Studies On The Design And Properties Of Stepwise Photochromic Metal Complexes With Dithienylethene

Photochromic diarylethene compounds have attracted much attention in view of their unique properties of excellent thermally stability,fatigue resistance,and fast light response.Photochromic compounds containing more than one dithienylethene(DTE)unit can achieve stepwise photochromic reactions upon irradiation with appropriate light.Nevertheless,stepwise photochromic reactions in a combined molecule with multidithienylethene units are usually inaccessible because of facile intercomponent energy transfer from ring-open DTE to adjacent ring-closed moiety that prohibits further photocyclization to attain fully ring-closed form.It is envisioned that incorporating multi-DTE ligands to a metal coordinated system is a feasible approach to achieve stepwise photochromic reaction.It is known that the five-/six-memebered rings linking two cis-oriented diaryl moieties on the diarylethene compounds are mostly organic ligands.In this paper,chelating metal complexes were first introduced into molecular switchs to serve as five-memebered ring bound to two cis-arranged dithienyl groups,which provides a new way to design and synthesize novel functional metal-organic photochromic molecules.Herein,we designed and synthesized a series of metal complexes containing diarylethene units,and the properties of stepwise photochromic reactions were studied.1.Ruthenium(?)complex DTE-C?C-Ru(dppe)2Cl(lo)containing one DTE-acetylide as well as DTE-C=C-Ru(dppe)2-C=C-DTE(2oo,3oo,4oo)with two DTE-acetylides have been prepared and characterized.The interconversions of four-states are in-situ monitored by UV-vis-NIR,NMR spectral and electrochemical studies.Complex 1o exhibited mutil-stimuli response to light irradiation and redox.Complex 3oo only converted to the partial ring-closed 3co product but not full ring-closed 3cc product,while 4oo all converted to 4cc directly without the partial ring-closed 4oo1?4co transformation.Whereas,the cyclization reaction of 2oo was not observed under the same experimental conditions.The oxidized species of 3oo+and 4oo+can also undergo photocyclization under the irradiation of UV lights,but oxidized species 2oo+can still not show photocyclization.2.A new type of photochromis switch has been accessed with cis-arranged dithienyl groups bound directly to metal-dithiolene complexes.Their photochromic proproties have been investigated by UV-vis,1H NMR and 31P NMR spectra.It is demonstrated that ring closure reaction of 5o,6o can take place under UV light although the conversion yield is low.In contrast,7oo and 8oo with dual DTE moieties did not show photocyclization upon irradiation at UV light.Nevertheless,upon exposure at UV light,7oo transformed into 8oo through the loss of one electron,affording a nine-atom and ten-electron aromatic system.It is found that 9oo dispalys stepwise photochromic reactions upon irradiation at UV light.