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

Abstract

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.