Phosphorescent cationic iridium(iii) complexes dynamically bound to cyclodextrin vesicles: applications in live cell imaging.

Frauke Schibilla,Volker Gerke,Anna Lívia Linard Matos,Boyi Song,Eli Zysman-Colman,Diego Rota Martir,Anna Holthenrich,Bart Jan Ravoo,David Grill

doi:10.1039/c8sc02875c

Abstract

We report cationic Ir(iii) complexes functionalized with adamantyl groups designed to bind to β-cyclodextrin vesicles (CDV) with high affinity (K a = 1 × 106 M-1). The emission of the complexes is tuned by changing the nature of the cyclometalating ligands. The host-guest adduct of CDV and Ir(iii) complexes shows increased and significantly blue-shifted emission due to the lower mobility of the Ir(iii)-complexes residing in the less polar environment of the vesicle surface. Ir(iii)-decorated CDV are efficiently taken up by cells and can be used in live cell imaging. The CDV act as carriers to transport the phosphorescent complexes into cells where they selectively stain mitochondria.

Highlights

Cationic Ir(III) complexes containing two bidentate cyclometalating ligands (C^N, e.g., 2-phenylpyridinato, ppy) and one bidentate diimine ligand (N^N, e.g., 2-20-bipyridine, bpy) are a family of phosphorescent materials featuring microsecond emission lifetimes (sPL), high photoluminescence quantum yields (FPL), wide color tunability as a function of ligand design, and high photo- and chemostability.[1,2] Cationic Ir(III) complexes are widely used in organic light-emitting diodes (OLEDs),[3,4,5] chemosensing systems[6,7,8] and bioimaging.[9,10,11] Bioimaging, in particular the visualization of speci c processes and structures in live biological specimens such as cells, has greatly bene tted from the introduction of uorescence-based imaging methods together with tools to deliver such uorescence probes into cells
In PB, both 1a and 1b emit via a mixed CT state that was assigned based on a positive solvatochromic behavior (ESI, Fig. S4†); in apolar PhMe, the emission becomes structured and more ligandcentered, with maxima that align to those observed during the addition of CD vesicles (CDV) to the complexes
We have shown that two cationic Ir-complexes bearing adamantane anchoring units bind strongly to CDV giving rise to enhanced emissions that are shi ed to higher energies compared to measurements in aqueous solution

Summary

Introduction

Cationic Ir(III) complexes containing two bidentate cyclometalating ligands (C^N, e.g., 2-phenylpyridinato, ppy) and one bidentate diimine ligand (N^N, e.g., 2-20-bipyridine, bpy) are a family of phosphorescent materials featuring microsecond emission lifetimes (sPL), high photoluminescence quantum yields (FPL), wide color tunability as a function of ligand design, and high photo- and chemostability.[1,2] Cationic Ir(III) complexes are widely used in organic light-emitting diodes (OLEDs),[3,4,5] chemosensing systems[6,7,8] and bioimaging.[9,10,11] Bioimaging, in particular the visualization of speci c processes and structures in live biological specimens such as cells, has greatly bene tted from the introduction of uorescence-based imaging methods together with tools to deliver such uorescence probes into cells. Complexes 1b and 2b show signi cantly more intense, broad and unstructured green emission at 525 nm in PB (ESI, Fig. S1†), which is the result of the inclusion of the electron-withdrawing uorine atoms on the cyclometalating ligands.[37] The preparation of the CDV is described in the ESI.† Titration of non-emissive CDV (1–100 mM) into a constant concentration of Ir-complex (10 mM) resulted in changes in both the emission intensity and pro le (Fig. 3).

Results

Conclusion