Influence of CB[n] complexation on the quenching of 2,4,6-triphenylpyrylium excited states by Fe2+ ions

• Excited states of TP+@CB[n] inclusion complexes interact with Fe2+.
• No ternary TP+@CB[n] complexes with Fe2+ in aqueous solutions were observed.
• The quenching rate constants of TP+ triplet excited states decreases in CB[n].

This manuscript focuses on the influence that the addition of Fe2+ as electron donor quencher exerts on the photophysics of 2,4,6-triphenylpyrylium (TP+) depending on the formation or not of supramolecular inclusion complexes with cucurbit[n]uril (n: 7 or 8). 1H-NMR spectroscopy does not provide evidence supporting the formation of a ternary TP+@CB[n]–Fe2+ complex. Emission quenching studies indicate that the prevalent deactivation mechanism for the quenching of TP+ emission by Fe2+ is by increasing the ionic strength of the solution, with no evidence for the occurrence of dynamic quenching. Laser flash photolysis indicates that while the triplet excited state of TP+ is instantaneously quenched by Fe2+ in the absence of CB[n], formation of the TP+@CB[n] inclusion complex protects TP+ triplet excited state from quenching, an effect that is more pronounced in the case of CB[8] due to the deeper penetration and more complete encapsulation of the heterocyclic pyrylium core inside the larger CB[8] capsule.

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