We report the design and synthesis of a novel cationic AIE-gen, i.e., (E)-TPEDEPy-DBz, which can be derived from a facile synthetic route. (E)-TPEDEPy-DBz is a stereo-pure isomer and shows evident AIE properties with yellow-greenish emission in the solid state (ΦF = 43.7%). Distinct from most of the ionic AIE-gens reported in the literature, which are usually exemplified by their water solubility and the capacity for interaction with charged biological species, (E)-TPEDEPy-DBz demonstrated moderate solvatochromism and evident mechanoluminochromism behaviours. The emission of (E)-TPEDEPy-DBz can be switched between yellow-greenish in the crystalline state to red-orange in the amorphous state by grinding and fuming treatments. Due to the AIE-characteristics, cationic modification and the thus-acquired water solubility, (E)-TPEDEPy-DBz performed as a sensitive fluorescent probe to detect DNA in Tris-HCl buffer solution. More importantly, (E)-TPEDEPy-DBz showed good membrane permeability and cell viability, and the potentiality to be used as a mitochondria-specific probe working in a fluorescence turn-on mode.