Mitochondria Targeting Fluorescent Probes Based on through Bond‐Energy Transfer for Mutually Imaging Signaling Molecules H 2 S and H 2 O 2

Reactive signaling molecules participate in varieties of biochemical reactions, and methods to detect their mutual existence and crosstalk are in urgent demand. A benzothiadiazole‐based handle was designed to fluorescently respond to the co‐existence of H 2 S and H 2 O 2 under pseudo‐physiological conditions on a basis of a thiyl‐radical‐mediated mechanism that accounts for the rapid and efficient domino‐like reaction processes. Then the handle motif was attached to a rhodamine moiety by means of an ethynylene linkage, and achieved a significant H 2 S–H 2 O 2 mutual response in the mitochondria of living cells. Theoretical calculations supported that a through bond energy transfer mechanism contributes to the drastic fluorescence response.