Photoinduced electron transfer endows fluorogenicity in tetrazine-based near-infrared labels

Tetrazine-functionalized fluorogenic labels are pivotal in various scientific domains, but their fluorogenicity often diminishes when the emission wavelength extends into the near-infrared (NIR) region. This investigation confirms that photoinduced electron transfer (PET) is the primary mechanism causing fluorescence quenching in such NIR labels. Furthermore, we have discovered an unprecedented photoinduced charge centralization (PCC) within the conjugated frameworks of tetrazine-integrated fluorogenic dyes. These insights into the mechanisms of fluorescence quenching pave the way for advancing tetrazine chemistry at the photophysical level. Subsequently, we introduce a rational molecular design approach for crafting tetrazine-based NIR labels that leverages the PET mechanism to significantly boost their fluorogenic response. We rationalized the predominance of photoinduced electron transfer in quenching the fluorescence of tetrazine-based near-infrared fluorogenic labels.