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Red-emitting oxazine fluorophores are shown to bind to cucurbit[7]uril (CB[7]) with high affinity. Their fluorescence quantum yield and lifetime are thereby enhanced owing to shielding of the dyes from water. Using CB[7] as an imaging additive leads to a larger number of photons detected per molecule in super-resolution experiments with the dye ATTO655. [ABSTRACT FROM AUTHOR]

Although biological imaging is mostly performed in aqueous media, it is hardly ever considered that water acts as a classic fluorescence quencher for organic fluorophores. By investigating the fluorescence properties of 42 common organic fluorophores recommended for biological labelling, we demonstrate that H 2 O reduces their fluorescence quantum yield and lifetime by up to threefold and uncover the underlying fluorescence quenching mechanism. We show that the quenching efficiency is significantly larger for red-emitting probes and follows an energy gap law. The fluorescence quenching finds its origin in high-energy vibrations of the solvent (OH groups), as methanol and other linear alcohols are also found to quench the emission, whereas it is restored in deuterated solvents. Our observations are consistent with a mechanism by which the electronic excitation of the fluorophore is resonantly transferred to overtones and combination transitions of high-frequency vibrational stretching modes of the solvent through space and not through hydrogen bonds. Insight into this solvent-assisted quenching mechanism opens the door to the rational design of brighter fluorescent probes by offering a justification for protecting organic fluorophores from the solvent via encapsulation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)