Conjugated Star Polymers from Multidirectional Suzuki–Miyaura Polymerization for Live Cell Imaging

Abstract

Comparative Suzuki–Miyaura coupling polymerization (SMCP) studies with initiators generated in situ from 4-iododiphenylether (1), 4,4′-diiododiphenylether (2), 1,6-bis(4-iodophenoxy)hexane (3) and 1,4-bis(4-iodophenoxy)cyclohexane (4) result in bidirectional growth for 2, versus preferred monodirectional growth for 3 and 4 with their aliphatic spacers, in agreement with a “chain walking” of the metal along the aromatic system. Multidirectional controlled SMCP was initiated on a 1,6,9,14-tetra(4-iodophenoxy)-N,N′-(2,6-diisopropylphenyl) terrylene-3,4:11,12-tetracarboxidiimide (TDI-ArI4) near-infrared fluorescent dye as a tetrafunctional core. MALDI–TOF characterization and end group analysis reveal that four-armed polyfluorene-star-terrylenediimide (PF-star-TDI) polymers are formed with narrow molecular weight distributions (e.g., Mw/Mn = 1.29 at Mn = 1.8 × 104 g mol–1 from GPC). An efficient energy transfer results in a virtually exclusive NIR emission from the core upon excitation of the stars’ polyfluorene arms. Consequently, “doping” of self-stabilized nanoparticles (NP) from polyfluorene–poly(ethylene glycol) (PF–PEG) diblock copolymers with PF-star-TDI dye afforded particles with a bright emission in the red and NIR regime upon excitation at λexc = 380 nm. The utility of the “doped” particles for cell imaging was demonstrated by differentiation experiments with J774 macrophages and NIH-3T3 mouse fibroblast cells. In cocultures of both cell types, they can be differentiated by their emission color via confocal fluorescence microscopy due to their size-dependent uptake.