P and N type copper phthalocyanines as effective semiconductors in organic thin-film transistor based DNA biosensors at elevated temperatures

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

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.

The chemical and electrochemical stimuli viologen substituted phthalocyanine with tunable optical features1

In this study, viologen-tetrasubstituted Zn(II) phthalocyanines (PcV1 and PcV2) were designed and synthesized to achieve the tunable optical features via redox-active viologen groups. Several parameters relevant to the evaluation of the tunable optical features have been investigated: UV-Vis, cyclic voltammetry (CV), EPR, square wave voltammetry (SWV), and theoretical analyses. The results showed that upon reductions and oxidations of viologen groups either chemically or electrochemically, the optical features of PcV1 and PcV2 change drastically with switchable processes. These outcomes indicate that achieving control over optical features of large organic chromophores such as Pc with our rational design can be used for the design of new complex organic electronic materials.

Strong Magnetic Field Annealing for Improved Phthalocyanine Organic Thin-Film Transistors

Thin-film microstructure, morphology, and polymorphism can be controlled and optimized to improve the performance of carbon-based electronics. Thermal or solvent vapor annealing are common post-deposition processing techniques; however, it can be difficult to control or destructive to the active layer or substrates. Here, the use of a static, strong magnetic field (SMF) as a non-destructive process for the improvement of phthalocyanine (Pc) thin-film microstructure, increasing organic thin-film transistor (OTFTs) mobility by twofold, is demonstrated. Grazing incident wide-angle X-ray scattering (GIWAXS), X-ray diffraction (XRD), and atomic force microscopy (AFM) elucidate the effect of SMF on both para- and diamagnetic Pc thin-films when subjected to a magnetic field. A SMF is found to increase the concentration of oxygen-induced radical species within the Pc thin-film, lending a paramagnetic character to ordinarily diamagnetic metal-free Pc and resulting in magnetic field induced changes to its thin-film microstructures. In a nitrogen environment, without competing degradation effects of molecular oxygen, SMF processing is found to favorably improve charge transport characteristics and increase OTFT mobility. Thus, post-deposition thin-film annealing with a magnetic field is presented as an alternative and promising technique for future thin-film engineering applications.

Surface engineering of zinc phthalocyanine organic thin-film transistors results in part-per-billion sensitivity towards cannabinoid vapor

Phthalocyanine-based organic thin-film transistors (OTFTs) have been demonstrated as sensors for a range of analytes, including cannabinoids, in both liquid and gas phases. Detection of the primary cannabinoids, Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD), is necessary for quality control and regulation, however, current techniques are often not readily available for consumers, industry, and law-enforcement. The OTFT characteristics, X-ray diffraction (XRD) spectra, and grazing incident wide angle x-ray scattering (GIWAXS) spectra of two copper and three zinc phthalocyanines, with varying degrees of peripheral fluorination, were screened to determine sensitivity to THC vapor. Unsubstituted ZnPc was found to be the most sensitive material and, by tuning thin-film morphology, crystal polymorphs, and thickness through altered physical vapor deposition conditions, we increased the sensitivity to THC by 100x. Here we demonstrate that deposition conditions, and the resulting physical film characteristics, play a significant role in device sensitization.

Organic small molecule semiconductor materials for OFET-based biosensors

Biosensors is an advanced detection and monitoring device for the development of biotechnology, and is also a rapid and microanalytical device at the molecular level. Demands for high sensitivity, high flexibility, good biocompatibility, easy chemical modification and low cost offer incentive for exploring new materials to develop the next-generation biosensors. With the vigorous development of organic electronics, the performances of organic devices have been effectively improved, leading to organic semiconductor materials with low cost, good flexibility, easy chemical modification and good biocompatibility for biosensors. Biosensors based on organic field-effect transistors (OFETs) have become one of the most advanced biosensor platforms because of their inherent ability to amplify received signals. Furthermore, OFET-based biosensors have been widely used in the detection of DNA, protein, cell, glucose and other biological substances due to its high sensitivity, fast analysis speed, label-free detection, small size and simple operation. This mini review briefly discusses the organic small molecule semiconductor materials, device configurations, basic principles and application fields of OFETs-based biosensors.

The Need to Pair Molecular Monitoring Devices with Molecular Imaging to Personalize Health

By enabling the non-invasive monitoring and quantification of biomolecular processes, molecular imaging has dramatically improved our understanding of disease. In recent years, non-invasive access to the molecular drivers of health versus disease has emboldened the goal of precision health, which draws on concepts borrowed from process monitoring in engineering, wherein hundreds of sensors can be employed to develop a model which can be used to preventatively detect and diagnose problems. In translating this monitoring regime from inanimate machines to human beings, precision health posits that continual and on-the-spot monitoring are the next frontiers in molecular medicine. Early biomarker detection and clinical intervention improves individual outcomes and reduces the societal cost of treating chronic and late-stage diseases. However, in current clinical settings, methods of disease diagnoses and monitoring are typically intermittent, based on imprecise risk factors, or self-administered, making optimization of individual patient outcomes an ongoing challenge. Low-cost molecular monitoring devices capable of on-the-spot biomarker analysis at high frequencies, and even continuously, could alter this paradigm of therapy and disease prevention. When these devices are coupled with molecular imaging, they could work together to enable a complete picture of pathogenesis. To meet this need, an active area of research is the development of sensors capable of point-of-care diagnostic monitoring with an emphasis on clinical utility. However, a myriad of challenges must be met, foremost, an integration of the highly specialized molecular tools developed to understand and monitor the molecular causes of disease with clinically accessible techniques. Functioning on the principle of probe-analyte interactions yielding a transducible signal, probes enabling sensing and imaging significantly overlap in design considerations and targeting moieties, however differing in signal interpretation and readout. Integrating molecular sensors with molecular imaging can provide improved data on the personal biomarkers governing disease progression, furthering our understanding of pathogenesis, and providing a positive feedback loop toward identifying additional biomarkers and therapeutics. Coupling molecular imaging with molecular monitoring devices into the clinical paradigm is a key step toward achieving precision health.

Temperature Sensors Based on Organic Field-Effect Transistors

The rapid growth of wearable electronics, Internet of Things, smart packaging, and advanced healthcare technologies demand a large number of flexible, thin, lightweight, and ultralow-cost sensors. The accurate and precise determination of temperature in a narrow range (~0–50 °C) around ambient temperatures and near-body temperatures is critical for most of these applications. Temperature sensors based on organic field-effect transistors (OFETs) have the advantages of low manufacturing cost, excellent mechanical flexibility, easy integration with other devices, low cross-sensitivity, and multi-stimuli detectability and, therefore, are very suitable for the above applications. This article provides a timely overview of research progress in the development of OFET-based temperature sensors. First, the working mechanism of OFETs, the fundamental theories of charge transport in organic semiconductors, and common types of OFET temperature sensors based on the sensing element are briefly introduced. Next, notable advances in the development of OFET temperature sensors using small-molecule and polymer semiconductors are discussed separately. Finally, the progress of OFET temperature sensors is summarized, and the challenges associated with OFET temperature sensors and the perspectives of research directions in this field are presented.

The Rise of Silicon Phthalocyanine: From Organic Photovoltaics to Organic Thin Film Transistors

Silicon phthalocyanines are emerging n-type semiconductors for use in organic photovoltaics (OPVs) and organic thin-film transistors (OTFTs). Their low synthetic complexity paired with their versatile axial group facilitates the fine-tuning of their chemical properties, solution properties and processing characteristics without significantly affecting their frontier orbital levels or their absorption properties. The crystal engineering and film forming characteristics of silicon phthalocyanine semiconductors can be tuned through appropriate axial group functionalization, therefore facilitating their integration into both OTFTs and OPVs by solution processing or vapor deposition. This Spotlight on Applications will discuss recent advances in the integration of this exciting class of phthalocyanine into OTFTs and OPVs and highlights their promising future.

Metal phthalocyanines: thin-film formation, microstructure, and physical properties

Metal phthalocyanines (MPcs) are an abundant class of small molecules comprising of a highly conjugated cyclic structure with a central chelated metal ion. Due to their remarkable chemical, mechanical, and thermal stability MPcs have become popular for a multitude of applications since their discovery in 1907. The potential for peripheral and axial functionalization affords structural tailoring to create bespoke MPc complexes for various next generation applications. Specifically, thin-films of MPcs have found promising utility in medical and electronic applications where the need to understand the relationship between chemical structure and the resulting thin-film properties is an important ongoing field. This review aims to compile the fundamental principles of small molecule thin-film formation by physical vapour deposition and solution processing focusing on the nucleation and growth of crystallites, thermodynamic and kinetic considerations, and effects of deposition parameters on MPc thin-films. Additionally, the structure-property relationship of MPc thin-films is examined by film microstructure, morphology and physical properties. The topics discussed in this work will elucidate the foundations of MPc thin-films and emphasize the critical need for not only molecular design of new MPcs but the role of their processing in the formation of thin-films and how this ultimately governs the performance of the resulting application.

A "concentration-induced self-assembly" strategy for Ag x H3-x PMo12O40 nanorods: synthesis, photoelectric properties and photocatalytic applications

Polyoxometalates (POMs) as molecule-based metal oxides have exhibited significant application in catalysis and materials science, but the synthesis of pristine POM nanomaterials still remains a challenge. In this work, we find a novel strategy of concentration-induced self-assembly for gaining pristine POM nanorods Ag _x H_3-x PMo₁₂O₄₀ (denoted as AgHPMo₁₂), which are synthesized only from both POMs and silver ion Ag⁺ in an aqueous solution at room temperature. The controllable concentrations of the cationic and anionic components in the aqueous solution become the critical factor for the successful synthesis. In addition, the photoelectric properties of AgHPMo₁₂ nanorods were investigated as compared to those of AgHPMo₁₂ particles, indicating a superior photoelectric performance of AgHPMo₁₂ nanorods to AgHPMo₁₂ particles. Furthermore, AgHPMo₁₂ nanorods/phthalocyanine heterojunction photocatalysts were prepared for evaluating photocatalytic degradation of tetracycline hydrochloride, showing an efficient photocatalytic performance due to the advantages of the nanorods and type II heterostructure.

Thin-Film Engineering of Solution-Processable n-Type Silicon Phthalocyanines for 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.

Silicon phthalocyanines: synthesis and resurgent applications

Their unique axial bonds and NIR optical properties have made silicon phthalocyanines (SiPcs) valuable compounds. Herein, we present key synthetic strategies and emerging applications of SiPcs over the past decade.

Engineering Cannabinoid Sensors through Solution-Based Screening of Phthalocyanines

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.

Controlled Synthesis of Poly(pentafluorostyrene-ran-methyl methacrylate) Copolymers by Nitroxide Mediated Polymerization and Their Use as Dielectric Layers in Organic Thin-film Transistors

A library of statistically random pentafluorostyrene (PFS) and methyl methacrylate (MMA) copolymers with narrow molecular weight distributions was produced, using nitroxide mediated polymerization (NMP) to study the effect of polymer composition on the performance of bottom-gate top-contact organic thin-film transistors, when utilized as the dielectric medium. Contact angle measurements confirmed the ability to tune the surface properties of copolymer thin films through variation of its PFS/MMA composition, while impedance spectroscopy determined the effect of this variation on dielectric properties. Bottom-gate, top-contact copper phthalocyanine (CuPc) based organic thin-film transistors were fabricated using the random copolymers as a dielectric layer. We found that increasing the PFS content led to increased field-effect mobility, until a point after which the CuPc no longer adhered to the polymer dielectric.

Developing and Comparing 2,6-Anthracene Derivatives: Optical, Electrochemical, Thermal, and Their Use in Organic Thin Film Transistors

Anthracene-based semiconductors have attracted great interest due to their molecular planarity, ambient and thermal stability, tunable frontier molecular orbitals and strong intermolecular interactions that can lead to good device field-effect transistor performance. In this study, we report the synthesis of six anthracene derivatives which were di-substituted at the 2,6-positions, their optical, electrochemical and thermal properties, and their single crystal structures. It was found that 2,6-functionalization with various fluorinated phenyl derivatives led to negligible changes in the optical behaviour while influencing the electrochemical properties. Furthermore, the choice of fluorinated phenyl moiety had noticeable effects on melting point and thermal stability (ΔTm < 55 °C and ΔTd < 65 °C). Bottom-gate top-contact (BGTC) organic thin transistors (OTFTs) were fabricated and characterized using the 2,6-anthracene derivatives as the semiconducting layer. The addition of fluorine groups on the phenyl groups led to a transition from p-type behaviour to n-type behaviour in BGBC OTFTs.

Air and temperature sensitivity of n-type polymer materials to meet and exceed the standard of N2200

N-type organic semiconductors are notoriously unstable in air, requiring the design of new materials that focuses on lowering their LUMO energy levels and enhancing their air stability in organic electronic devices such as organic thin-film transistors (OTFTs). Since the discovery of the notably air stable and high electron mobility polymer poly{[N,N'-bis (2-octyldodecyl)- naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,29-bisthiophene)} (N2200), it has become a popular n-type semiconductor, with numerous materials being designed to mimic its structure. Although N2200 itself is well-studied, many of these comparable materials have not been sufficiently characterized to compare their air stability to N2200. To further the development of air stable and high mobility n-type organic semiconductors, N2200 was studied in organic thin film transistors alongside three N2200-based analogues as well as a recently developed polymer based on a (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b']difuran-2,6(3 H,7 H)-dione (IBDF) core. This IBDF polymer has demonstrated promising field-effect mobility and air stability in drop-cast OTFTs. While N2200 outperformed its analogues, the IBDF-based polymer displayed superior air and temperature stability compared to N2200. Overall, polymers with more heteroatoms displayed greater air stability. These findings will support the development of new air-stable materials, and further demonstrate the persistent need for the development of novel n-type semiconductors.

On-the-Spot Detection and Speciation of Cannabinoids Using Organic Thin-Film Transistors

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.

Developing 9,10-anthracene Derivatives: Optical, Electrochemical, Thermal, and Electrical Characterization

Anthracene-based semiconductors are a class of molecules that have attracted interest due to their air stability, planarity, potential for strong intermolecular interactions, and favorable frontier molecular orbital energy levels. In this study seven novel 9,10-anthracene-based molecules were synthesized and their optical, electrochemical, and thermal properties were characterized, along with their single crystal arrangement. We found that functionalization of the 9,10-positions with different phenyl derivatives resulted in negligible variation in the optical properties with minor (±0.10 eV) changes in electrochemical behavior, while the choice of phenyl derivative greatly affected the thermal stability (Td > 258 °C). Preliminary organic thin film transistors (OTFTs) were fabricated and characterized using the 9,10-anthracene-based molecules as the semiconductor layer. These findings suggest that functionalization of the 9,10-position of anthracene leads to an effective handle for tuning of the thermal stability, while having little to no effect on the optical properties and the solid-state arrangement.

Silicon Phthalocyanines as Acceptor Candidates in Mixed Solution/Evaporation Processed Planar Heterojunction Organic Photovoltaic Devices

Silicon phthalocyanines (SiPc) are showing promise as both ternary additives and non-fullerene acceptors in organic photovoltaics (OPVs) as a result of their ease of synthesis, chemical stability and strong absorption. In this study, bis(3,4,5-trifluorophenoxy) silicon phthalocyanine ((345F)2-SiPc)) and bis(2,4,6-trifluorophenoxy) silicon phthalocyanine ((246F)2-SiPc)) are employed as acceptors in mixed solution/evaporation planar heterojunction (PHJ) devices. The donor layer, either poly(3-hexylthiophene) (P3HT) or poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), was spin coated followed by the evaporation of the SiPc acceptor thin film. Several different donor/acceptor combinations were investigated in addition to investigations to determine the effect of film thickness on device performance. Finally, the effects of annealing, prior to SiPc deposition, after SiPc deposition, and during SiPc deposition were also investigated. The devices which performed the best were obtained using PCDTBT as the donor, with a 90 nm film of (345F)2-SiPc as the acceptor, followed by thermal annealing at 150 °C for 30 min of the entire mixed solution/evaporation device. An open-circuit voltage (Voc) of 0.88 V and a fill factor (FF) of 0.52 were achieved leading to devices that outperformed corresponding fullerene-based PHJ devices.

Metal phthalocyanine organic thin-film transistors: changes in electrical performance and stability in response to temperature and environment

Metal phthalocyanines (MPcs) are a widely studied class of materials that are frequently used in organic thin-film transistors (OTFTs), organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs). The stability of these devices and the materials used in their fabrication is important to realize their widespread adoption. Seven P-type MPcs: zinc (ZnPc), magnesium (MgPc), aluminum (AlClPc), iron (FePc), cobalt (CoPc), and titanium (TiOPc) were investigated as the semiconductors in OTFTs under varying temperatures (25 °C to 150 °C) and environmental conditions (air and vacuum, P < 0.1 Pa). Devices using the divalent MPcs (except MgPc) showed significant shifts in threshold voltage and field-effect mobility with rising temperature in both air and vacuum. AlClPc and TiOPc, on the other hand, had more stable electrical properties, making them useful for applications requiring consistent performance. Distinct variations in film morphology as determined by atomic force microscopy may explain the different thermal response between the two groups of MPcs, while thermal gravimetric analysis in air and nitrogen (N₂) provides additional insight into their susceptibility to oxidation at elevated temperature. To demonstrate proof-of-concept thermal sensing under realistic operating conditions, current changes were monitored in response to temperature stimuli using two more sensitive divalent MPcs. This comparative study of the effect of central atom inclusion in MPcs, the resulting material stability and thin-film characteristics will facilitate design of future sensors and other OTFT applications.

A series of metal phthalocyanine based organic thin film transistors were evaluated and their responses to changes in temperature and environmental was determined: the choice of central atom makes a difference.