Length-Controlled Synthesis of Graphene Nanoribbons

Graphene nanoribbons (GNRs) have emerged as promising materials for next-generation electronic, optoelectronic, and quantum devices due to their tunable bandgaps and edge-dependent properties. A critical challenge in their integration lies in the ability to precisely control their length and ensure structural uniformity. This review highlights three major synthetic strategies developed to address this challenge: living polymerization, conventional iterative synthesis, and protecting group-aided iterative synthesis (PAIS). Living polymerization approaches enable scalable access to GNRs with narrow length distributions, although they rely on specialized monomers and catalyst design to maintain a living character. The conventional iterative synthesis strategy provides a pathway for the preparation of specific GNRs with precise length, but it is still not possible to synthesize general GNRs with a desired length or a well-defined heterogeneous monomer sequence. The PAIS strategy stands out, allowing atomic-level control over GNR length, width, edge structure, and heterojunction placement. Iterative methods offer unparalleled atomic precision and architectural flexibility but are labor-intensive and limited by solubility constraints. Each method presents complementary advantages and trade-offs. Future advancements are expected to stem from hybrid synthetic platforms, catalyst innovations, and programmable template design, ultimately enabling deterministic control over GNR structures and properties for device applications.