Calix[4]arene-Naphthalimide Fluorescent Sensors for Cu²⁺ and F⁻ Ions: Synthesis and Biological Imaging

Introduction: Calix[n]arenes can be selectively functionalized more easily than other cyclic supramolecules such as crown ethers and cyclodextrins. 1,8-Naphthalimide derivatives of calix[ 4]arenes are very important and versatile fluorophores widely used in fluorescence detection due to their high absorption coefficients, strong fluorescence, high quantum yields, large Stokes shifts, excellent photostability. Materials and Methods: Two Calix[4]arene-based fluorescent probes were synthesized for the detection of Cu2+ and F-. The fluorescence properties of the compounds were evaluated in the presence of various cations and anions using spectroscopic techniques. Their cytotoxicity was tested in Hep-2 and HeLa living cells. Results: The synthesized calix[4]arene derivatives were evaluated in the presence of various cations and anions using different spectroscopic and analytical techniques. In the tests, the fluorescence intensity of 7 decreased significantly in the presence of Cu2+ or F-. A similar quenching effect was observed for 6 only in the presence of Cu2+. The cytotoxic properties of calix[4]arene derivatives were evaluated against Hep-2 and HeLa living cells. The results showed significant cytotoxicity of compounds 6 and 7. Discussion: Confocal microscopy studies revealed that these compounds exhibited strong intracellular fluorescence, indicating efficient cellular uptake by cells. In the presence of Cu2+ or F-, the fluorescence intensity of the diamide derivative decreased significantly, which was attributed to the complexation effect between the ligand and the corresponding ions. Conclusion: Monoamide derivative 6 has the potential to be a fluorescent sensor for Cu2+, and diamide derivative is a fluorescent sensor for Cu2+ and F- ions. Cells treated with compounds 6 or 7 exhibited high intracellular fluorescence.