AIE-active Cyclen-BODIPYs as multiresponsive fluorescent probes for imaging in biological samples: Design and...

The aggregation-induced emission (AIE) effect opens up new opportunities and prospects for the development of organic light-emitting materials. By exploiting the intrinsic ability of boron-dipyrromethenes (BODIPYs) to form aggregates, we rationally designed water-soluble AIE-active dyes derived from BODIPY fluorophores by their modification with azamacrocyclic units. The most AIE-active cyclen-BODIPY derivatives 5a and 8a showed high fluorescence quantum yields and they were found to be sensitive to water content, viscosity, pH, and temperature with a "turn-on" fluorescence response. The DLS and SEM results showed that these compounds exist as nanoscale aggregates in aqueous solutions. A possible molecular arrangement of dye 5a in aggregates was rationalized using TD-DFT calculations. The biologically relevant metal ions, such as Li⁺, K⁺, Na⁺, and Mg²⁺, have no pronounced effect on absorption and emission spectra of the dyes 5a and 8a. In vitro confocal microscopy studies in HeLa cells demonstrated that dyes 5a and 8a successfully permeated the cell membrane and selectively labeled lysosomes. These findings suggest that cyclen-BODIPY derivatives hold promise for investigating lysosomal dynamics and function in living cells via fluorescence imaging.