Highly Emissive AIEgens with Multiple Functions: Facile Synthesis, Chromism, Specific Lipid Droplet Imaging, Apoptosis Monitoring, and In Vivo Imaging

The development of new luminescent materials has allowed us to gain new knowledge and opened a new opportunity for scientific achievement and social development. In this work, luminogens, namely, (4-pyridinyl)-phenyldiphenylamine (TPAP) and 3-diphenylamino-6-(2-pyridinyl)phenyldiphenylboron (TPAP-BB), were synthesized in satisfactory yields through convenient synthetic routes and their properties were systematically investigated. These luminogens exhibited a moderate fluorescence quantum yield in tetrahydrofuran (14.6% for TPAP and 49.0% for TPAP-BB), whereas their values in thin films were much higher (69.4% and 88.4%), demonstrating a phenomenon of aggregation-induced emission (AIE). Moreover, TPAP-BB not only exhibited piezo-chromism (its emission color could be tuned repeatedly by grinding–heating cycle because of the transformation between crystalline and amorphous phases) but also showed on–off light emission process by repeatedly fuming with acid and ammonia vapor. Furthermore, TPAP-BB exhibited impressive high photostability and low toxicity to living cells. It could specifically stain lipid droplets (LDs) in live HeLa cells with higher signal-to-noise ratio than Nile Red, a commercial LDs agent. This dye could also be applied for real-time monitoring of cell apoptosis and in vivo imaging in Medaka fish. Such results were expected to create enthusiasm to generate new AIE luminogens for further technological applications.