AIE (aggregation-induced emission)-active TPE derivatives, TPE-TPP, TPE-MitoR and TPE-IQ are contemplated. These specific TPE derivatives are useful as fluorescent agents for mitochondrial imaging and as apoptosis inducers. Possessing high specificity to mitochondria, superior photostability and appreciable tolerance to microenvironment change, TPE derivatives are well-suited imaging agents for mitochondrial targeting and morphological change tracking. Because of their synthetic flexibility, TPE derivatives can be further modified as dual-functional probes for an array of applications such as sensing of ROS, metal ions, or pH change in mitochondria.