Synthesis and Photophysical Properties of Light-Harvesting Gold Nanoclusters Fully Functionalized with Antenna Chromophores

The development of efficient light-harvesting systems is important to understand the key aspects of solar-energy conversion processes and to utilize them in various photonic applications. Here, atomically well-defined gold nanoclusters are reported as a new platform to fabricate artificial light-harvesting systems. An efficient amide coupling method is developed to synthesize water-soluble Au₂₂ clusters fully protected with pyrene chromophores by taking advantage of their facile phase-transfer reaction. The synthesized Au₂₂ clusters with densely packed 18 pyrene chromophores (Au₂₂–PyB₁₈) exhibit triple-emission in blue, green, and red wavelength regions arising respectively from pyrene monomer, pyrene excimer, and Au₂₂ emission, producing bright white light emission together. The photoluminescence of Au₂₂ is enhanced by more than tenfold, demonstrating that pyrenes at the periphery efficiently channel the absorbed energy to the luminescent Au₂₂ at the center. A combination of femtosecond transient absorption and anisotropy measurements of Au₂₂–PyB₁₈ explicitly reveals three main decay components of 220 fs, 3.5 ps, and 160 ps that can be assigned to energy migration between pyrenes and energy transfer processes from pyrene monomer and excimer to the central Au₂₂, respectively.