Signalling anion binding

The luminescent emission of Ru (bpy)3 is also very useful for signalling anion binding. In the emission spectra of 37-40 both a blue shift (of up to 16 nm for 40) and an increase in intensity of the Amax of the MLCT emission band was observed on addition of dihydrogenphosphate. It has been proposed that the conformational flexibility of the receptors is decreased by complexation of the anion guest thus reducing the rate of non-radiative decay through vibrational and rotational relaxation. Similarly, macrocyclic complexes 41-44 and 77-79 were also found to sense chloride by luminescence enhancement. 

SIGNALLING REVERSIBLE ANION BINDING IN AQUEOUS MEDIA... 

The angular and distance information provided by the lanthanide induced shift has found widespread application from the determination of solution structures of Ln chelates [18,19] to gaining structural information on proteins, nucleotides and amino acids [19], More recently anion binding to coordinatively unsaturated lanthanide complexes has been effectively signalled as the observed lanthanide induced shift has been directly correlated to the nature of the donor atom in the axial position [8,20,21], It is the polarisability of the axial donor that ranks the second order crystal field coefficient, B02, and hence determines the magnitude of the observed shift. Values of the mean shift of the four most-shifted axial protons of the 12-Nq ring for [Yb.la]3+ are collated in Table 2. 

Camiolo, S., Gale, P. A., Hursthouse, M. B., Light, M. E. (2003) Nitrophenyl derivatives of pyrrole 2,5-diamides structural behaviour, anion binding and colour change signalled deprotonation, Org. Biomol. Chem. 1. 4, 741-744. 

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