A highly sensitive fluorescence probe based on pyrene-pyrazole-imidazole conjugate: exploration of solvatochromism, selective detection of iodide ion, DFT analysis and cell imaging studies

Iodide ions are biologically important naturally occurring anions in the human body. In this study, we designed and synthesized a novel pyrene-pyrazole-imidazole conjugate (PPIC) fluorescent probe using a microwave-assisted multicomponent reaction. The PPIC probe was characterized by standard analytical methods, including mass, IR, 1 H NMR, 13 C NMR spectrometry, and elemental analysis. Its Optical characteristics, such as light absorption and emission Stokes shift, and quantum yield, aggregation-induced emission were examined in various solvents and showed notable solvatochromic behavior. PPIC has selectively detected iodide ions (I − ) through a fluorescence turn-off response, while other competing anions caused negligible interference. Linearity was evident in the relationship between iodide concentration and fluorescence intensity over the range of 0–12.5 μM, with an R 2 value of 0.996. The LOD for I − ion was found to be 3.60 μM which is lowest among this class of derivatives. Fluorescence life-time studies revealed a shorter decay time after iodide addition, indicating a dynamic quenching mechanism. In addition, PPIC successfully detected iodide ions in iodide-containing catalysts such as KI and TBAI, demonstrating its practical utility in aqueous media. The Job's plot analysis confirmed the 1:1 binding stoichiometry of the PPIC–I − complex, while DFT calculations supported the proposed sensing mechanism involving FMO, MEP, NBO, and QTAIM analyses, which revealed the electronic redistribution and intermolecular interactions governing fluorescence quenching via ICT mechanism. Moreover, cell imaging studies in the human breast cancer (MCF) cell line revealed that the newly developed PPIC probe produced bright blue fluorescence, exhibited excellent live-cell imaging capability. The probe showed a concentration-dependent lower cell viability associated with an IC 50 of 34.5 μg/mL and may have potential in cancer theranostics. Overall, these results indicate that the synthesized pyrene-pyrazole-imidazole conjugate (PPIC) is a selective and sensitive Iodide-responsive fluorescent sensing system with promising bioimaging potential.