Tetrazine, a benzene-like molecule with four embedded nitrogen atoms, has been identified as an ideal moiety to possess the aforementioned tunable fluorescence quenching properties. The quenched fluorescence emission can be fully recovered after the tetrazine quencher is controllably decomposed upon photoirradiation or through inverse electron demand Diels-Alder (iEDDA) reaction with strained alkene , alkyne , or isonitrile groups. The iEDDA reaction has been successfully employed as a bioorthogonal reaction that can selectively occur in the molecularly crowded environment inside biological systems. Consequently, tetrazine-based fluorogenic dyes have been extensively developed, with significant efforts aiming at enhancing their emission enhancement ratio (IAC/IBC, where IAC and IBC are the photoluminescence intensities after and before click reactions) by increasing tetrazine quenching efficiency. For example, initial studies started in the last decade focused on Förster Resonance Energy Transfer (FRET) or through-bond energy transfer (TBET) to direct n-π* emission quenching and ultrahigh IAC/IBC (>1000-fold) was achieved in blue to green probes via connecting fluorophore and tetrazine in proximity distance. Later on, red to nearinfrared turn-on emissions, which are challenging to attain through FRET or TBET-type quenching, were realized by employing Dexter energy transfer (DET), internal conversion (IC), and photo-induced electron transfer (PeT) directed by sophisticated control of molecular conformations. As a unique approach, molecular disaggregation upon iEDDA reaction was also applied to enhance the IAC/IBC of near-infrared (NIR) cyanine dyes. These tetrazinebased fluorogenic dyes have been successfully employed in bioorthogonal imaging of various cellular targets such as lipids, sugars, proteins, and nucleic acids. However, most previous molecules were developed as single molecular systems, neglecting the concentration quenching or aggregation-caused quenching (ACQ) effect in living cell systems: conventional hydrophobic fluorophores with large πconjugated structures inherently assemble in aqueous solutions, turning off their emission and resulting in weak turnon signals as fluorogenic probes. Indeed, in many cases, IAC/IBC measurements were conducted in organic solvents where molecular aggregation can be prevented. To achieve ultrahigh IAC/IBC in conditions that resemble cellular systems, it is desirable to develop fluorogenic systems in aggregate states.