Synthesis and aggregation properties of boron-dipyrromethene dyes conjugated with guanine units

Two boron-dipyrromethene dyes bearing a conjugated guanine unit (G-BODIPYs) 1 and 2 were synthesized and fully characterized. The self-assembly properties of these dyes were investigated by X-ray crystallography, H-1 NMR and UV-vis spectroscopy. As revealed by X-ray crystal structure studies, G-BODIPY 1 self-assembled into ribbon-like structures due to the intermolecular hydrogen bonding and pi-pi stacking interaction. Concentration-dependent H-1 NMR experiments confirmed the formation of hydrogen bonds of the guanine units in solution for both dye 1 and 2. In the presence of K+, the characteristic signals for the formation of cyclic G-quadruplex structures were observed in the H-1 NMR study. Aggregation of G-BODIPY dyes was further monitored by UV-vis absorption spectroscopy by varying the solvent polarity and temperature. H-type aggregates of dye 1, which was characterized by a new hypsochromically shifted absorption band with lambda(max) = 461 nm, was obtained. In the presence of K+, the enhancement of stability was observed for the H-aggregates of dye 1.