A photo-switchable molecular capsule: sequential photoinduced processes

The metastable trilacunary heteropolyoxomolybdate [PMo(9)O(31)(py)(3)](3−) – {PMo(9)}; py = pyridine) and the ditopic pyridyl bearing diarylethene (DAE) (C(25)H(16)N(2)F(6)S(2)) self-assemble via a facile ligand replacement methodology to yield the photo-active molecular capsule [(PMo(9)O(31))(2)(DAE)(3)](6−). The spatial arrangement and conformation of the three DAE ligands are directed by the surface chemistry of the molecular metal oxide precursor with exclusive ligation of the photo-active antiparallel rotamer to the polyoxometalate (POM) while the integrity of the assembly in solution has been verified by a suite of spectroscopic techniques. Electrocyclisation of the three DAEs occurs sequentially and has been investigated using a combination of steady-state and time-resolved spectroscopies with the discovery of a photochemical cascade whereby rapid photoinduced ring closure is followed by electron transfer from the ring-closed DAE to the POM in the latent donor–acceptor system on subsequent excitation. This interpretation is also supported by computational and detailed spectroelectrochemical analysis. Ring-closing quantum yields were also determined using a custom quantum yield determination setup (QYDS), providing insight into the impact of POM coordination on these processes.