Pendant and π-Conjugated Organic Polyradicals

One of the potential candidates to realize a very high-spin and purely organic-derived molecule is a π-conjugated linear polymer bearing multiple pendant radical groups that are attached to a π-conjugated backbone to yield a non-Kekulé structure (Scheme 1). For some of these pendant polyradicals, theoretical studies have predicted an intrapolymer and through-bond ferromagnetic interaction between the pendant spins, since such a π-conjugated backbone acts as a ferromagnetic coupler (FC) [1]. The pendant-type polyradicals possess the following advantages over the cross-conjugated-type polyradicals that are described in other chapters of this book, such as oligo(phenylenecarbene)s (Chapters 11 and 12) [2] and oligo(triarylmethyl)s (Chapter 17) [3], whose FCs were divided by the spin sites. First, a ferromagnetic spin interaction occurs through the π-conjugated backbone, and potentially even works over a long conjugation length (Scheme 1). That is, the spin coupling is not sensitive to the spin defects that are unavoidable for macromolecular polyradicals. This is in contrast to the cross-conjugated polyradicals, where the spin defect breaks down their π-conjugations. Second, a great number of spins is accumulated along one backbone or within one molecule. The spins are expected to interact among not only their neighboring spins but also with more remote spins. Third, various chemically stable radical species can be introduced to a polyradical as the pendant Scheme 1https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203748503/a91773da-41e5-4373-adb7-d7d4102181d5/content/chem227.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> group. The resultant polyradical has substantial stability and is easily handled, e.g., at room temperature and under air. Such feasibility would be indispensable for the future application of magnetic organics as materials. Additionally, precursors of this type of polyradical may be synthesized via one-pot polymerization and are soluble in common solvents; these characteristics are very favorable for obtaining and processing well-characterized samples to study.