Water-Soluble Trityl Radicals for Fluorescence Imaging

Abstract

Stable tris(trichlorophenyl)methyl radicals have gained interest as all-organic bioimaging agents combining fluorescent and paramagnetic properties. However, cellular uptake has so far only been reported for nanoparticles, because molecular hydrophobic trityl radicals are not soluble in aqueous media. Here, we report the synthesis and characterization of new water-soluble tris(trichlorophenyl)methyl radical derivatives exhibiting red doublet emission. Solubility in water is achieved through functionalization with oligoethylene glycol (OEG) chains. The emission behavior of OEG functionalized trityl radicals is studied in polar environments. Donor-functionalization with carbazole evokes a charge-transfer excited state that is efficiently quenched in polar solvents. In contrast, click-reaction mediated attachment of OEG-azide and trityl acetylene furnishes a triazole functionalized radical with locally excited states and emission in water. Confocal fluorescence microscopy proves successful uptake of the material by macrophages in cell culture, showing the potential of our water soluble trityl radical for fluorescence bioimaging.

A water-soluble luminescent tris(2,4,6-trichlorophenyl)methyl radical-carbazole dyad

“…32,34,35 The methoxy group was converted to a hydroxyl group with BBr 3 and reacted with tosylated polyethylene glycol (Ts-mPEG12) to obtain HTTM-PEG1 and HTTM-PEG3. 32,33,37 Obtained precursors were treated with KOtBu and then subsequently oxidized with p -chloranil to obtain the radicals. Precursors were characterized using 1 H NMR spectroscopy, 13 C NMR spectroscopy, MALDI-TOF-MS, and elemental analysis.…”

“…A few TTM s attached to the water-soluble or hydrophilic group have already been reported. 33–37 However, to our knowledge, a compound that shows water-solubility, luminescence, and paramagnetic relaxation enhancement (PRE) effects simultaneously has never been reported.…”