Synthesis, Characterization, and Photochromic Studies of Cyclometalated Iridium(III) Complexes Containing a Spironaphthoxazine Moiety

A series of cyclometalated iridium­(III)
complexes has been designed
and synthesized, and their photophysical, photochromic, and electrochemical
properties have been studied. The X-ray crystal structure of complex 2 has been determined. The emission properties of the complexes
have been shown to be readily perturbed through the modification of
the electronic properties of the phenylpyridine ligand. With different
substituents at the phenylpyridine ligand of iridium­(III) complexes
of 1 (−H), 2 (−OMe), 3 (−CHO), and 4 (−CF3), they can display intense 3MLCT [dπ­(Ir) →
π*­(diimine)] luminescence from 530 to 640 nm to span across
the green to orange region. The spectral assignment is also in agreement
with the electrochemical studies and DFT calculations. In addition,
the photochromic behavior can be easily modulated by varying the substituents
on the C∧N ligand without the need for tedious modification
of the spirooxazine framework. By analyzing the kinetic profiles of
backward bleaching reactions, less electron-rich iridium­(III) complexes
can stabilize the merocyanine form with a higher activation barrier.
The studies have provided not only fundamental understanding on structure–property
relationships that govern the versatile luminescence behavior of these
Ir­(III) complexes but also the guiding principles in the molecular
design for the future developments of visible light-driven photoswitches.