Sergio Granados-Focil

From computational discovery to experimental characterization of a high hole mobility organic crystal

For organic semiconductors to find ubiquitous electronics applications, the development of new materials with high mobility and air stability is critical. Despite the versatility of carbon, exploratory chemical synthesis in the vast chemical space can be hindered by synthetic and characterization difficulties. Here we show that in silico screening of novel derivatives of the dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene semiconductor with high hole mobility and air stability can lead to the discovery of a new high-performance semiconductor. On the basis of estimates from the Marcus theory of charge transfer rates, we identified a novel compound expected to demonstrate a theoretic twofold improvement in mobility over the parent molecule. Synthetic and electrical characterization of the compound is reported with single-crystal field-effect transistors, showing a remarkable saturation and linear mobility of 12.3 and 16 cm2 V−1 s−1, respectively. This is one of the very few organic semiconductors with mobility greater than 10 cm2 V−1 s−1 reported to date.

Robust and Ultrasensitive Polymer Membrane-Based Carbonate-Selective Electrodes.

Quantitative analysis of the carbonate species within clinical and environmental samples is highly critical to the advancement of accurate environmental monitoring, disease screening, and personalized medicine. Herein we report the first example of carbonate detection using ultrasensitive ion selective electrodes (ISEs). The low detection limit (LDL) of these electrodes was at least 4 orders of magnitude lower than the best currently existing carbonate sensors. This was achieved by a simple alteration of the sensors conditioning protocol. This resulted in the reduction of ion fluxes across the membrane interface consequently lowering the LDL to picomolar levels. The proposed ISEs exhibited near-Nernstian potentiometric responses to carbonate ions with a detection limit of 80 pmol L(-1) (5 ppt) and was utilized for direct determination of carbonate in seawater. Moreover, the new methodology has produced electrodes with excellent reproducibility, robustness, and durability. It is anticipated that this approach may form the basis for the development of highly sensitive and robust ion selective electrodes capable of in situ measurements.

Nanostructured ion gels from liquid crystalline block copolymers and gold nanoparticles in ionic liquids: manifestation of mechanical and electrochemical properties

We examine the influence of confining gold nanoparticles on the overall nanoscale morphology, mechanical and electrochemical properties of nanocomposite ion gels. Stimuli-responsive ion gels are generated via the synthesis of gold nanoparticles (AuNPs) within a thiol-functionalized liquid crystalline brush-like block copolymer (LCBBC) and subsequent gelation in ionic liquids. AuNPs are prepared by in situ reduction of the gold ions and stabilized by direct anchoring through coordination bonds with the thiol-functionalized LCBBC. The resulting LCBBC/AuNP nanocomposite comprises a hierarchical structure in which polymer-coated AuNPs are dispersed in a microsegregated LCBBC matrix that further contains both liquid crystalline (LC) and block copolymer ordering. More importantly, this LCBBC/AuNP nanocomposite is solubilized in an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, to form a nanocomposite ion gel. At 5 wt% concentration, LCBBC/AuNP nanocomposite ion-gel exhibits interesting characteristics including excellent mechanical strength (∼103 Pa), good optical properties with higher ionic conductivity (∼10−2 S cm−1) and long-term electrochemical stability over a larger potential range compared to the plain LCBBC ion gel. Thus, nanocomposite ion gels present tunable optical, thermal and mechanical properties by virtue of their polymer architecture, morphology and functionality. These are versatile and modular hybrid materials to design nanocomposite ion gels with multiple functionalities for applications in electrochemical devices, photonics, and opto-electronics.

Synthesis and Characterization of Triazolium Iodide Ionic Liquid Electrolyte for Dye Sensitized Solar Cells

Imidazolium iodide compounds have been utilized in the electrolytes for dye sensitized solar cells (DSSC). Most of the investigations with these compounds focus on the formulation of eutectic mixtures that promote efficient dissociation and diffusion of the iodide and triiodide species. Facile alternative synthetic approaches such as click chemistry (Huisgen 3+2 dipolar cycloaddition reaction) can be utilized to broaden the scope of electrochemically stable promising materials for novel electrolyte systems. Here, we report the first example of a triazolium functionalized cyclic siloxane that can be used as an electrolyte component in solvent-based DSSCs. The devices fabricated with this new triazolium salt in the electrolyte yielded short circuit current densities (26 mA/cm2), as well as power conversion efficiencies of 8%, these values are comparable to those obtained for imidazolium salt analogues.

Triazole Functionalized Sol-Gel Membranes, Effect of Crosslink Density and Heterocycle Content on Water Free Proton Conduction and Membrane Mechanical Properties

Freestanding, ion conducting, membranes were synthesized by incorporating triazole-containing tetracyclosiloxanes into a polyethylene glycol-tetraethyl orthosilicate (PEG-TEOS) based sol-gel matrix. These membranes show comparable or higher proton conductivities than their linear, liquid, polysiloxane analogs and fall within an order of magnitude of the target ion mobilities for use in proton exchange membrane fuel cells (PEMFCs). The absence of any unbound PEG or cyclic siloxane was confirmed by proton nuclear magnetic resonance (1H-NMR), while the chemical structure and composition of the membranes was corroborated by Fourier transform infrared (FTIR) spectroscopy. Thermogravimetric analysis (TGA) indicated that the membranes are stable up to 180°C and differential scanning calorimetry (DSC) analysis showed complete suppression of PEG crystallization after incorporation of the triazole-functionalized cyclosiloxanes. An increase in the molecular weight of the PEG chains used to create the sol-gel matrix produced membranes with increased flexibility and higher proton conductivities at temperatures below 100 °C. Pulse field gradient echo (PFG) NMR studies showed an increase in the apparent diffusion coefficient of the sol-gel threaded cyclosiloxane motifs compared to the linear polysiloxanes, indicating a significant reduction on the coupling between mechanical strength and ion transport capability.