24.3.2023 Radical-Ion Salts based on Thiazyls and Tetracyanoquinodimethane: Hysteretic Magnetic Bistability in a Multicomponent System (Taponen)

Organic radicals are subvalent molecules with one or more unpaired electrons. Typically, such species are reactive intermediates that are short-lived unless they are stabilized by steric protection, electronic delocalization, or a combination of both. Organothiazyls and their heavier selenazyl analogues are a broad class of stable radicals containing NS or NSe units combined with carbon.
FM Anni Taponen
Published
24.3.2023

In recent decades, they have become important building blocks for synthesizing advanced materials with fascinating and useful solid-state properties, such as conductivity, magnetism, and bistability. The first part of this thesis introduces some common stable radicals and the factors affecting their stability and discusses their use in making organic ferro- and ferrimagnetic materials and magnetically bistable systems exhibiting a hysteretic memory effect. The focus is on thiazyl and selenazyl radicals 1,2,3,5-dithia- (DTDAs) and 1,2,3,5-diselenadiazolyls (DSDAs) as well as the radical-anion formed from the quintessential electron acceptor 7,7´,8,8´-tetracyanoquinodimethane (TCNQ). The second part of the thesis summarizes the research published in the four original journal articles associated with this work. It details the synthesis and characterization of new pyridyl-substituted DTDA and DSDA radicals and their N-alkylation to the corresponding radical-cations. The cations were subsequently combined with the radical-anion of TCNQ to generate radical-ion salts, leading to the realization of room-temperature hysteretic magnetic bistability owing to the reversible association of monomeric TCNQ radicals to weakly C–C σ-bonded dimers. Consequently, a systematic study of substituent, solvent, and atom-to-atom replacement effects on the solid-state structure and properties of the synthesized salt was carried out, providing insight into designing a new type of multicomponent functional molecular materials.

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M.Sc. Anni Taponen defends her doctoral dissertation “Radical-Ion Salts based on Thiazyls and Tetracyanoquinodimethane: Hysteretic Magnetic Bistability in a Multicomponent System". on 24 March 2023 at 12 noon. Opponent Professor Delia Haynes (Stellenbosch University, South Africa) and custos Professor Heikki Tuononen (Ä¢¹½Ö±²¥). The doctoral dissertation is held in English.