Francesco Marinelli

A sensitivity-enhanced field-effect chiral sensor

Organic thin-film transistor sensors have been recently attracting the attention of the plastic electronics community for their potential exploitation in novel sensing platforms. Specificity and sensitivity are however still open issues: in this respect chiral discrimination-being a scientific and technological achievement in itself--is indeed one of the most challenging sensor bench-tests. So far, conducting-polymer solid-state chiral detection has been carried out at part-per-thousand concentration levels. Here, a novel chiral bilayer organic thin-film transistor gas sensor--comprising an outermost layer with built-in enantioselective properties-is demonstrated to show field-effect amplified sensitivity that enables differential detection of optical isomers in the tens-of-parts-per-million concentration range. The ad-hoc-designed organic semiconductor endowed with chiral side groups, the bilayer structure and the thin-film transistor transducer provide a significant step forward in the development of a high-performance and versatile sensing platform compatible with flexible organic electronic technologies.

9,10-Ter-anthrylene-ethynylene: a new molecular architecture for solution processed anthracene-based thin film transistors

This study deals with the properties of a new molecular architecture for organic thin film transistors obtained by introducing 10-decylanthr-9-yl-ethynyl moieties at the anthracene 9,10 positions. The resulting structure, formally a ter-anthrylene-ethynylene (D3ANT), is stable and endowed with sufficient solubility to guarantee the formation of good quality films. The molecule was characterised by 1H NMR, mass spectrometry, IR, UV–vis and photoluminescence both in solution and in the solid state. Cyclic voltammetry measurements, combined with solution UV–vis, permitted the evaluation of HOMO and LUMO energy levels. A series of D3ANT-based OTFT devices were built both in bottom and top contact configurations by a spin coating technique. Top contact OTFT devices exhibited the best semiconducting characteristics, showing an average mobility of 1.2 × 10−2 cm2 V−1 s−1 with on–off ratios higher then 104, while the highest mobility obtained was 0.055 cm2 V−1 s−1. AFM thin-film characterization showed evidence of a granular structure. High-resolution STM images of D3ANT monolayers adsorbed on Au(111) and HOPG reveal highly-ordered self-organized domains with molecules lying flat on the substrates, but, remarkably, no reflections were recorded by out-of plane GIXRD of spin coated films on SiO2.

Solution processable ter-anthrylene-ethynylenes semiconductors: thin film transistor properties and STM study on HOPG and Au(111)

The article reports the properties of new solution processable 9,10-ter-anthrylene-ethynylenes functionalised with n-butyl (B3A) n-octyl (O3A) and 2-ethyl-hexyl (E3A) functional groups. The characterization of the oligomers as organic semiconductors in solution processed top-contact bottom-gate OTFT devices reveal that E3A shows the best figures of merit (average μ of 1.1 ± 0.1 × 10−2 cm2 V−1 s−1 and on/off ratios of 105). Spontaneous physisorption of all the molecules on both highly ordered pyrolytic graphite (HOPG) and reconstructed Au(111) surfaces allowed the study of their self assembling behaviour at the liquid–solid interface by scanning tunnelling microscopy. STM revealed a peculiar behaviour for B3A, bearing shorter n-butyl chains, that arranges in a quasi hexagonal packing on HOPG, differently from the other molecules showing the formation of lamellae rows on this substrate. Due to the stronger interactions with the ter-anthrylene-ethynylene cores, on Au(111) surfaces, all structures self assemble in closer lamellar rows with very similar geometric parameters, independently from the alkyl chain length that are assumed to be tilted off the surface.

Solution processed ter-anthrylene-ethynylenes for annealing-activated organic field-effect transistors: a structure–performance correlation study

OFETs based on new solution-processed ester functionalized 9,10-ter-anthrylene-ethynylenes show a mobility increase of four orders of magnitude, leading to mobilities as high as 4.9 × 10−2 cm2 V−1s−1 if the deposited film is annealed before contact deposition. The behavior is ascribed to an increase in film order at the dielectric/semiconductor interface as revealed by X-ray studies.

A poly(phenyleneethynylene) polymer bearing amino acid substituents as active layer in enantioselective solid-state sensors

A poly(phenyleneethynylene) polymer bearing amino acid pendant groups is used as enantioselective active layer in solid-state sensing devices. The chiral analyte in the present study is menthol in both the natural (-) and synthetic (+) enantiomers. The polymer bearing amino acid chiral sites is demonstrated to interact more favorably with the natural menthol than the synthetic one in a quartz crystal microbalance revealing system. Promising perspectives are seen for the use of such polymers in chiral discriminating, chemically sensitive resistors or even transistors.

Organic Thin-Film Transistors with Enhanced Sensing Capabilities

Organic thin-film transistors, used as sensing devices, have been attracting quite a considerable interest lately as they offer advantages such as multi parameter behaviour and possibility to be quite easily molecularly tuned for the detection of specific analytes. Here, a study on the dependences of the devices responses on important parameters such as the active layer thickness and its morphology as well as on the transistor channel length is presented. To introduce the least number of variables the system chosen for this study is quite a simple and well assessed one being based on a thiophene oligomer active layer exposed to 1-butanol vapours.

Oligothiophenes bearing polar groups for organic thin film transistors: synthesis, characterisation and preliminary gas sensing results

The properties of a series of sexithiophenes bearing amide or ester functionalities in the alpha,omega-positions are reported. Isolation of the ester functionalities from the sexithiophene core by an ethylene spacer led to a device with moderate hole mobilities (1.2-10-2 cm2V-1s-1) and on/off ratios (103). A bottom contact device based on this sexithiophene showed a good response to a 5 ppm NO atmosphere, encouraging future studies on gas sensing OTFT based on these polar-functionalised OTFT.

Organic thin film transistors as plastic chiral sensors

Organic thin-film transistor (OTFT) sensors have been recently attracting the attention for their potential exploitation as novel sensors. Specificity and sensitivity are still open issues. Chiral discrimination is both a scientific and technological achievement in itself and, indeed, one of the most challenging sensorpsilas bench-test. In the present work, a chiral bilayer OTFT gas sensor - comprising an outermost layer with built in enantioselective properties - is demonstrated to exhibit field-effect amplified sensitivity that allows differential detection of optical isomers in the tens part-per-million (ppm) concentration range. The ad hoc designed organic semiconductor, endowed with chiral side groups, the bilayer structure and the TFT transducer, provide a significant step further in the development of a performing and versatile sensing platform compatible with flexible organic electronic technologies.