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.