A novel pyrene-based aggregation induced enhanced emission active Schiff base fluorophore as a selective “turn-on” sensor for Sn2+ ions and its application in lung adenocarcinoma cells

Abstract

Schiff bases are an important class of compounds that are highly instrumental in complex formation as well as act as sensors for various metal ions. Herein, 1-aminopyrene was reacted with 5-bromo-2-thiophene carboxaldehyde to synthesize a designed Schiff base, PY-SB (N-((5-bromothiophen-2-yl) methylene) pyrene-2-amine) as a condensation product. The authenticity of the synthesized Schiff base compound was established using 1H NMR, 13C NMR, IR and HRMS techniques. Among the optoelectronic investigations, the AIEE (Aggregation Induced enhanced emission) property of PY-SB was explored and it showed 24 folds enhancement in fluorescence intensity in tetrahydrofuran (THF) and water mixtures (50:50). AIEE results were further supported by DLS (Dynamic Light scattering) study. In addition, PY-SB was found to be a highly selective and sensitive tool for the “turn-on” detection of Sn2+ ion. The turn–on fluorescence of PY-SB is due to the PET-OFF process. The electron transfer from nitrogen to the pyrene ring is completely blocked due to the formation of a complex of PY-SB with insitu generated Sn2 species(PY-SB + Sn2), which causes PET-OFF. The detection limit and binding constant of PY-SB towards Sn2+ ion were found to be 5.4 µM, and 2 × 104 M−1, respectively. The stoichiometric study through Job’s plot reveals the development of 2:1 ratio (Sn2: PY-SB) of complexation which is further confirmed by DFT, ES-MS, 1H NMR and 13C NMR, SEM-EDX. To verify the sensing behavior of PY-SB in a biological system, in vitro studies on lung adenocarcinoma cells were successfully carried out and they showed similar behavior as seen in the cuvette study.