is shown that larger counterions can lead to increased thermoelectric power factors for rr-P3HT.

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.

Triarylphosphine-Coordinated Bipyridyl Ru(II) Complexes Induce Mitochondrial Dysfunction.

While cancer cells rely heavily upon glycolysis to meet their energetic needs, reducing the importance of mitochondrial oxidative respiration processes, more recent studies have shown that their mitochondria still play an active role in the bioenergetics of metastases. This feature, in combination with the regulatory role of mitochondria in cell death, has made this organelle an attractive anticancer target. Here, we report the synthesis and biological characterization of triarylphosphine-containing bipyridyl ruthenium (Ru(II)) compounds and found distinct differences as a function of the substituents on the bipyridine and phosphine ligands. 4,4'-Dimethylbipyridyl-substituted compound 3 exhibited especially high depolarizing capabilities, and this depolarization was selective for the mitochondrial membrane and occurred within minutes of treatment in cancer cells. The Ru(II) complex 3 exhibited an 8-fold increase in depolarized mitochondrial membranes, as determined by flow cytometry, which compares favorably to the 2-fold increase observed by carbonyl cyanide chlorophenylhydrazone (CCCP), a proton ionophore that shuttles protons across membranes, depositing them into the mitochondrial matrix. Fluorination of the triphenylphosphine ligand provided a scaffold that maintained potency against a range of cancer cells but avoided inducing toxicity in zebrafish embryos at higher concentrations, displaying the potential of these Ru(II) compounds for anticancer applications. This study provides essential information regarding the role of ancillary ligands for the anticancer activity of Ru(II) coordination compounds that induce mitochondrial dysfunction.

Structure and Piezoelectricity Due to B Site Cation Variation in ABn+Cln+2 Hybrid Histammonium Chlorometallate Materials.

To provide new insights for understanding the influence of B site cations on the structure in chlorometallate materials of the form ABn+Cln+2, we report novel organic-inorganic hybrid metallates (OIHMs) incorporating histammonium (HistNH3) dications and various transition-metal and main group B site cations. Single crystals of OIHMs with the basic formula (HistNH3Mn+Cln+2, M = Fe, Co, Ni, Cu, Zn, Cd, Hg, Sb, Sn, Pb, Bi) were grown and their structures characterized by single-crystal X-ray crystallography. HistNH3CoCl4, HistNH3ZnCl4, and HistNH3SbCl5 were crystallized in a non-centrosymmetric space group and were subsequently studied with piezoresponse force microscopy (PFM). While bulk measurements of crystals and poly(vinylidene difluoride) (PVDF)/metallate composite films exhibited low bulk response values, the surface-measured local response values using PFM were 5.17 pm/V for HistNH3CoCl4, 22.6 pm/V for HistNH3ZnCl4, and 2.9 pm/V for HistNH3SbCl5 compared with 2.50 pm/V for PVDF reference samples. The magnitudes of the d33 coefficient, net dipole, and cation-Cl bond dipole obtained from the density functional theory calculations confirm the higher response in HistNH3ZnCl4 compared to HistNH3CoCl4. Density of states and crystal orbital Hamilton population analysis indicate that the higher net dipole in HistNH3ZnCl4 compared to HistNH3CoCl4 is due to the lower hybridization of the M-Cl bond.

Development of branched polyphenolic poly(beta amino esters) to facilitate post-synthesis processing.

Given their versatility and formability, polymers have proven to be a viable platform facilitating a controlled and tuned release for a variety of therapeutic agents. One growing area of polymer drug delivery is polymeric prodrugs, which covalently link active pharmaceutical ingredients to a polymeric form to enhance stability, delivery, and pharmacology. One such class of polymeric prodrugs, poly(beta amino esters) (PßAEs) can be synthesized into crosslinked, or "thermoset," networks which greatly limits their processability. An antioxidant-PßAE polymer prodrug that is soluble in organic solutions would permit enhanced processability, increasing their utility and manufacturability. Curcumin PßAEs were synthesized to be soluble in organic solvents while retaining the release and activity properties. To demonstrate the polymer processability, curcumin PßAEs were further synthesized into nanoparticles and thin films. Control over nanoparticle size and film thickness was established through variance of dope solution concentration and withdrawal speed, respectively. Layering of polymeric films was demonstrated through inkjet printing of thin films. Polymer function was characterized through curcumin release and antioxidant activity. The processing of the polymer had a drastic impact on the curcumin release profiles indicating the polymer degradation was influenced by surface area and porosity of the final product. Previously, release was controlled primarily through the hydrophobicity of the polymer. Here, we demonstrate a novel method for further tuning the degradation by processing the polymer.

Preserving Porosity of Mesoporous Metal-Organic Frameworks through the Introduction of Polymer Guests.

High internal surface areas, an asset that is highly sought after in material design, has brought metal-organic frameworks (MOFs) to the forefront of materials research. In fact, a major focus in the field is on creating innovative ways to maximize MOF surface areas. Despite this, large-pore MOFs, particularly those with mesopores, continue to face problems with pore collapse upon activation. Herein, we demonstrate an easy method to inhibit this problem via the introduction of small quantities of polymer. For several mesoporous, isostructural MOFs, known as M2(NDISA) (where M = Ni2+, Co2+, Mg2+, or Zn2+), the accessible surface areas are increased dramatically, from 5 to 50 times, as the polymer effectively pins the MOFs open. Postpolymerization, the high surface areas and crystallinity are now readily maintained after heating the materials to 150 °C under vacuum. These activation conditions, which could not previously be attained due to pore collapse, also provide accessibility to high densities of open metal coordination sites. Molecular simulations are used to provide insight into the origin of instability of the M2(NDISA) series and to propose a potential mechanism for how the polymers immobilize the linkers, improving framework stability. Last, we demonstrate that the resulting MOF-polymer composites, referred to as M2(NDISA)-PDA, offer a perfect platform for the appendage/immobilization of small nanocrystals inside rendering high-performance catalysts. After decorating one of the composites with Pd (average size: 2 nm) nanocrystals, the material shows outstanding catalytic activity for Suzuki-Miyaura cross-coupling reactions.

Efficient Planar Perovskite Solar Cells Using Passivated Tin Oxide as an Electron Transport Layer.

Planar perovskite solar cells using low-temperature atomic layer deposition (ALD) of the SnO2 electron transporting layer (ETL), with excellent electron extraction and hole-blocking ability, offer significant advantages compared with high-temperature deposition methods. The optical, chemical, and electrical properties of the ALD SnO2 layer and its influence on the device performance are investigated. It is found that surface passivation of SnO2 is essential to reduce charge recombination at the perovskite and ETL interface and show that the fabricated planar perovskite solar cells exhibit high reproducibility, stability, and power conversion efficiency of 20%.

Bis(arylimidazole) Iridium Picolinate Emitters and Preferential Dipole Orientation in Films.

The straightforward synthesis and photophysical properties of a new series of heteroleptic iridium(III) bis(2-arylimidazole) picolinate complexes are reported. Each complex has been characterized by nuclear magnetic resonance, UV-vis, cyclic voltammetry, and photoluminescent angle dependency, and the emissive properties of each are described. The preferred orientation of transition dipoles in emitter/host thin films indicated more preferred orientation than homoleptic complex Ir(ppy)3.

Approaches for Selective Synthesis of Ullazine Donor-Acceptor Systems.

Methods for effective synthesis for the four possible isomeric 3,9-diphenylullazine carboxaldehydes and reactive halogen intermediates are described. Ullazine donor-acceptor (D-A) dyes were studied using UV/Vis, photoluminescence (PL) spectroscopy and cyclic voltammetry. X-ray single crystal diffraction analysis independently confirmed the structures of two key intermediates. A D-A dye based on ullazine with dihexylmalonate acceptor was tested as a dopant-free hole-transporting material (HTM) in a perovskite solar cell, exhibiting promising power conversion efficiency (PCE) reaching 13.07 %.

Indolizine-Squaraines: NIR Fluorescent Materials with Molecularly Engineered Stokes Shifts.

The development of deep red and near infrared emissive materials with high quantum yields is an important challenge. Several classes of squaraine dyes have demonstrated high quantum yields, but require significantly red-shifted absorptions to access the NIR window. Additionally, squaraine dyes have typically shown narrow Stokes shifts, which limits their use in living biological imaging applications due to dye emission interference with the light source. Through the incorporation of indolizine heterocycles we have synthesized novel indolizine squaraine dyes with increased Stokes shifts (up to >0.119 eV, >50 nm increase) and absorptions substantially further into the NIR region than an indoline squaraine benchmark (726 nm versus 659 nm absorption maxima). These materials have shown significantly enhanced water solubility, which is unique for squaraine dyes without water-solubilizing substituents. Absorption, electrochemical, computational, and fluorescence studies were undertaken and exceptional fluorescence quantum yields of up 12 % were observed with emission curves extending beyond 850 nm.

Phosphorescent Neutral Iridium (III) Complexes for Organic Light-Emitting Diodes.

The development of transition metal complexes for application in light-emitting devices is currently attracting significant research interest. Among phosphorescent emitters, those involving iridium (III) complexes have proven to be exceedingly useful due to their relatively short triplet lifetime and high phosphorescence quantum yields. The emission wavelength of iridium (III) complexes significantly depends on the ligands, and changing the electronic nature and the position of the ligand substituents can control the properties of the ligands. In this chapter, we discuss recent developments of phosphorescent transition metal complexes for organic light-emitting diode applications focusing solely on the development of iridium metal complexes.

Molecular Design Principles for Near-Infrared Absorbing and Emitting Indolizine Dyes.

Desirable components for dye-sensitzed solar cell (DSC) sensitizers and fluorescent imaging dyes include strong donating building blocks coupled with well-balanced acceptor functionalities for absorption beyond the visible range. We have evaluated the effects of increasing acceptor strengths and incorporation of dye morphology controlling groups on molar absorptivity and absorption breadth with indolizine donor-based dyes. Indolizine-based D-A and D-π-A sensitizers incorporating bis-rhodanine, tricyanofuran (TCF), and cyanoacrylic acid functionalities were analyzed for performance in DSC devices. The TCF derivatives were also evaluated as near-infrared (NIR)-emissive materials with the AH25 emissions extending past 1000 nm.

Molecularly Engineered Ru(II) Sensitizers Compatible with Cobalt(II/III) Redox Mediators for Dye-Sensitized Solar Cells.

Thiocyanate-free isoquinazolylpyrazolate Ru(II) complexes were synthesized and applied as sensitizers in dye-sensitized solar cells (DSCs). Unlike most other successful Ru sensitizers, Co-based electrolytes were used, and resulting record efficiency of 9.53% was obtained under simulated sunlight with an intensity of 100 mW cm(-2). Specifically, dye 51-57dht.1 and an electrolyte based on Co(phen)3 led to measurement of a JSC of 13.89 mA cm(-2), VOC of 900 mV, and FF of 0.762 to yield 9.53% efficiency. The improved device performances were achieved by the inclusion of 2-hexylthiophene units onto the isoquinoline subunits, in addition to lengthening the perfluoroalkyl chain on the pyrazolate chelating group, which worked to increase light absorption and decrease recombination effects when using the Co-based electrolyte. As this study shows, Ru(II) sensitizers bearing sterically demanding ligands can allow successful utilization of important Co electrolytes and high performance.

A low recombination rate indolizine sensitizer for dye-sensitized solar cells.

A sensitizer incorporating a heavily alkylated surface blocking indolizine donor exhibits excellent light absorption and diminished recombination rates in dye-sensitized solar cells (DSCs). DSC device efficiencies (up to 8%) using either I(-)/I3(-) or Co(bpy)3(2+/3+) redox shuttles were obtained, which compare favourably to the known excellent surface coverage co-sensitization dye, .

Electrocatalytic Reduction of CO2 to CO With Re-Pyridyl-NHCs: Proton Source Influence on Rates and Product Selectivities.

A series of four electron-deficient-substituted Re(I) pyridyl N-heterocyclic carbene (pyNHC) complexes have been synthesized, and their electrocatalytic reduction of CO2 has been evaluated by cyclic voltammetry and controlled potential electrolysis experiments. All of the catalysts were evaluated by cyclic voltammetry under inert atmosphere and under CO2 and compared to the known benchmark catalyst Re(bpy)(CO)3Br. Among the four Re-NHC catalysts, Re(pyNHC-PhCF3)(CO)3Br (2) demonstrated the highest catalytic rate (icat/ip)(2) at the first and second reduction events with a value of 4 at the second reduction potential (TOF = 0.8 s(-1)). The rate of catalysis was enhanced through the addition of proton sources (PhOH, TFE, and H2O; TOF up to 100 s(-1); (icat/ip)(2) = 700). Controlled potential electrolysis shows Faradaic efficiencies (FE) for CO production and accumulated charge for the Re(pyNHC-PhCF3)(CO)3Br catalyst exceed those of the benchmark catalyst in the presence of 2 M H2O (92%, 13 C at 1 h versus 61%, 3 C for the benchmark catalyst) under analogous experimental conditions. A peak FE of 100% was observed during electrolysis with Re(pyNHC-PhCF3)(CO)3Br.

Photocatalytic Reduction of CO2 with Re-Pyridyl-NHCs.

A series of Re(I) pyridyl N-heterocyclic carbene (NHC) complexes have been synthesized and examined in the photocatalytic reduction of CO2 using a simulated solar spectrum. The catalysts were characterized through NMR, UV-vis, cyclic voltammetry under nitrogen, and cyclic voltammetry under carbon dioxide. The complexes were compared directly with a known benchmark catalyst, Re(bpy) (CO)3Br. An electron-deficient NHC substituent (PhCF3) was found to promote catalytic activity when compared with electron-neutral and -rich substituents. Re(PyNHC-PhCF3) (CO)3Br was found to exceed the CO production of the benchmark Re(bpy) (CO)3Br catalyst (51 vs 33 TON) in the presence of electron donor BIH and photosensitizer fac-Ir(ppy)3. Importantly, Re(PyNHC-PhCF3) (CO)3Br was found to function without a photosensitizer (32 TON) at substantially higher turnovers than the benchmark catalyst Re(bpy) (CO)3Br (14 TON) under a solar simulated spectrum.

Au137(SR)56 nanomolecules: composition, optical spectroscopy, electrochemistry and electrocatalytic reduction of CO2.

Au137(SR)56, a nanomolecule with a precise number of metal atoms and ligands, was synthesized. The composition was confirmed by MALDI and ESI mass spectrometry using three unique ligands (-SCH2CH2Ph, -SC6H13, and -SC4H9) and nano-alloys with Ag and Pd. The electrocatalytic properties were tested for CO2 reduction.

An efficient synthesis of bis-1,3-(3'-aryl-N-heterocycl-1'-yl)arenes as CCC-NHC pincer ligand precursors.

A report that demonstrated an efficient methodology for the arylation of imidazoles has been extended to bis(N-heterocyclic) compounds. Using bis(aryl) iodonium salts provides high-yielding access to CCC-NHC ligand precursors in a single step. Examples of arylation using various iodonium salts are reported herein with an investigation into the factors governing their relative rate of reactivity. The metalation of one of these compounds using Zr(NMe2)4 and its subsequent treatment with [Pt(COD)Cl2] to yield a transmetalated product are reported.

Platinum CCC-NHC benzimidazolyl pincer complexes: synthesis, characterization, photostability, and theoretical investigation of a blue-green emitter.

The recently reported metallation/transmetallation route for the synthesis of CCC-bis(NHC) pincer ligand architectures was extended to 1,3-bis(3'-(trimethylsilylmethyl)-benzimidizol-1'-yl)benzene. The precursor was metallated with Zr(NMe2)4 and transmetallated to Pt using [Pt(COD)Cl2]. This Pt complex was found to resist photobleaching under UV irradiation in ambient conditions. Density functional theory (DFT) computations were used to generate the emission spectrum of the complex and reveal that this spectrum is the result of a transition from the triplet excited state (T1) to the ground state (S0). The Pt complex's molecular structure was determined by X-ray crystallography. The UV-vis absorption and emission spectra in solution and the solid-state emission spectra are reported. The solid-state photostability data and the radiative lifetime is also reported.