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Organic thin-film transistors (OTFTs) have shown promise for a range of sensing applications, with phthalocyanine-based OTFTs demonstrated as sensors for atmospheric parameters, volatile gases, and small organic molecules including cannabinoids. However, the process of fabricating, testing, and optimizing OTFTs in a laboratory setting requires highly specialized equipment, materials, and expertise. To determine if sensor development can be expedited and thus reduce manufacturing burden, spectroelectrochemistry is applied to rapidly screen for molecular interactions between metal-free phthalocyanines and a variety of metal phthalocyanines (MPcs) and the cannabinoids Δ9-tetrahydrocannabinol (THC) or cannabidiol (CBD), with and without a cannabinoid-sensitive chromophore (Fast Blue BB). Spectral analyses are corroborated by 2D-NMR and related to measured OTFT performance. Spectroelectrochemical changes to the Q band region of the phthalocyanine spectra in the presence of analytes can be used to predict the response of OTFTs. Thus, with spectroelectrochemistry, a range of potential materials for OTFT small organic molecule-sensing applications can be quickly analyzed, and phthalocyanines with a preferred response can be selected.

Quality control is imperative for Cannabis since the primary cannabinoids, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), elicit very different pharmacological effects. THC/CBD ratios are currently determined by techniques not readily accessible by consumers or dispensaries and which are impractical for use in the field by law-enforcement agencies. CuPc- and F16-CuPc-based organic thin-film transistors have been combined with a cannabinoid-sensitive chromophore for the detection and differentiation of THC and CBD. The combined use of these well-characterized and inexpensive p- and n-type materials afforded the determination of the CBD/THC ratio from rapid plant extracts, with results indistinguishable from high-pressure liquid chromatography. Analysis of the prepyrolyzed sample accurately predicted postpyrolysis THC/CBD, which ultimately influences the psychotropic and medicinal effects of the specific plant. The devices were also capable of vapor-phase sensing, producing a unique electrical output for THC and CBD relative to other potentially interfering vaporized organic products. The analysis of complex medicinal plant extracts and vapors, normally reserved for advanced analytical infrastructure, can be achieved with ease, at low cost, and on the spot, using organic thin-film transistors.

Metal and metalloid phthalocyanines are an abundant and established class of materials widely used in the dye and pigment industry as well as in commercial photoreceptors. Silicon phthalocyanines (SiPcs) are among the highest-performing n-type semiconductor materials in this family when used in organic thin-film transistors (OTFTs) as their performance and solid-state arrangement are often increased through axial substitution. Herein, we study eight axially substituted SiPcs and their integration into solution-processed n-type OTFTs. Electrical characterization of the OTFTs, combined with atomic force microscopy (AFM), determined that the length of the alkyl chain affects device performance and thin-film morphology. The effects of high-temperature annealing and spin coating time on film formation, two key processing steps for fabrication of OTFTs, were investigated by grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray diffraction (XRD) to elucidate the relationship between thin-film microstructure and device performance. Thermal annealing was shown to change both film crystallinity and SiPc molecular orientation relative to the substrate surface. Spin time affected film crystallinity, morphology, and interplanar d-spacing, thus ultimately modifying device performance. Of the eight materials studied, bis(tri-n-butylsilyl oxide) SiPc exhibited the greatest electron field-effect mobility (0.028 cm2 V-1 s-1, a threshold voltage of 17.6 V) of all reported solution-processed SiPc derivatives.