Aggregation-Induced Emissive Copper(I) Complexes for Living Cell Imaging

Phosphorescent
binuclear copper­(I) complexes [Cu2(BrphenBr)2(Ph2P­(CH2)nPPh2)2]­(ClO4)2 with different
conformations are obtained by reaction of [Cu­(NCCH3)4]­ClO4, 3,8-dibromo-1,10-phenanthroline (BrphenBr),
and corresponding diphosphine ligands, where n =
1, 4, 5, and 6 in complexes Cu-1, Cu-2, Cu-3, and Cu-4, respectively. Complex Cu-4 exhibits both
the eclipsed and the staggered conformations of 18-membered Cu2C12P4 metallacycles in a 1:1 ratio in
the crystal structure. All complexes are very stable to air and moisture
in the solid state because of the high level of protection of all
the Cu­(I) centers, N and P atom centers resulting from the close contact
of BrphenBr and diphosphine ligands, and what is more important is
that there exist very soft P donors and the chelating effect of aromatic
N atoms. The ESI-MS result through changing the collision cell energy
from 0 to 20 eV suggests that the corresponding [Cu2(Ph2P­(CH2)nPPh2)2]2+ cations are the thermodynamically stable
species, while [Cu2(BrphenBr)2(Ph2P­(CH2)nPPh2)2]­(ClO4)2 are stable products in crystallization
kinetics in solutions. All complexes Cu-1–Cu-4 display good aggregation-induced
phosphorescence emission (AIPE) behavior in CH2Cl2/hexane mixed solvents, which are suggested to arise from restriction
of intramolecular rotation. Aggregation-induced emission (AIE) of
complexes Cu-1–Cu-4 in PBS/DMSO (99:1, v:v) is used for living HeLa cell imaging
successfully with green intracellular emission image.