Photochromic Dithienylethene-Containing Boron(III) Ketoiminates: Modulation of Photo-Responsive Behavior through Variation of Intramolecular Motion

A series of dithienylethene-containing boron(III) ketoiminates, as well as their corresponding beta-ketoimine ligands, have been synthesized and characterized. The photophysical, electrochemical, and photochromic properties of the compounds have been studied. Photocyclization has been found to be suppressed upon introduction of a phenyl substituent on the nitrogen atom of the beta-ketoiminate core, whereas photochromism could be observed by replacement of the phenyl substituent with a bulky mesityl group. It is believed that the steric effect of the mesityl unit restricts molecular rotation, resulting in such a prominent difference in the photochromic properties.