SiO₂ encapsulated nanofluorophor: Photophysical properties, aggregation induced emission and its application for cell mitochondria imaging

An organic fluorescent 1,8-naphthalimide derivative (NI-1) was designed and synthesized. Its photophysical properties were systematically investigated by a series of spectroscopic and theoretical methods. The twisted intramolecular charge transfer (TICT) was proved within NI-1 in various solutions. After adding H₂O into its CH₃CN solution, the aggregation induced emission (AIE) of NI-1 occurred, during which the enhanced green-yellow fluorescence and quantum yield up to 0.62 were monitored. In addition, SiO₂ was used to coat on the surface of NI-1 to fabricate the composite nano structure (NI-1@SiO₂). This nanomaterial not only qualifies AIE-active characteristic, but also exhibits remarkable anti-photobleaching ability and good biocompatibility. The NI-1@SiO₂ can go through the cell membrane and specifically light up the mitochondria. The cellular uptake mechanism studies revealed that the energy-dependent cell uptake mechanism was responsible for the NI-1@SiO₂ entering cells. The NI-1@SiO₂ could be utilized as an efficient AIE-active fluorescent material and mitochondria imaging reagent.