The previous photocrystallographic reports on 1 did not employ optimum light-induced experimental conditions. Before embarking on a study of these optical switching properties, though, we undertake a new photocrystallographic determination of 1 because we need to compare the optical switching behaviour of 1 with more optimal light-induced crystal structure information. This paper thus seeks to gain insights into the light-induced optical and thermal switching properties of 1. 9 However, these results are on the powdered form of 1 those of the single-crystal phase are expected to differ since the light-absorption and scattering characteristics of a material depend inherently on its form. 4 Its thermally-induced reverse isomerisation process has been tracked by multi-temperature infrared (IR) spectroscopy, yielding an activation energy, E a = 58.4 kJ mol −1. The single-crystal photochromism characteristics of 1 have also not been ascertained, despite their potential application in optical memory devices. In particular, their single-crystal optical absorption properties have not been explored, nor have the kinetics associated with the photoisomerisation process of 1.
While these distinct isomeric structures of 1 have been confirmed crystallographically, their single-crystal optical switching behaviour remains unknown. Scheme 1 Compound 1 in its dark-state configuration and its SO 2 photoisomeric configurations. Note that the dark-state η 1-SO 2 isomer remains the predominant species in 1 once photoisomerised, owing to photoconversion limits that are imposed by crystal-lattice strain. 10 Scheme 1 illustrates these photoisomerisation processes. 8–20 Photocrystallography 21–25 studies have shown that 11.1(1)% of an η 2-(OS)O photoisomer can be generated within the crystal structure of 1 at 90 K, 9 while 36% of the less thermally stable η 1-OSO photoisomer can form at 13 K, albeit split over two disordered orientations with 24% and 12% photoconversion. The coordination complex, trans-tosylate 2, ( 1) is one in a family of ruthenium sulfur-dioxide based (hereafter denoted ) materials that exhibit SO 2 linkage photoisomerisation. 6,7 The light-sensitive ligand switches from its dark-state configuration to a photoisomer upon light activation, to afford a binary encoding in the crystal. Single-crystal optical switching has been observed in a wide range of coordination complexes via the process of linkage photoisomerisation. This may lead to correlated photoswitching effects, whose ‘out-of-equilibrium’ manifestations have been coined as “the real terra nova of solid-state chemistry”. This is because such changes carry long-range effects throughout the material, given the periodic nature of a crystal-lattice environment.
Single-crystal optical switches are particularly appealing where their functional origins lie in light-induced structural changes. Optical switching in a crystalline material is particularly helpful for solid-state device technologies, as a crystal is a pure form of solid-state media as such, it can be incorporated into a device with modest fabrication or processing effort. Introduction Materials that exhibit optical switching are of great interest given their wide-ranging applications as light-driven molecular rotors, 1 photocatalysts, 2 protein nanovalves, 3 and read–write optical memory media, 4 to name just a few. 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.
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. 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. Photocrystallography results reveal that a photoisomerisation level of 21.5(5)% is achievable in 1. This study explores the optical switching behaviour in one such complex, trans-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.
#BRUKER APEX 3 SINGLE CRYSTAL VIDEO WINDOW SERIES#
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. Single crystals that behave as optical switches are desirable for a wide range of applications, from optical sensors to read–write memory media.
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