Magnetoresistance effect of pyridine-capped <i>s</i>-indacene-based conjugated radicals

Owing to their unique and tunable optoelectronic and magnetic properties, organic conjugated radicals have great potential in information storage and communication through modulating the molecular spin states. However, few electronic/spintronic devices based on these materials have been reported to date due to various intrinsic constraints such as poor material stability and processability. In this work, we have synthesized a stable singlet ground state organic conjugated diradical 5,7-dimesityl-<i>s</i>-indaceno[1,2-<i>b</i>:7,6-<i>b</i>']dipyridine (mNIF) with narrow band gap (1.16 eV) and small singlet-triplet energy gap (Δ<i>E</i>_S-T = -1.05 kcal mol^-1). mNIF showed good ambient stability and processability, and we have successfully fabricated a single ferromagnetic electrode device based on it with the structure of Ti/Au/mNIF/Co/Au. Distinct interface magnetoresistance effects were observed when the device was tested at different temperatures, which were attributed to the temperature anisotropy of the interface magnetic layer due to the small Δ<i>E</i>_S-T. Nevertheless, no interface magnetoresistance effect was observed in the device based on its <i>syn</i> analogous closed-shell molecule. Our work demonstrates the potential application of organic conjugated radicals in quantum memory.