Electrical Properties of Radical-containing Monomers and Their Application in Topochemically Polymerized Macromolecules

Nonconjugated radical-based materials have emerged as compelling candidates for electrical conductors due to their stable open-shell sites. However, most of the research focus has remained on amorphous radical polymers, with limited attention paid to the impact of molecular packing on charge transport properties. Therefore, we designed, synthesized, and crystallized two nitroxide-based radical molecules, hexa-2,4-diyne-1,6-diyl bis((1-hydroxyl-2,2,6,6-tetramethylpiperidin-4-yl) carbamate) (TEMPO-DY-TEMPO) and 5-phenylpenta-2,4-diyn-1-yl (1-hydroxyl-2,2,6,6-tetramethylpiperidin-4-yl) carbamate (DY-TEMPO). With the potential of diynes for intrinsic highly ordered alignment through topochemical reaction, these molecules, with differing symmetries, were employed to evaluate the physical phenomena associated with electrical conductivity in single-crystal studies. DY-TEMPO, with its enhanced radical proximity (~4.838 Ǻ), shows an impressive electrical conductivity of ~91 S m⁻¹ at ambient temperature with no doping and a magnetoresistance value of 140% at 10 K. Thus, open-shell small molecule single crystals were developed with superior charge transport capabilities through optimized packing of active radical moieties. Furthermore, these results afford valuable insights into the potential design of future crystalline polymers through topochemical polymerization for the next generation of nonconjugated radical electrical conductors.