Deciphering the Temperature-Dependent Photophysical Properties of Atomically Precise Cu₆ Nanoclusters

Atomically precise copper nanoclusters (Cu NCs) have gained significant interest owing to their unique structures and diverse optical properties; however, the wet synthesis of Cu NCs with intense luminescence is a considerable challenge. Here, we developed a method to prepare atomically precise ultrasmall Cu6 NCs, capped by the 2,6-dimethylbenzenethiol (DMBT) ligand. The synthesized NCs were characterized by matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) analysis, and their compositional formula was determined to be Cu6(DMBT)5(dppe). Moreover, the electronic relaxation dynamics have been analyzed from temperature-dependent photoluminescence (PL) studies. This temperature-dependent study reveals that a 14 times increment of the PL intensity, along with the energy shift, occurs with lowering the temperature from 300 to 80 K. This result has been explained using the O'Donnell–Chen model, where we configured the involvement of the stretching vibrations of Cu(I)–S of the surface staple motifs. In consideration of the vibrational energy, temperature-dependent peak shift, and decay lifetimes, a direct relation with the relaxation dynamics of the NCs has been proposed. This work highlights the tuning of the photoluminescence and relaxation channels, which is helpful for nanothermometry devices.