Modelling the luminescence of iridium cyclometalated complexes encapsulated in cucurbituril.

Iridium(iii) cyclometalated complexes in aqueous solution often display relatively weak luminescence. It has been shown in previous work that this emission can be significantly enhanced (by up to two orders of magnitude) by encapsulation in cucurbit[10]uril (Q[10]). Luminescence lifetime measurements suggest a dynamic self-quenching mechanism is active, possibly due to displacement of an excited guest complex via collision with an unbound complex. We devise a model for the association of a group of iridium(iii) cyclometalated complexes with Q[10]. The model parameters are then fitted to steady-state emission titration curves. The excellent agreement of experimental data with the model provides valuable mechanistic information relating to the way this class of metal complexes interact and associate with the Q[10] host.

Iridium Cyclometalated Complexes in Host-Guest Chemistry: A Strategy for Maximizing Quantum Yield in Aqueous Media.

The weaker emission typically seen for iridium(III) cyclometalated complexes in aqueous medium can be reversed via encapsulation in cucurbit[10]uril (Q[10]). The Q[10] cavity is shown to effectively maximize quantum yields for the complexes, compared to any other medium. This may provide significant advantages for a number of sensor applications. NMR studies show that the complexes are accommodated similarly within the host molecule, even with cationic substituents attached to the ppy ligands, indicating that the hydrophobic effect is the dominant driving force for binding. Cavity-encapsulated 1:1 host-guest species dominate the emission, but 1:2 species are also indicated, which also give some enhancement of intensity. Results demonstrate that the enhancement is due primarily to much lower rates of nonradiative decay but also suggest that the encapsulation can cause a change in character of the emitting state.

Strong enhancement of luminescence from an iridium polypyridyl complex via encapsulation in cucurbituril.

An exceptional, temperature-dependent enhancement of luminescence is reported upon encapsulation of an iridium(III) polypyridyl complex in cucurbit[10]uril (Q[10]). This is the first demonstrated example of a luminescent transition metal complex occupying the Q[10] cavity with this type of differential response.