Visible-Light-Driven On/Off Photochromism of a Polyoxometalate Diarylethene Coordination Complex

Herein we report the first photochromic polyoxometalate (POM)-based diarylethene (DAE) coordination complex, prepared by ligation of two cobalt(III)-incorporated borotungstates [(BW11O39CoIII)-W-III-O-VI](6-) with the ditopic pyridyl-containing diarylethene (C25H16N2F6S2). The solution-state composition, structure, and stability of the assembly were probed using H-1 and F-19 nuclear magnetic resonance spectroscopy (NMR), electrospray ionization quadrupolar time-of-flight mass spectrometry (ESI-QTOF-MS), ultraviolet-visible spectroscopy (UV-vis), and small angle X-ray scattering (SAXS), revealing that the complex self organizes to adopt a molecular dumbbell structure due to electrostatic and steric considerations. This conformation is a prerequisite for the photocyclization reaction. The assembly was found to be switchable between two states using visible light due to the perturbation of the DAE electronic structure on coordination to the POM. We present photophysical data, including the reaction quantum efficiency of the molecular switch in both directions measured using a custom-built quantum yield determination setup in addition to fatigue resistance on prolonged irradiation.