Mark Giles

High ambipolar and balanced carrier mobility in regioregular poly(3-hexylthiophene)

The carrier transport of carefully purified regioregular poly(3-hexylthiophene) films has been studied using time-of-flight photocurrent measurements. We find balanced ambipolar transport with a room-temperature mobility for holes of 3×10−4cm2V−1s−1 and for electrons of 1.5×10−4cm2V−1s−1 at electric fields ⩾105V∕cm. The transport is relatively field independent and weakly temperature dependent, pointing to a high degree of chemical regioregularity and purity. These factors make poly(3-hexylthiophene) attractive for use in a range of electronic applications.

Polymerisable liquid crystalline organic semiconductors and their fabrication in organic field effect transistors

The performance of the semiconducting component in organic field effect transistors (OFETs) is a key parameter in the advancement of organic electronic devices. New semiconductors are required, which can be solution processed, possess high mobility and current modulation, and are stable in ambient conditions. This work provides the first demonstration of working field effect transistor devices fabricated from novel solution processible, polymerisable, small molecule liquid crystalline semiconductors, referred to as reactive mesogens. The design, synthesis, and performance of these materials in transistor devices are reported. The relationship between liquid crystal molecular structure, its corresponding phase behaviour and electrical performance is examined. Molecular design methodology was employed to control the liquid crystalline morphology, in an attempt to optimise organisation and packing. Alignment of the molecules in large homeotropic domains was achieved through surface treatment techniques, and the highly ordered mesophase was preserved by polymerisation of the reactive end groups, creating a crosslinked network.

Further evidence for spontaneous solid-state polymerisation reactions in 2,5-dibromothiophene derivatives

Three new, highly crystalline 2,5-dibromothiophene compounds polymerise on standing in the absence of solvent and catalyst; X-ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, facilitating the coupling of monomers.

Amplified fluorescence quenching in high ionic strength media

We report a new cationic poly(phenylene ethynylene) (PPE) derivative that exhibits strong amplified fluorescence quenching in the presence of electron-deficient species, yielding high Stern-Volmer coefficients of 4.7 × 10 M in aqueous solutions. Importantly, with the addition of appropriate non-ionic surfactants, the polymer is found to retain its excellent sensitivity even when transferred to high ionic strength buffered media, which have previously been shown to suppress the amplified quenching effect in other polyelectrolyte systems. The cationic PPE derivative yields Stern-Volmer coefficients as high as 10 M in 25 mM buffer solutions of both tris(hydroxymethyl) aminomethane (Tris) and sodium acetate containing 150 mM sodium chloride, the optimal conditions for many enzymes such as phosphatases. The ability to maintain high Stern-Volmer coefficients in high ionic strength buffered media extends the applicability of ionic conjugated polymers to high sensitivity detection in biological media, and thus greatly enhances their versatility as biological sensors.

Efficient quenching of a guanidinium-containing fluorescence sensor.

Conjugated polymers (CPs) have attracted considerable interest owing to their applications in optoelectronic devices such as light-emitting diodes (LEDs), solar cells, and thin-film transistors (TFTs). In recent years there has been increasing interest in exploiting CPs as chemical and biological sensors due to the strong fluorescence quenching they exhibit in the presence of electron deficient species, and their consequent ability to detect trace levels of biological analytes at mM concentrations and below. 8, 9] The efficiency of the quenching process can be quantified by the Stern–Volmer equation [Eq. (1)] which relates the emission intensity I to the quencher concentration [Q]:

Stable semiconducting thiophene polymers and their field effect transistor characteristics

The development of p-type semiconducting polymers demonstrating good stability under ambient operation is of importance for the development of low cost, printed electronics. We present here the synthesis and full characterisation of two soluble terthiophene polymers, and examine the effect of introducing a fused aromatic heterocycle, thieno[2,3-b]thiophene, into a terthiophene polymer backbone. This heterocycle contains a cross-conjugated central double bond, and its inclusion was shown to have a marked influence on the optical, thermal and electrical properties of the terthiophene polymer. Transistors were fabricated from both polymers, and the operation and storage lifetime under ambient operation was compared.

Self-assembled liquid crystalline solution processable semiconductors

This work describes the development of solution processable liquid crystalline semiconductors and their applications in field-effect transistors. The relationship between liquid crystal molecular structure, its corresponding phase behaviour and electrical performance is examined. Molecular design methodology is employed to control the liquid crystalline morphology. The thermal, optical and electrical behaviour of these materials is characterised and X-ray diffraction scattering technique is used to reveal details of morphology and molecular orientation.

Reliable Suzuki Chemistry For Functionalised Polythiophene Synthesis

Until recently, the synthesis of polythiophenes using Suzuki chemistry has proven difficult because of the ready protodeborylation of thiophene boronates. However, we now report that the new generation of bulky, electron-rich Pd(0)-phosphane catalysts are effective and reliable for the preparation of regioregular polyalkylthiophenes using Suzuki coupling. Moreover, the monomers can be prepared in high yield by Ir-catalysed borylation, without the need for strong organolithium bases, making this potentially a highly functional group-tolerant approach to polyalkylthiophene derivatives. Perfluoroalkylthiophenes also undergo this reaction.

New Liquid Crystalline Semiconductors And Their Fabrication in Organic Field Effect Transistor Devices

The performance of the semiconducting component in organic field effect transistors (OFETs), is a key parameter in the advancement of organic electronic devices. This work describes the development of solution processible liquid crystalline semiconductors, both main chain rigid rod polymers and small molecule polymerisable liquid crystals, referred to as reactive mesogens. New conjugated main chain polymeric semiconductors have been designed, synthesised, and their performance in transistor devices is reported. Small molecule liquid crystalline semiconductors, which contain reactive end groups, were also prepared, and their design, characterisation, and performance in transistor devices is discussed.