High Fatigue-Resistant Photoswitches Based on iridium(III)-DTE Systems.

A series of four differently substituted nonsymmetrical dithienylethene (DTE) units integrating bipyridine units and the corresponding cyclometalated iridium complexes were synthesized. All derivatives underwent typical reversible photoswitching reactions in solution and when embedded in polymer matrices. However, the fatigue resistance to multicycle switching in free ligands proved to be highly substituent dependent, with the benzothiophene and bipyridine substituted variant proving most stable. Interestingly, in all cases, fatigue resistance over many photoswitching cycles proved very high for all the iridium-containing species studied (>99% recovery in solution). Time-resolved spectroscopic studies indicate a different ring-closing reaction mechanism, passing through the 3MLCT state in the organometallic species compared to the free ligand. Additionally, an inversion of photoresponse is observed: irradiation at 390-440 nm promotes photocycloreversion in the free ligands but induces photocyclization in the iridium complexes. This contrasting behavior, combined with the associated optical changes, supports the potential of these systems for applications in information storage, data encryption, and anti-counterfeiting.