Tuning Fluorescence Properties of BIM Probes via Clay Integration: Targeting Rifampicin with improved selectivity.

The incorporation of photoactive organic dyes into layered inorganic materials enhances their optical and chemical properties, making them ideal for sensing applications. In this study, Bisindolyl methane (BIM)-based neutral probes were integrated with bentonite clay to explore their sensing capabilities. Probe 1 (unoxidized BIM) and Probe 2 (oxidized BIM) generally exhibited quenched luminescence in solution due to intramolecular rotations. Embedding Probe 1 within bentonite interlayers or adsorbing it onto the clay surface immobilized its conformation, restricting intramolecular rotations through planarization and significantly enhancing fluorescence emission. Conversely, rigid Probe 2, adsorbed predominantly on the clay surface, showed fluorescence quenching. Photophysical studies confirmed that the intercalation of Probe 1 into the clay induced unique planarization compared to its behavior in solution. The 1.clay composite exhibited selective fluorescence quenching and a red-shifted emission band upon interaction with rifampicin. This suggests that rifampicin displaced the probe from the clay interlayers into solution via strong hydrogen bonding with the clay's hydroxyl groups. Additionally, Probe 1 demonstrated higher selectivity for rifampicin over other tuberculosis drugs. These findings underscore the potential of the 1.clay composite as a highly selective, efficient sensing platform for rifampicin detection in clinical diagnostics and therapeutic drug monitoring.