Ultra-narrow donor-acceptor nanoribbons

Donor–acceptor (D–A) architectures underpin many high-performance conjugated polymers but remain largely unexplored in atomically precise nanoribbons. Here, we report the on-surface synthesis of ultra-narrow D–A nanoribbons using two complementary brominated precursors based on the electron donor peri-xanthenoxanthene and the acceptor anthanthrone. High-resolution scanning tunnelling microscopy, non-contact atomic force microscopy and scanning tunnelling spectroscopy reveal submolecular structural and electronic features of the resulting nanoribbons. Homopolymerisation of each precursor yields structurally well-defined donor-only and acceptor-only nanoribbons, whose electronic character strengthens with length. Co-deposition of both precursors produces mixed D–A nanoribbons with tuneable electronic structures governed by monomer sequence. The spatial character and energetic alignment of their frontier orbitals match gas-phase DFT calculations, while a simplified linear combination of molecular orbitals model captures dominant trends. This bottom-up synthetic strategy enables precise control over nanoribbon composition and functionality, offering a versatile platform for engineering π-conjugated nanostructures with tailored optoelectronic properties.