Paul Baek

Highly functionalisable polythiophene phenylenes

The synthesis and properties of novel conducting polymer monomers, and their polymers, based on poly(thiophene phenylenes) (PThP) is described. These polymers contain a range of functional groups useful for further polymer modification and design and can be obtained using both electropolymerisation and chemical oxidative polymerisation. Further modification of a chemically polymerised PThP was validated using ‘click’ chemistry from azide containing side chains and also by grafting of polystyrene by Activator ReGenerated by Electron Transfer Atom Transfer Radical polymerisation (ARGET-ATRP) from ATRP initiating sites on the polymer. The complimentary and orthogonal nature of ‘click’ chemistry and ATRP grafting was established. The polymers were characterised by 1H NMR, UV-Vis spectroscopy and cyclic voltammetry. Electrochemical analysis showed that the functionalised polymers retain excellent electroactivity.

New immobilisation method for oligonucleotides on electrodes enables highly-sensitive, electrochemical label-free gene sensing

We present a versatile and facile procedure for the immobilisation of bioprobe molecules to an electrochemical sensing element. We eliminate lengthy preparation procedures for direct functionalisation of electrode surfaces by pre-attaching probe molecules to carboxylic acid bearing termonomers of pyrrole phenylenes or thiophene phenylenes. We demonstrate that these conjugates can be electrodeposited at low potentials to form nano-scale porous, electroactive conducting polymer films, exposing the bioprobe and retaining activity and specificity for binding, exemplified here with DNA sensors. The electrochemical reaction impedance for Fe(CN)63-/4- on oligonucleotide-modified electrodes showed remarkable (down to aM) detection sensitivity for target DNA sequences present in solution. Cross-sensitivity to non-complementary target sequences is small and multi-target arrays are easily made. There is no need for labelling of either probe or target oligonucleotide.

Thermoresponsive laterally-branched polythiophene phenylene derivative as water-soluble temperature sensor

Polymers with thermoresponsive properties have received a strong interest due to their potential applications. Here we report the synthesis and characterisation of a water soluble and thermoresponsive polythiophene derivative. Firstly, a polythiophene phenylene (PThP) functionalised with an initiator for atom transfer radical polymerization (ATRP) and azide groups on the side chains was synthesised. Secondly, ATRP was employed to graft poly(ethylene glycol) methacrylate (PEGMA) from the PThP to create a permanently water soluble conjugated polymer. Further functionalisation was then conducted through the ‘click’ reaction with propargyl functionalised poly(2-n-propyl-2-oxazoline) to introduce thermoresponsivness. The polymer displayed lower critical solution temperature (LCST) behavior, as revealed by fluorescence and UV-Vis spectroscopy with potential use as soluble polymeric thermometer.

Polymer electronic composites that heal by solvent vapour

Recent advances in organic electronic devices have reached new milestones in performance and function, and they are used in applications ranging from displays to sensory devices. However, they still present limitations in mechanical flexibility and electrical durability following the damage caused during their lifetime. Herein, we present a simple route to prepare conducting polymer composites that can address some of these issues through solvent vapour-induced healing of cracks formed within conducting polymer composites. Conducting polymer composites were prepared by solution blending of poly(3-hexylthiophene) (P3HT) and poly(dimethylsiloxane) (PDMS)-containing urea segmented copolymer. The bicomponent composites with various weight fractions of neutral P3HT were used to demonstrate their electroactivity whereas the electrical conductivity, mechanical and solvent vapour-induced self-healing studies were carried out with composites with various weight fractions of FeCl3-doped P3HT. A mechanically bisected free-standing film with 30 wt% of doped P3HT was observed to be readily healed through exposure to solvent vapour at room temperature, with a mechanical healing efficiency of 55 ± 24% and restoration of electrical conductivity up to 82 ± 1%.

Molecular Approach to Conjugated Polymers with Biomimetic Properties

The field of bioelectronics involves the fascinating interplay between biology and human-made electronics. Applications such as tissue engineering, biosensing, drug delivery, and wearable electronics require biomimetic materials that can translate the physiological and chemical processes of biological systems, such as organs, tissues. and cells, into electrical signals and vice versa. However, the difference in the physical nature of soft biological elements and rigid electronic materials calls for new conductive or electroactive materials with added biomimetic properties that can bridge the gap. Soft electronics that utilize organic materials, such as conjugated polymers, can bring many important features to bioelectronics. Among the many advantages of conjugated polymers, the ability to modulate the biocompatibility, solubility, functionality, and mechanical properties through side chain engineering can alleviate the issues of mechanical mismatch and provide better interface between the electronics and biological elements. Additionally, conjugated polymers, being both ionically and electrically conductive through reversible doping processes provide means for direct sensing and stimulation of biological processes in cells, tissues, and organs. In this Account, we focus on our recent progress in molecular engineering of conjugated polymers with tunable biomimetic properties, such as biocompatibility, responsiveness, stretchability, self-healing, and adhesion. Our approach is general and versatile, which is based on functionalization of conjugated polymers with long side chains, commonly polymeric or biomolecules. Applications for such materials are wide-ranging, where we have demonstrated conductive, stimuli-responsive antifouling, and cell adhesive biointerfaces that can respond to external stimuli such as temperature, salt concentration, and redox reactions, the processes that in turn modify and reversibly switch the surface properties. Furthermore, utilizing the advantageous chemical, physical, mechanical and functional properties of the grafts, we progressed into grafting of the long side chains onto conjugated polymers in solution, with the vision of synthesizing solution-processable conjugated graft copolymers with biomimetic functionalities. Examples of the developed materials to date include rubbery and adhesive photoluminescent plastics, biomolecule-functionalized electrospun biosensors, thermally and dually responsive photoluminescent conjugated polymers, and tunable self-healing, adhesive, and stretchable strain sensors, advanced functional biocidal polymers, and filtration membranes. As outlined in these examples, the applications of these biomimetic, conjugated polymers are still in the development stage toward truly printable, organic bioelectronic devices. However, in this Account, we advocate that molecular engineering of conjugated polymers is an attractive approach to a versatile class of organic electronics with both ionic and electrical conductivity as well as mechanical properties required for next-generation bioelectronics.