Sterically Crowded Hexaterpyridyl-BODIPY: A Multiresponsive Far-Red Emissive AIE-Active Probe for Zn(II) Recognition and Biological Applications

Abstract

Sterically crowded aggregation-induced emission (AIE)-active fluorophores provide a powerful approach to constructing multifunctional platforms for sensing and bioimaging. Herein, we describe the rational design and synthesis of a highly crowded hexaterpyridyl-functionalized BODIPY, obtained through hexabromination of the BODIPY core followed by Suzuki-Miyaura coupling with terpyridyl boronic acid derivatives. Spectroscopic characterization confirms the structure, while the installation of six terpyridine units at the alpha/beta positions generates substantial steric crowding, leading to pronounced AIE behavior, far-red emission, cooperative metal-ion coordination, and efficient cellular imaging. Systematic aggregation studies in THF/water mixtures reveal significant fluorescence enhancement correlated with the formation of well-defined spherical nanoaggregates, as confirmed by TEM and SEM analyses. The hexaterpyridyl-BODIPY further exhibits selective Zn(II) recognition with distinct fluorescence responses. Comparative studies with alpha,alpha- and beta,beta-diterpyridyl analogs emphasize the critical role of multiligand steric crowding in tuning aggregation, photophysical properties, and biological performance. Notably, the hexaterpyridyl derivative shows efficient cellular uptake, bright intracellular fluorescence, excellent biocompatibility in normal and cancer cell lines, and enhanced phototoxicity compared to its counterparts. DFT calculations elucidate the structure-property relationships, establishing a versatile molecular design strategy that integrates AIE, metal-ion sensing, and bioimaging within a single BODIPY scaffold.