Evolution of coherent vibrations in atomically precise gold quantum rods with periodic elongation

The coherent vibrational dynamics of gold nanorods with varying aspect ratios have been extensively studied by time-resolved spectroscopy to reveal their mechanical properties, but quantum-sized rods (transverse diameter < 2 nanometers) remain unexplored. Here, we present a comprehensive study on the coherent vibrations of atomically precise gold quantum rods with distinct energy gaps (0.6 to 1.3 electron volts), all sharing the same radial dimension but with increasing aspect ratios. Time-resolved spectroscopy reveals ultrafast internal conversion and intersystem crossing, along with oscillatory features superimposed on transient signals that unveil coherent vibrational dynamics. Two dominant modes are identified: a longitudinal mode scaling with rod length and a transverse mode independent of aspect ratio. Theoretical simulations support these findings and clarify the structural origins of the observed vibrational behavior. Our study provides a framework for designing atomically precise gold quantum rods with tailored optical and vibrational properties, advancing the understanding and application of anisotropic quantum materials.