In situ synthesis, crystallisation, and thin-film processing of single crystals of trans-[Ru(SO2)(NH3)4(H2O)][p-TolSO3]2 bearing SO2 linkage photo-isomers: towards optical device applications†
Metastable sulfur dioxide linkage photo-isomers can be generated in a family of ruthenium tetraammine-based complexes in their single-crystal form; this imparts them with attractive prospects as holographic data storage media (dark state = 0; photo-isomer state = 1). Embedding these optically encoded single crystals into thin-film technology via a polymer host should present one possible option for their ultimate device application. Crystals of trans-[Ru(SO2)(NH3)4(H2O)][p-TolSO3]2([Ru]-SO2) were incorporated into a polyvinyl alcohol (PVA) matrix, by in situ synthesis of [Ru]-SO2 from the reaction of trans-[Ru(SO2)(NH3)4Cl]Cl and p-tolunesulfonic acid (p-TA) in the PVA matrix, and an associated in situ precipitating crystallisation. Transmission electron microscopy and diffraction on the resulting drop-cast thin films identified these [Ru]-SO2 precipitates and their crystallinity; low-temperature solid-state UV-vis absorption spectroscopy confirmed that the desired SO2 photo-isomerisation in [Ru]-SO2 was uncompromised by its inclusion in thin films. The size and distribution of the embedded crystals were optimised by spin coating thin films of various in situ crystallised precipitates of [Ru]-SO2 that emanated from chemical reaction mixtures of trans-[Ru(SO2)(NH3)4Cl]Cl/p-TA/PVA. Results demonstrate the viability of the inclusion of single crystals of [Ru]-SO2 in thin films for optical device applications.