1. Nitroxide Medaited Polymerization (NMP)
Promising candidates for next generation sensors, drug delivery vehicles or chemical logic gate operators are smart polymers. These smart polymers undergo a significant physical change when exposed to small changes in the local environment. This environmental stimulus can be anything from temperature, electrical potential, pH or even light. Good molecular control of the polymers is essential to tune the responsiveness or to incorporate multiple, different stimuli-responses. Over the last 15-20 years the interest in reversible-deactivation radical polymerization (RDRP) more commonly known as controlled radical polymerization (CRP) has vastly expanded due to its ability to produce highly defined polymers on a molecular level, which rival those produced by traditional, and more stringent, living techniques such as ionic polymerization. Nitroxide-mediated polymerization (NMP), a type of CRP, has realistic scale-up potential and can be used to produce highly defined smart polymers without the need of air-free transfers, transition metal catalysts or problematic thiol agents. Therefore, no additional purification of the final polymer is necessary prior to being used for sensitive electronic or biological applications. My research focuses on using NMP for the synthesis of model functional materials with controlled microstructure for numerous applications such as organic electronic applications.
Recent publications on this topic:
King, B.; Lessard, B. H.* Controlled Synthesis and Degradation of Poly(N-(Isobutoxymethyl) Acrylamide) Homopolymers and Block Copolymers. Macromol. React. Eng. 2017 11, 2, 1600073 (1-10). (Advanced Science News, Cover Article) doi: 10.1002/mren.201600073
Melville, O.; Imperiale, C.; King, B.; Lessard, B. H.* Orthogonally Processable Carbazole-Based Polymer Thin Films by Nitroxide-Mediated Polymerization. Langmuir bf 2016, 32, 13640-13648. doi:10.1021/acs.langmuir.6b0392
Kannan, N. B. and Lessard, B. H.* Copolymerization of 2,3,4,5,6-Pentafluorostyrene and Methacrylic Acid by Nitroxide-Mediated Polymerization: The Importance of Reactivity Ratios. Macromol. Reaction Eng., 2016, 10, 600-610. (Cover article) doi:10.1002/mren.201600052
2. Dye Chemistry
Organic electronics utilize carbon based semiconductors in place of the conventional inorganic semiconductor. The same characteristics which make dyes and pigments colourful and photo luminescent also make them desirable as organic semiconductors. Therefore the use of commercial dyes and pigments as starting materials is ideal due to their wide availability and low manufacturing cost. Unfortunately the majority of these molecules do not possess necessary photo physical and solid state characteristics. Through organic chemistry we can tune the molecule solubility, its solid state arrangement and its photo physical properties, therefore, improving their performance in organic electronic devices. Phthalocyanines, for example, are commercial dyes used as a pigment, colourant and even xerographic material. We have several ongoing projects which utilize silicon phthalocyanines as active materials in organic photovoltaics.
Recent publications on this topic:
Grant, T. M.; Melville, O. A.; Lessard, B. H.* Silicon Phthalocyanines as N-Type Semiconductors in Organic Thin Film Transistors. J. Mater. Chem. C, 2018, 6,5482-5488. doi: 10.1039/C8TC01116H
Grant, T. M.; Dang, Ming T.; Han, Y.; Seferos, D.; Lessard, B. H.*; Bender, T. P.* Bis(tri-n-alkylsilyl oxide) silicon phthalocyanines: A Start to Establishing a Structure Property Relationship as both Ternary Additives and Non-Fullerene Electron Acceptors in Bulk Heterojunction Organic Photovoltaic Devices. J. Mater. Chem. A, 2017, 5, 12168-12182. doi: 10.1039/C6TA10739G