Iridium(III) bis-terpyridine complexes displaying long-lived pH sensitive luminescence

A bis-terpyridine complex of iridium(III) incorporating a pendent pyridyl group displays long-lived emission at pH 7 in air-equilibrated aqueous solution, but both the lifetime and intensity are reduced by a factor of > 8 upon protonation of the pyridyl nitrogen; structurally similar complexes with pendent phenolic groups are only weakly emissive and their ground-state absorption spectra show a new, low-energy band (lambda = 468 nm) upon deprotonation.