Assembly, Two-Photon Absorption, and Bioimaging of Living Cells of A Cuprous Cluster

A novel cuprous­(I) cluster Cu₄I₄L₄ (L = (E)-(4-diethylanilino-styryl)­pyridine) bearing strong two-photon absorption (TPA) was obtained using a facile assembly method, and the crystal structure has been determined. Quantum chemical calculations using time-dependent density functional theory (TD-DFT) reveals that the combination of the organic ligands with the three-dimensional Cu₄I₄ core extends the electronic delocalization in the cluster, leading to strong two-photon absorption action. The TPA cross sections (Φσ₂) of Cu₄I₄L₄ were enhanced with increasing polarity of solvents, which is quite different from the solvent effects on TPA in the literature. Compared to its free ligand, the cluster Cu₄I₄L₄ exhibits larger peak TPA cross sections in the near-infrared region, longer fluorescence lifetimes, higher quantum yield and photostability, lower cytotoxicity, and brighter two-photon fluorescent (TPF) bioimaging. These integrated advantages make it desirable to be applied as a two-photon fluorescent probe for labeling the nucleic acids in live cells.