Low-energy optical switching of SO 2 linkage isomerisation in single crystals of a ruthenium-based coordination complex.
Jacqueline M ColeDavid J GosztolaSven O SylvesterPublished in: RSC advances (2021)
Single crystals that behave as optical switches are desirable for a wide range of applications, from optical sensors to read-write memory media. A series of ruthenium-based complexes that exhibit optical switching in their single-crystal form via SO 2 linkage photoisomerisation are of prospective interest for these technologies. This study explores the optical switching behaviour in one such complex, trans -[Ru(SO 2 )(NH 3 ) 4 (H 2 O)]tosylate 2 (1), in terms of its dark and photoinduced crystal structure, as well as its light and thermal decay characteristics, which are deduced by photocrystallography, single-crystal optical absorption spectroscopy and microscopy. Photocrystallography results reveal that a photoisomerisation level of 21.5(5)% is achievable in 1. Biphasic photochromic crystals of 1 were generated by applying green and then red light to switch on and off the η 2 -(OS)O photoisomer in different regions of a crystal. Heat is a known alternative to its thermal decay, whereby a method is demonstrated that employs optical absorption spectra to determine its activation energy of 30 kJ mol -1 . This low-energy barrier to optical switching agrees well with computational studies on 1, as well as being comparable to activation energies in ruthenium-based nitrosyl linkage photoisomers that also display solid-state optical switching.