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

Abstract

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.

Synthesis, structures and aggregation-induced emissive properties of copper(I) complexes with 1H-imidazo[4,5-f][1,10]phenanthroline derivative and diphosphine as ligands

“…Complexes 4 and 5 exhibit various AIE colors changing from yellow-green to yellow. Similar AIE effect was also observed for the binuclear [Cu 2 (BrphenBr) 2 (Ph 2 P(CH 2 ) n PPh 2 ) 2 ](ClO 4 ) 2 (BrphenBr = 3,8-dibromo-1,10-phenanthroline) complexes with common features of twisted structures and freely rotatable peripheral aromatic moieties [30]. It's worth mentioning that yellow-green AIE luminescence of complex 4 contrasts markedly with the yellow emission in the solid state (see Figure 11), indicating that AIE colors depend on the different aggregation states dramatically.…”

“…Therefore, it is necessary and urgent to explore, design and synthesize noble-metal-free AIPE complexes. In this purpose, copper(I) complexes containing diimine and diphosphine ligands appear to be a good alternative [30].…”

“…Therefore, AIE phenomenon provides a new way for the application of Cu(I)-diimine-diphosphine systems as ''turn-on'' luminescent materials by taking the advantage of luminogenic aggregation through restriction of intramolecular motion in the aggregated state. We reported a series of mononuclear and binuclear Cu(I)-diimine-diphosphine complexes with good phosphorescent properties at room temperature [30, 34d, 35c], and the binuclear [Cu 2 (BrphenBr) 2 (Ph 2 P(CH 2 ) n PPh 2 ) 2 ](ClO 4 ) 2 (BrphenBr = 3,8-dibromo-1,10-phenanthroline) complexes exhibited good AIPE behavior and were further used for living cell imaging successfully [30]. …”

Synthesis, structure and solid luminescence of copper(I)–bromodiimine–diphosphine complexes

“…In DCM solutions, all complexes showed no obvious emission in air atmosphere due to the PL quenching by oxygen and the active intramolecular motions [13,15]. …”

“…Such distortion mainly depends on the chelating diimine and diphosphine ligands. [17], [Cu 2 (BrphenBr) 2 (Ph 2 P(CH 2 ) n PPh 2 ) 2 ](ClO 4 ) 2 (n = 1, 4, 5 and 6) and [Cu 2 (BrbpyBr) 2 (Ph 2 P(CH 2 ) n PPh 2 ) 2 ](ClO 4 ) 2 (n = 1, 4 and 5) [15,16]. Such larger dihedral angles imply that there exists larger repulsion between BrphenBr or BrbpyBr and the bulky BINAP or xantphos ligands, especially between BrbpyBr and diphosphine ligands.…”