Ethylene Detection Based on Organic Field-Effect Transistors With Porogen and Palladium Particle Receptor Enhancements

Ethylene sensing is a highly challenging problem for the horticulture industry because of the limited physiochemical reactivity of ethylene. Ethylene plays a very important role in the fruit life cycle and has a significant role in determining the shelf life of fruits. Limited ethylene monitoring capability results in huge losses to the horticulture industry as fruits may spoil before they reach the consumer, or they may not ripen properly. Herein we present a poly­(3-hexylthiophene-2,5-diyl) (P3HT)-based organic field effect transistor as a sensing platform for ethylene with sensitivity of 25 ppm V/V. To achieve this response, we used N-(<i>tert</i>-Butoxy-carbonyloxy)-phthalimide and palladium particles as additives to the P3HT film. N-(<i>tert</i>-Butoxy-carbonyloxy)-phthalimide is used to increase the porosity of the P3HT, thereby increasing the overall sensor surface area, whereas the palladium (<1 μm diameter) particles are used as receptors for ethylene molecules in order to further enhance the sensitivity of the sensor platform. Both modifications give statistically significant sensitivity increases over pure P3HT. The sensor response is reversible and is also highly selective for ethylene compared to common solvent vapors

Molecular Switching via Multiplicity-Exclusive <i>E</i>/<i>Z</i> Photoisomerization Pathways

Mutual exclusivity in the nature of forward and reserve isomerization pathways holds promise for predictably controlling responses of photoswitchable materials according to molecular structure or external stimuli. Herein we have characterized the <i>E</i>/<i>Z</i> photoisomerization mechanisms of the visible-light-triggered switch 1,2-dithienyl-1,2-dicyanoethene (4TCE) in chlorobenzene with ultrafast transient absorption spectroscopy. We observe that switching mechanisms occur exclusively by relaxation through electronic manifolds of different spin multiplicity: <i>trans</i>-to-<i>cis</i> isomerization only occurs via electronic relaxation within the singlet manifold on a time scale of 40 ps; in contrast, <i>cis</i>-to<i>-trans</i> isomerization is not observed above 440 nm, but occurs via two rapid ISC processes into and out of the triplet manifold on time scales of ∼2 ps and 0.4 ns, respectively, when excited at higher energies (e.g., 420 nm). Observation of ultrafast ISC in <i>cis</i>-4TCE is consistent with photoinduced dynamics of related thiophene-based oligomers. Interpretation of the photophysical pathways underlying these isomerization reactions is supported by the observation that <i>cis</i>-to-<i>trans</i> isomerization occurs efficiently via triplet-sensitized energy transfer, whereas <i>trans</i>-to-<i>cis</i> isomerization does not. Quantum-chemical calculations reveal that the T₁ potential energy surface is barrierless along the coordinate of the central ethylene dihedral angle (θ) from the <i>cis</i> Franck–Condon region (θ = 175°) to geometries that are within the region of the <i>trans</i> ground-state well; furthermore, the T₁ and S₁ surfaces cross with a substantial spin–orbital coupling. In total, we demonstrate that <i>E</i>/<i>Z</i> photoswitching of 4TCE operates by multiplicity-exclusive pathways, enabling additional means for tailoring switch performance by manipulating spin–orbit couplings through variations in molecular structure or physical environment

Electrical “Turn-On” Response of Poly(3,3‴-didodecylquaterthiophene) and Electron Donor Blend Transistors to 2,4,6-Trinitrotoluene

Electrical “Turn-On” Response of Poly(3,3‴-didodecylquaterthiophene) and Electron Donor Blend Transistors to 2,4,6-Trinitrotoluen

Solid-Phase Synthesis of Self-Assembling Multivalent π‑Conjugated Peptides

We present a completely solid-phase synthetic strategy to create three- and four-fold peptide-appended π-electron molecules, where the multivalent oligopeptide presentation is dictated by the symmetries of reactive handles placed on discotic π-conjugated cores. Carboxylic acid and anhydride groups were viable amidation and imidation partners, respectively, and oligomeric π-electron discotic cores were prepared through Pd-catalyzed cross-couplings. Due to intermolecular hydrogen bonding between the three or four peptide axes, these π-peptide hybrids self-assemble into robust one-dimensional nanostructures with high aspect ratios in aqueous solution. The preparation of these systems via solid-phase methods will be detailed along with their self-assembly properties, as revealed by steady-state spectroscopy and transmission electron microscopy and electrical characterization using field-effect transistor measurements

Demonstration of Hole Transport and Voltage Equilibration in Self-Assembled π‑Conjugated Peptide Nanostructures Using Field-Effect Transistor Architectures

π-Conjugated peptide materials are attractive for bioelectronics due to their unique photophysical characteristics, biofunctional interfaces, and processability under aqueous conditions. In order to be relevant for electrical applications, these types of materials must be able to support the passage of current and the transmission of applied voltages. Presented herein is an investigation of both the current and voltage transmission activities of one-dimensional π-conjugated peptide nanostructures. Observations of the nanostructures as both semiconducting and gate layers in organic field-effect transistors (OFETs) were made, and the effect of systematic changes in amino acid composition on the semiconducting/conducting functionality of the nanostructures was investigated. These molecular variations directly impacted the hole mobility values observed for the nanomaterial active layers over 3 orders of magnitude (∼0.02 to 5 × 10^–5 cm² V^–1 s^–1) when the nanostructures had quaterthiophene cores and the assembled peptide materials spanned source and drain electrodes. Peptides without the quaterthiophene core were used as controls and did not show field-effect currents, verifying that the transport properties of the nanostructures rely on the semiconducting behavior of the π-electron core and not just ionic rearrangements. We also showed that the nanomaterials could act as gate electrodes and assessed the effect of varying the gate dielectric layer thickness in devices where the conventional organic semiconductor pentacene spanned the source and drain electrodes in a top-contact OFET, showing an optimum performance with 35–40 nm dielectric thickness. This study shows that these peptides that self-assemble in aqueous environments can be used successfully to transmit electronic signals over biologically relevant distances

Correction to Peptide-Based Supramolecular Semiconductor Nanomaterials via Pd-Catalyzed Solid-Phase “Dimerizations”

Correction to Peptide-Based Supramolecular Semiconductor Nanomaterials via Pd-Catalyzed Solid-Phase “Dimerizations

Peptide-Based Supramolecular Semiconductor Nanomaterials via Pd-Catalyzed Solid-Phase “Dimerizations”

We report a streamlined method for the synthesis of peptides embedded with complex and easily variable π-conjugated oligomeric subunits from commercially available precursors. These modified peptides self-assemble under aqueous conditions to form one-dimensional nanomaterials containing networks of π-stacked conduits, despite the inclusion of π-conjugated oligomers with quadrupoles extended over larger areas. The procedure has circumvented solubility and other synthetic issues to allow for the facile formation of a diverse library of bioelectronic nanomaterials, including a complex sexithiophene-containing peptide whose nanostructures display gate-induced conductivity within field effect transistors

Ion Dependence of Gate Dielectric Behavior of Alkali Metal Ion-Incorporated Aluminas in Oxide Field-Effect Transistors

The effect of different alkali metal ions (Li⁺, Na⁺, K⁺) incorporated into aluminas on the gate dielectric behavior of solution processed oxide field-effect transistors (FETs) was studied. High field-effect mobility (ca. 20 cm²·V^–1·s^–1), high saturation drain current (about 1 mA), and low subthreshold swing (ca. 200 mV/decade) were achieved in low-voltage (2 V), spin-coated zinc-tin-oxide (ZTO) FETs with potassium alumina (PA) and lithium alumina (LA) dielectrics, as we had previously demonstrated with sodium alumina (SA). To investigate the effect of alkali metal ion on the detailed alumina capacitance and AC conductivity response, the frequency, temperature, and thickness dependences of alumina capacitance were determined. Ion-incorporated alumina metal–insulator–metal (MIM) capacitors showed a possible electric double layer capacitor (EDLC) behavior, in contrast to what was observed for alumina itself. The frequency dependence of observed capacitance varied with the included ion. These dependences were consistent with expected ion–oxygen atom bonding and numbers of surrounding water molecules. Theoretical calculations gave a proposed structure for the amorphous phase of these aluminas, comprising dense ion-free alumina regions and more open, ion-intercalated channel regions, where ions appear to migrate to the double layer at low frequency and are polarized on short length scales at high frequency. The magnitudes of calculated ion migration activation energies indicate that the ions move through continuous pores or channels, rather than through domains of nonintercalated alumina, and that they migrate in hydrated forms

Tetrathiafulvalene (TTF)-Functionalized Thiophene Copolymerized with 3,3‴-Didodecylquaterthiophene: Synthesis, TTF Trapping Activity, and Response to Trinitrotoluene

We report a synthesis route to a thiophene polymer where the repeat unit consists of 3,3‴-didodecylquaterthiophene (as in PQT12) plus an additional thiophene ring from which other functional groups may be projected. The hydroxymethyl form of this polymer, while only a poor semiconductor in its own right, serves as a vehicle for compatibilizing PQT12 itself with arbitrary functional groups. In this article, we focus on tetrathiafulvalene (TTF) as the functionality. As expected, the TTF group acts as a hole trap, as shown by loss of hole mobility and a surprising negative Seebeck coefficient, but this enables a current-increase response to trinitrotoluene as an analyte and confirms a similar observation we recently reported for a dissolved TTF. Added dopants also fill the trap states, restoring hole mobility and the typical positive Seebeck coefficient

Sensitive and Selective NO₂ Sensing Based on Alkyl- and Alkylthio-Thiophene Polymer Conductance and Conductance Ratio Changes from Differential Chemical Doping

NO₂-responsive polymer-based organic field-effect transistors (OFETs) are described, and room-temperature detection with high sensitivity entirely from the semiconductor was achieved. Two thiophene polymers, poly­(bisdodecylquaterthiophene) and poly­(bisdodecylthioquaterthiophene) (PQT12 and PQTS12, respectively), were used as active layers to detect a concentration at least as low as 1 ppm of NO₂. The proportional on-current change of OFETs using these polymers reached over 400% for PQTS12, which is among the highest sensitivities reported for a NO₂-responsive device based on an organic semiconducting film. From measurements of cyclic voltammetry and the electronic characteristics, we found that the introduction of sulfurs into the side chains induces traps in films of the PQTS12 and also decreases domain sizes, both of which could contribute to the higher sensitivity of PQTS12 to NO₂ gas compared with PQT12. The ratio of responses of PQTS12 and PQT12 is higher for exposures to lower concentrations, making this parameter a means of distinguishing responses to low concentrations for extended times from exposures to high concentrations from shorter times. The responses to nonoxidizing vapors were much lower, indicating good selectivity to NO₂ of two polymers. This work demonstrates the capability of increasing selectivity and calibration of OFET sensors by modulating redox and aggregation properties of polymer semiconductors