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 (MLCT)-M-3 [d pi(Ir) -> pi*(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 boolean AND 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.