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.