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Nitroprusside ion in its three structural isomers. GS: thermally stable ground state; SI, SII: light-induced metastable states. The arrows indicate the light-induced isomerization pathways and the corresponding wavelengths for SNP.
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![Figure 4. Scheme of the light-induced isomerization for [Ru(bpy) 2 OSO]...](publication/258684278/figure/fig4/AS:669951698403358@1536740340854/Scheme-of-the-light-induced-isomerization-for-Rubpy-2-OSO-from-its-ground-state-GS_Q320.jpg)
V.D.); seicke@uos.de (S.E.); kspringf@uos.de (K.S.) Abstract: We have successfully proposed the application of transition metal compounds in holographic recording media. Such compounds feature an ultra-fast light-induced linkage isomerization of the transition-metal–ligand bond with switching times in the sub-picosecond regime and lifetimes from mi...
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Context 1
... structural ground state of nitroprusside compounds [ML 5 NO] m± , with M being the central transition metal, L ligands and m± the overall charge, is depicted in Figure 3 with [Fe(CN) 5 )NO] 2− as an example. Its photofunctionality is located at the Fe-N-O bond. ...
Context 2
... is possible by exposure of SNP to light in the blue-green spectral range (350-580 nm). Remarkably, the system allows for complete optically induced backswitching in the red and near-infrared spectral range [30] as depicted by the specific wavelengths given in Figure 3 despite the possibility of a thermal relaxation from SI, SII to GS [2,7,24,31]. The activation energies for the thermal decay of SI and SII have been determined to E A,I = 0.68 eV and E A,II = 0.52 eV for SNP, respectively, resulting in lifetimes of τ I = 154 µs and τ II = 0.18 µs at room temperature and of τ > 10 15 s at nitrogen temperatures [7,32,33]. ...
Context 3
... are very small molecules (13 atoms for sodium nitroprusside (SNP), see Figure 3), and thus, the substitution of one single atom has major consequences to all features like absorption spectra, sensitivity, lifetime, etc. The spectral sensitivity for the isomerization pathways for SNP are reported to be shifted by more than 200 nm to the red (λ GS = 714 nm) in [Pt(NH 3 ) 4 Cl(NO)]·Cl 2 [59]. ...
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Citations
... [Fe II (CN) 5 -(g 2 -NO)] (meta-stable state 2: MS2), which show a relatively high stability at low temperature (<150 K), about 10 7 s at 80 K. These states can also be excited at room temperature in the solid state [164] and in solution [165], as have revealed studies using transient IR spectroscopy, but rapidly decay to the GS or the NO + ligand is liberated resulting the formation of pentacyanoferrates [165,166] whether it is fast enough to compete with the other deactivation processes [165]. ...
... The crystal structure corresponding to these states in sodium nitroprusside was solved from XRD data recorded at low temperatures [142,144]. In solid state, the lifetime for the meta-stable states is in the order of 10 15 sec at 77 K and about ms at room temperature [164]. In solution, the lifetimes are even shorter, of about 100 ps for sodium nitroprusside [165]. ...
This review summarizes the state of the art on the structural features, thermal and environmental stability, physical properties and potential applications of transition metal nitroprussides, for their 3D, 2D, 1D and 0D structures. The nitroprusside ion, [Fe(CN)5NO]²⁻, forms insoluble solids with monovalent and divalent transition metals. The crystal structure for the coordination polymers obtained with divalent metals shows a marked dependence on the used preparative route, metal nature and hydration degree, which was the origin of many incongruities in studies published a few decades ago. Nowadays, the structural features and related properties for the immense majority of the solids formed with such metal ions are known and discussed in this review. The preparation of transition metal nitroprussides using co-ligands with different coordination capability to modulate the dimensionality and related properties of the resulting solids has been on the spotlight of research during the last few years, particularly those related to atypical magnetic behavior. This subject is also herein summarized, revealing the large diversity of hybrid inorganic–organic frameworks that can be obtained with some of their physical properties only recently revealed, among them, the thermal-induced spin transition in ferrous nitroprussides containing monodentate and bridging organic ligands acting as pillar or pseudo-pillars in 2D and 3D hybrid materials. This contribution also includes a general overview of the use of spectroscopic tools such as XPS, XAS, Mössbauer, UV–vis-NIR, IR and Raman, to access electronic and structural characteristics of this family of materials. We also carried out a critical analysis of those research areas that, in our opinion, require further studies, representing opportunities to make important scientific contributions on new knowledge on this family of materials. This is the first general review on transition metal nitroprussides.
... 12 The main disadvantage of the studied compounds with respect to their applications is the stability of the generated metastable states, in which the thermal stability does not exceed 260 K. On the other hand, ruthenium sulfoxide derivatives look more suitable for photorefractive applications due to longer lifetimes of metastable states; however the compounds show a lower refractive index. 15,16 The mole-cular design of photoswitchable molecules plays a crucial role in the properties of the resulting photorefracting materials, and the understanding of the principles of the thermal stability of linkage isomers in similar systems can be extended to the whole family of photoswitchable ligands. ...
The new complexes trans-(H3O)[RuNO(NH3)4F](NO3)1.5F1.5∙0.5H2O (I) and trans-[RuNO(NH3)4F](ClO4)Cl (II) are synthesized and characterized by the single crystal X-ray diffraction. The complexes are crystallized in centrosymmetric space groups I4/m and P21/n due to specific intermolecular interactions, the strongest are represented by the N-H∙∙∙O contacts. The irradiation of the complexes in the blue-light range induces the formation of the Ru-ON isomers (MS1), determined by the IR-spectroscopy and Differential Scanning Calorimetry (DSC). The subsequent excitation of the MS1 by the infrared light induces the appearance of the Ru-(η2-(NO)) (MS2) isomers verified by the same techniques. Using combined IR and DSC analysis, the activation barriers (Ea) and frequency factors (lgk0) of the MS1→GS and MS2→GS reactions are determined. According to the kinetic parameters, the calculated lifetimes (k-1) of the MS1 at 300 K are 33 and 178 min for I and II respectively. To our best knowledge, the thermal stability of the MS1 in II is the highest among known related complexes. The thermal stability of the MS2 was found to be lower (the lifetimes are 0.12 and 0.02 s at 300 K for I and II respectively), which is characteristic for these states. The high thermal stability of the MS1 can be applied for design of the photochromic materials, as well as generally facilitate the investigation of the states.
... The nitrogen monoxide (NO) is a bioactive molecule involved in the regulation of diverse physiological processes such as germination, metabolism, cell death, opening and closing of stomata, and root growth (Misra et al., 2010). The NO can be generated through the chemical breakdown of NO donor molecules, such as SNP, with the chemical formula of Na 2 [Fe(CN) 5 NO] (Dieckmann et al., 2012;Neill et al., 2003). The SNP releases NO molecule upon light irradiation (Floryszak-Wieczorek et al., 2006). ...
... The approach to use photoswitchable molecular compounds as photofunctional building blocks in holographic materials goes back to the original proposal of Woike et al. [1][2][3]. The molecular level potentially enables a number of important features within the same material: (i) a high tuning ability of the spectral sensitivity due to targeted substitution of ligands and/or central atoms, (ii) the possibility for enabling a reversible write-read-erase cycle, (iii) a ultra-high (holographic) spatial resolution down to the molecular level, (iv) a cheap and quick synthesis on (v) a large scale, (vi) a good mechanical flexibility, (vii) the possibility for tailored dimensioning, (viii) the possibility for adapting the optical density via concentration optimization, and (ix) the possibility to record with either continuous wave (cw) or fs-laser light pulses [4]. ...
... Still, however, holographic media based on photoswitchable compounds are not available commercially. The reasons are manifold and include large costs for laborious molecular crystal growth, large optical damping by fundamental absorption, toxicity, and/or the requirement for liquid-nitrogen temperatures [4]. ...
... Our previous reports have already addressed the unique features of photofunctionality at room temperature [9,10]. Furthermore, we were able to demonstrate the possibility for embedding ruthenium sulfoxides compounds in a polymer matrix with conserved photochromic response [4]. Based on these pre-investigations, the ability to record elementary gratings with promising features for consumer-market holographic applications was proposed [11]. ...
Holographic silicon polymer films based on photoswitchable molecules are studied with respect to their performance for hologram recording, with photoswitchable ruthenium sulfoxide complexes as an example. Our systematic study reveals that it is possible to record elementary holographic lossy gratings with outstanding quality with respect to their dynamics and in- and off-Bragg read-out features. Furthermore, the possibility for the recording of multiple holograms within the same volume element via angular multiplexing as well as the recording with continuous-wave and a fs-laser pulse train is successfully demonstrated. At the same time, a strong limitation of the maximum diffraction efficiency in the order of ∼ 10⁻³ is found that cannot be counterbalanced by either the tuning of material (thickness, concentration, ...) or recording parameters (repetition rate, wavelength, ...). This limitation – being severe for any type of holographic applications – is discussed and compared with the performance of high-efficient single-crystalline reference holographic media. We conclude that the potential of sulfoxide compounds may be hidden in holography until it becomes possible to synthesize polymer films with appropriate three-dimensional structural arrangement of the photoswitchable compounds.
... The synthesis of multifunctional molecular compounds based on transition metal complexes has been extensively developed in the last decades [1][2][3][4][5][6][7]. The combination of different building blocks in one molecule or in one crystal lattice allows control of the property (magnetic, spectral etc) of one fragment influencing another sensor fragment through irradiation, temperature, pH. ...
... The importance of linkage isomerization has been highlighted in a number of reviews (8,10,11). A good understanding of the various modes of binding of an ambidentate ligand, and factors that influence these modes of binding will provide more insight in the kind of chemistry they present. ...
Abstract The binding of small molecules to metals often imparts varied chemistry to the small molecules. Such chemistry is dependent on the coordination mode of the small molecule ligands, as the coordination mode affects the electronic distributions along the ligand atoms. In this review, we outline the current knowledge of the linkage isomerization of NOx ligands in their metal complexes for both non-porphyrin and porphyrin systems. We present their modes of preparation and detection and speculate on the consequences of such linkage isomerization on the resultant chemistry.
... A second example is molecular holographic media built from transition-metal-compounds. Here, the targeted design of hologram recording materials related to a broad range of parameters including photosensitivity, spectral sensitivity and hologram lifetime has been demonstrated [5,6]. ...
Holographic spectroscopy is highlighted as a powerful tool for the analysis of photosensitive materials with pronounced alterations of the complex permittivity over a broad range in the visible spectrum, due to the advances made both in the fields of advanced holographic media and highly tunable lasers systems. To analytically discuss consequences for in- and off-Bragg reconstruction, we revised Kogelnik’s coupled wave theory strictly on the basis of complex permittivities. We extended it to comply with modern experimental parameters such as out-of-phase mixed holograms and highly modulated gratings. A spatially modulated, wavelength-dependent permittivity that superimposes a spatially homogeneous wavelength-dependent ground state spectrum is taken into account for signal wave reconstruction with bulky elementary mixed gratings as an example. The dispersion characteristics of the respective diffraction efficiency is modelled for color-center-absorption and absorption of strongly localized carriers. As an example for the theoretical possibilities of our newly derived set of equations, we present a quantitative analysis of the Borrmann effect connected to out-of-phase gratings, providing easier and more intuitive methods for the derivation of their grating parameters.
The optical bandgap (Eg) of transition metal nitroprussides remains practically undocumented, probably because these materials are usually considered wide bandgap solids, characterized by a strong metal-ligand charge-transfer band below 500 nm. In this contribution, we are reporting experimental and DFT computed data for both, 3D and 2D phases of Zn and Cd nitroprussides to get physical insight into the metal and structure effect on the optical bandgap (Eg) of these materials. 3D Ag nitroprusside, an analog solid for which the Eg value has been reported, was included for comparison. Eg values were obtained from both, UV–vis–NIR spectra and DFT calculations. The solids under study show a direct bandgap with diverse Urbach tails, which was ascribed to the presence of structural defects. Metal to ligand charge transfer within nitroprusside ion dominates the electronic structure in the valence-gap-conduction region for the 3D systems. Both, the outer metal, and the incorporation of 1-Methyl-2-pyrrolidone as an organic pillar molecule between adjacent layers for the 2D analogs, influence the electronic structure and consequently, the Eg values obtained. In these materials, the polarizing power of outer metal has a relevant role in the observed Eg value.
Four new Ru(II) complexes, [Ru(tpy)(L)(CH3CN]+, where tpy = 2,2′:6′,2″‐terpyridine and L represents a series of acetylacetonate‐based ligands, were synthesized for enhanced photoinduced ligand release with red light, λirr = 655 nm. The metal‐to‐ligand charge transfer, 1MLCT, transitions of these complexes are red‐shifted and exhibit quantum yields of ligand dissociation that are 5‐ to 7‐fold greater than that of [Ru(tpy)(bpy)(CH3CN)]2+ (bpy = 2,2'‐bipyridine) despite the absence of additional steric distortion. This series of complexes represents a new scaffold for drug photocaging and represent one of the first examples of Ru(II) photocages that can be released with light in the photodynamic therapy (PDT) window required for optimal tissue penetration.
Silica xerogels are versatile host materials for the inclusion of molecules, clusters, or nano-objects yielding host-guest compounds with unique physical, chemical or biological properties. The knowledge of the structural organization of the guest within the host is crucial for the understanding of its properties. Total scattering methods, based on Debye function analysis (DFA) and Pair Distribution Function (PDF), have become powerful tools for structural characterization of nanostructured hybrid materials. The aim of this work is to use the X-ray total scattering method to obtain structural information on photoactive molecules embedded into amorphous silica hosts with different pore sizes, to correlate their structure with the optical properties, and to explore the limitations of the chosen method. Two different photoactive complexes have been investigated. In the first example, the combined PDF and NMR study on Na2[Fe(CN)5NO].2H2O (SNP) embedded into silica matrices allows to extract the nature of the inserted species: quasi-free isolated molecules can be distinguished from nanoparticles and in the former case a model for the arrangement of cation-anion can be proposed from the PDF analysis. In the second example, a luminescent Nd3+ complex, the PDF and DFA analysis reveal that the structural organization of the embedded Nd3+ complexes is different from that of the crystalline material. Furthermore, the Nd3+ cations change the coordination from 8 to 9 during the wet-impregnation doping and adopt very similar structural arrangement as in aqueous solution, which is in agreement with the observed change in the luminescence properties
