N-Doped Nonalternant Nanoribbons with up to 29 Linearly-Fused Rings and High Charge-Carrier Mobilities

The synthesis of nonalternant graphene nanoribbons (GNRs)-carbon-based nanostructures featuring fused pentagonal or heptagonal rings that disrupt hexagonal symmetry-has remained a significant challenge despite their unique electronic properties, such as tunable bandgaps and topological states. Unlike conventional alternant hydrocarbons (e.g., benzene-derived systems), nonalternant architectures exhibit distinct electron confinement effects, making them promising for nanoscale optoelectronics and quantum materials. However, achieving precise control over their length, solubility, and structural regularity has had limited progress. Herein, we report a versatile solution-phase synthesis of a novel family of structurally precise N-doped nonalternant nanoribbons (NRs: NR-11 to NR-29) through pentagon annulation of pyrazino[2,3-g]quinoxaline and naphthalene subunits terminated with triptycene end-caps. The longest one comprises 29 linearly fused rings (particularly including 10 pentagonal rings), setting a new length record of 7.18 nm among the soluble nonalternant NRs reported to date. Strategic incorporation of triptycene end-caps and alkoxyphenyl substituents into their molecular backbones confers high solubility and a unique 3D configuration, enabling comprehensive solution-phase structural characterization and systematic investigation of length-dependent optoelectronic properties. Employing terahertz (THz) spectroscopy, we infer high intrinsic charge carrier mobilities in nonalternant nanoribbons, reaching up to ∼2000 cm² V^-1 s^-1, highlighting this novel family of nanoribbons as promising candidates for future nanoelectronic applications.