Design of multi-functional AIEgens: tunable emission, circularly polarized luminescence and self-assembly by dark through-bond energy transfer

Abstract

A pair of chiral R/S-TPE-BINOL derivatives with dark resonance energy transfer was facilely synthesized by coupling of a tetraphenylethylene (TPE) derivative, BODIPY dye and R/S-1,1′-bi-2-binaphthol (BINOL), where TPE not only was selected as a dark energy donor, but also can endow the target molecules with aggregation-induced emission (AIE) characteristics; BODIPY served as an energy acceptor; BINOL, one of the most popular axially chiral compounds, was employed as a chiral source. Due to the chiral feature of R/S-TPE-BINOL, obvious CD and CPL signals were observed in the solution and aggregated states. Generally, for organic dyes, high dissymmetric factor (g_em) values are often accompanied by low emission efficiencies. To improve emission efficiency, an effective strategy of dark through-bond energy transfer was adopted. This method makes it possible to avoid fluorescence leakage originating from donor emission. The energy of TPE can be completely transferred to the BODIPY unit before non-radiative relaxation with an energy transfer efficiency of up to 99% and a high quantum yield of 91%. Remarkably, these enantiomers could self-assemble into bowl-like hollow microspheres in a mixed solvent of THF/water to give a stable fluorescent suspension with tunable emission from the green to yellow region. Moreover, TPE-BOD was selected as the fluorescent probe for specific staining of lipid droplets in living cells.