One-End-Truncated Au52 and Au70 Quantum Rods: High-Quantum-Yield NIR-II Emitters With Aspect-Ratio-Dominated Photophysics.

Precise control over absorption/emission in NIR-II (1000-1700 nm) is essential for advancing photonic technologies. Atomically precise gold quantum rods (QRs) provide a structurally well-defined platform for fine-tuning NIR-II anisotropic excitonic behavior at the atomic level. In this study, we report Au52(PET)38 and Au70(PET)50 (PET = 2-phenylethanethiolate) as members of a distinct branch of Au QRs with one-end-truncated kernel topology. The Au52 and Au70 exhibit NIR-II absorption at 1032 and 1275 nm and nanosecond fluorescence at 1100 and 1360 nm, respectively. Their high quantum yields (20.9% for Au52 and 14.8% for Au70) together with high brightness (5.6 × 104 M-1 cm-1 for Au52 and a similar order of magnitude for Au70) substantially exceed those of most molecular NIR-II dyes, highlighting their promise as efficient inorganic NIR-II fluorophores. Comparative analysis across two structurally distinct Au QR families, including one-end-truncated and double-pointed rods, reveals that the longitudinal absorption and emission peak wavelengths, as well as the fluorescence linewidths, follow a common aspect-ratio-dependent scaling relation, suggesting length-dependent modulation of the ground- and excited-state electronic structure. These findings uncover a hierarchical interplay between rod elongation and kernel topology in defining NIR-II excitonic behavior and expand the structural design space of atomically precise QRs.