To understand why AIE-Tz exhibits emission quenching in the aggregate state despite the incorporation of AIEgens, we further investigated the interaction between the tetrazine moiety and AIEgens in the aggregate state. Single crystal X-ray diffraction (XRD) analysis and molecular dynamics (MD) simulations were conducted to obtain aggregate models of MBTPA-Tz, and intermolecular center-tocenter distances between the tetrazine and surrounding aryl rings were calculated. As expected, we observed proximal molecular interactions in the aggregate state: 3.6-4.7 Å from the XRD result and 3.9-4.9 Å from the MD calculation (Figure -10, S24 in Supporting Information). The single crystal structure of MBTPA-Tz reveals a tetrazine-chromophore distance as close as 3.668 Å (Figure ). This distance is comparable to or even shorter than that of reported tetrazine fluorogenic dyes known to efficiently quench emissions through energy transfer mechanisms . Therefore, this result indicates that tetrazine can enhance emission quenching efficiency upon aggregation via intermolecular interactions with AIEgens. This intermolecular quenching effect of the tetrazine unit was experimentally confirmed using a commercially available AIEgen (TPE-CN) as a fluorescence indicator (Figure ). We measured the emission intensity of 10 µM TPE-CN, co-aggregated with TPE-Tz at different concentrations. Consequently, we observed that the emission of the aggregate was apparently quenched by 50.3% with 0.1 µM TPE-Tz addition; the emission intensity dropped 94.6% and even 99.7% with 1 µM and 10 µM TPE-Tz addition, respectively (Figure ). Considering there is no direct through-bond connection between TPE-CN and TPE-Tz, this quenching effect arises from intermolecular interactions between TPE-Tz and TPE-CN directed by aggregation.