Charge Transport and Magneto-Responsive Properties of Open-Shell Single Crystals

Nonconjugated open-shell molecules are promising in a host of organic electronic and spintronic applications due to their abilities to conduct charge and provide magneto-responsive behavior. These properties generally arise due to the radical moieties present in their molecular design. Crystalline materials contain highly ordered molecular packing; this facilitates charge transport and often useful optical properties. In addition, liquid crystalline (LC) materials can exhibit structural transitions due to applied stimuli. Here, the relationship between the crystalline and LC structures and the resultant charge and spin transport properties is detailed for a class of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) benzoates with systematically tailored molecular structures. Specifically, five distinct molecules were synthesized by using a one-step esterification reaction. Of these five materials, three displayed LC behavior with distinct mesophases, while two formed single crystals with ordered molecular packing. During the evaluation of the materials in testbed devices, one of the single crystalline materials exhibited a room temperature conductivity of ∼15.6 S m–1, along with a 100% magnetoresistance at 10 K with a field strength of 2 T. In this way, the relationships between molecular design and the end-use magneto-responsive charge transport were established for these emerging radical materials.