Directional Electron Transfer in Chromophore-Labeled Quantum-Sized Au₂₅ Clusters: Au₂₅ as an Electron Donor

Abstract

Novel Au25(C6S)17PyS clusters (pyrene-functionalized Au25 clusters) showing interesting electrochemical and optical properties are synthesized and characterized. Significant fluorescence quenching is observed for pyrene attached to Au25 clusters, suggesting strong excited-state interactions. Time-resolved fluorescence upconversion and transient absorption measurements are utilized to understand the excited-state dynamics and possible interfacial electron- and energy-transfer pathways. Electrochemical investigations suggest the possibility of electron transfer from Au25 clusters to the attached pyrene. Fluorescence upconversion measurements have shown faster luminescence decay for the case of pyrene attached to Au25 clusters pointing toward ultrafast photoinduced electron/energy-transfer pathways. Femtosecond transient absorption measurements have revealed the presence of the anion radical of pyrene in the excited-state absorption, suggesting the directional electron transfer from Au25 clusters to pyrene. The rate of forward electron transfer from the Au25 cluster to pyrene is ultrafast (∼580 fs), as observed with femtosecond fluorescence upconversion and transient absorption.