Influence of CB[n] Complexation on the Quenching of 2,4,6-triphenylpyrylium Excited States by Fe2+ Ions

This manuscript focuses on the influence that the addition of Fe(2+) 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). (1)H-NMR spectroscopy does not provide evidence supporting the formation of a ternary TP(+)@CB[n]-Fe(2+) complex. Emission quenching studies indicate that the prevalent deactivation mechanism for the quenching of TP(+) emission by Fe(2+) 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 Fe(2+) 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.