(F5PhO)2-F16-SiPc as an air-stable, high-performance n-type semiconductor with poor cannabinoid sensing capabilities

Abstract

Organic thin-film transistors (OTFTs) are an emerging platform for rapid, point-of-source detection and speciation of Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD). (F₅PhO)₂-F₁₆-SiPc semiconductor was implemented into high performance, air-stable n-type bottom gate, bottom contact OTFTs, however, the resulting device performance changes in response to THC and CBD were negligible. We explored the orientation of the corresponding thin films by synchrotron-based grazing incidence wide-angle X-ray scattering (GIWAXS) and angle-dependent near-edge X-ray absorption fine structure (NEXAFS), as well as polarized Raman microscopy. These techniques demonstrate for the first time that (F₅PhO)₂-F₁₆-SiPc molecules are at a 45–48° orientation to the substrate; comparable to other reported R₂-SiPcs. This orientation did not change upon exposure to THC and CBD, which has previously been reported for phthalocyanine-based OTFT cannabinoid sensors. The presence of two bulky axial groups, along with the absence of hydrogens in the molecule and the low reactivity of the silicon atom likely causes the lack of interaction with the cannabinoids. While (F₅PhO)₂-F₁₆-SiPc may be a successfully air-stable n-type semiconductor for OTFTs, the structural changes performed to make it air stable over traditional non-fluorinated silicon MPcs, are likely responsible for its lack of response to cannabinoid exposure.