Axial Phenoxylation of Aluminum Phthalocyanines for Improved Cannabinoid Sensitivity in OTFT Sensors

Abstract

Cannabis producers, consumers, and regulators need fast, accurate, point‐of‐use sensors to detect Δ9‐tetrahydrocannabinol (THC) and cannabidiol (CBD) from both liquid and vapor source samples, and phthalocyanine‐based organic thin‐film transistors (OTFTs) provide a cost‐effective solution. Chloro aluminum phthalocyanine (Cl‐AlPc) has emerged as a promising material due to its unique coordinating interactions with cannabinoids, allowing for superior sensitivity. This work explores the molecular engineering of AlPc to tune and enhance these interactions, where a series of novel phenxoylated R‐AlPcs are synthesized and integrated into OTFTs, which are then exposed to THC and CBD solution and vapor samples. While the R‐AlPc substituted molecules have a comparable baseline device performance to Cl‐AlPc, their new crystal structures and weakened intermolecular interactions increase sensitivity to THC. Grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) and atomic force microscopy (AFM) are used to investigate this film restructuring, where a significant shift in the crystal structure, grain size, and film roughness is detected for the R‐AlPc molecules that do not occur with Cl‐AlPc. This significant crystal reorganization and film restructuring are the driving force behind the improved sensitivity to cannabinoids relative to Cl‐AlPc and demonstrate that analyte–semiconductor interactions can be enhanced through chemical modification to create more responsive OTFT sensors.

Organic Thin Film Transistor-Based Cannabinoid Sensors

“…In all cases, the phenoxy-AlPcs led to a reduction in OTFT performance, but an improvement in sensing response. AFM, XRD, UV–vis, and GIWAXS all demonstrated that the phenoxy-AlPcs exhibited greater changes in molecular structure and in some cases the appearance of new polymorphs were observed upon exposure to THC and CBD . We surmised that the phenoxy groups lead to additional possible interactions between the semiconductor and the THC and CBD, and a reduction in intermolecular AlPc interactions, leading to more significant changes in morphology, upon exposure, as observed.…”

“…AFM, XRD, UV−vis, and GIWAXS all demonstrated that the phenoxy-AlPcs exhibited greater changes in molecular structure and in some cases the appearance of new polymorphs were observed upon exposure to THC and CBD. 49 We surmised that the phenoxy groups lead to additional possible interactions between the semiconductor and the THC and CBD, and a reduction in intermolecular AlPc interactions, leading to more significant changes in morphology, upon exposure, as observed. This study demonstrated that simple modifications of the MPc semiconductor can be an effective way to improve OTFT sensors sensitivity.…”

“…Therefore, we synthesized a series of phenoxylated Cl-AlPcs (phenoxy-AlPc) and compared them with the baseline Cl-AlPc. 49 In all cases, the phenoxy-AlPcs led to a reduction in OTFT performance, but an improvement in sensing response. AFM, XRD, UV−vis, and GIWAXS all demonstrated that the phenoxy-AlPcs exhibited greater changes in molecular structure and in some cases the appearance of new polymorphs were observed upon exposure to THC and CBD.…”

“…Our group has employed this strategy to improve silicon phthalocyanine (R 2 -SiPc)-based OTFTs ,− and ammonia sensors , with great success. Therefore, we synthesized a series of phenoxylated Cl-AlPcs (phenoxy-AlPc) and compared them with the baseline Cl-AlPc . In all cases, the phenoxy-AlPcs led to a reduction in OTFT performance, but an improvement in sensing response.…”

Microfluidic-organic thin film transistor coupled platform for simple solution exposure

“…22 The use of organic semiconductors can also introduce unique interactions and sensing mechanisms to analytes such as the specific film restructuring of phthalocyanines with exposure to cannabinoids. [23][24][25][26][27] To date, the majority of reported OTFT sensors rely on manual deposition of analyte solutions, typically using micropipettes. 28,29 Though manual droplet dispensing can be convenient for single devices, it is not a scalable process for high-throughput testing, prevents continuous analysis, and has been shown to introduce significant run-to-run variation, limiting reproducibility.…”