Red-emitting tetracoordinate organoboron chelates : synthesis, photophysical properties, and fluorescence microscopy

Abstract

Seven tetra-coordinate organoboron fluorophores with hetero-biaryl N,O or N,N chelate ligands were prepared and photophysically characterized (in toluene). The electronic variation of the heteroaromatic moiety provided a means for the fine-tuning of the UV/vis-absorption and emission spectra. In the most interesting cases the spectra were re-shifted to maximum absorb-ance at wavelengths longer than 500 nm and emission maxima between 620 and 660 nm. The pronounced intramolecular charge-transfer character of the dyes yielded large Stokes shifts (3500–5100 cm–1), while maintaining appreciable fluorescence quantum yields of up to 0.2 for emission maxima longer than 600 nm. The lipophilic character of the dyes enabled their application as stains of vesicle substructures in confocal fluorescence microscopy imaging.