Azobenzene-Appended Bis-Cyclometalated Iridium(III) Bipyridyl Complexes

A new synthetic route toward photochromic azobenzene-appended bipyridyl ligands has been developed, and 20 new cationic iridium­(III) bis-cyclometalated complexes containing up to four azobenzene fragments on their structure have been synthesized and characterized electronically and spectroscopically. These compounds incorporate photochromic azobenzene units in their neutral pyridyl ligands 1–5, and in four of them azobenzenes have been also introduced a posteriori on their phenylpyridyl ligands by palladium-catalyzed cross-coupling. UV–vis-monitored light-triggered trans-to-cis isomerization of the azobenzene-appended ligands revealed a strong inhibition of this process upon coordination to the d⁶-metal ion. TD-DTF calculations revealed that this inhibition could be a consequence of a metal to ligand charge transfer relaxation process.