The dark side of cyclooctatetraene (COT): Photophysics in the singlet states of “self-healing” dyes

Cyclooctatetraene (COT) attachment to fluorophores ("self-healing" dyes) is known for quenching reactive triplet states via triplet-state energy transfer (TET), enhancing photostability. However, COT's impact on singlet states remains unclear. Quantum calculations reveal that COT induces energy transfer to dark states in deep blue dyes while promoting photoinduced electron transfer (PET) and intersystem crossing (ISC) in visible dyes, potentially compromising brightness and/or photostability. To address this, we propose the use of ΔE descriptor to optimize COT's effects. Our findings uncover COT's multifaceted impact. These insights will guide the development of superior triplet state quenchers and photostable dyes.