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.