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

Abstract

We rationalized the predominance of photoinduced electron transfer in quenching the fluorescence of tetrazine-based near-infrared fluorogenic labels.

Photoinduced Charge Centralization Quenches the Fluorescence of Conjugation-Fused Tetrazine Labels with Red-to-Near-Infrared Emissions

“…This improved planarity facilitates the integration of tetrazine into the π-conjugation system of the entire label, thereby enhancing the electronic communication between them. 31 In such a label, the main fluorophore functions as an electron donor, whereas tetrazine plays the role of electron acceptor (Scheme 1b, left). Photoexcitation activates electron transfer (ET) from the main fluorophore to the tetrazine, thus leading to fluorescence quenching.…”

“…This quenching pathway is also present in visible tetrazine labels, where EnT frequently prevails. Interestingly, another quenching pathway, i.e., photoinduced charge centralization (PCC), 31 was discovered during their investigation of conjugation-fused tetrazine labels in the visible region. In this scenario, the tetrazine fragment is fused into the whole label, forming a unified π-conjugation (Scheme 1b, right).…”

“…Liu et al. proposed two models centered on energy flow processes, − i.e., energy transfer (EnT) and internal conversion (IC), to elucidate the fluorescence quenching of tetrazine-based labels exhibiting visible fluorescence. These models involve energy transfer to a dark state (ETDS) for tetrazine-isolated labels and internal conversion to a dark state (ICDS) for tetrazine-integrated labels, , respectively.…”

“…In such circumstances, the above-mentioned EnT or IC processes become energetically unfavorable. Shen and co-workers affirmed the predominance of photoinduced induced electron transfer (PET) in quenching the fluorescence of tetrazine-isolated labels featuring deep-red and NIR emissions . In such a label, the main fluorophore functions as an electron donor, whereas tetrazine plays the role of electron acceptor (Scheme b, left).…”