Solid-State Thermochromism Studied by Variable-Temperature Diffuse Reflectance Spectroscopy. A New Perspective on the Chromism of Salicylideneanilines

Fujiwara, Toshikatsu; Harada, Jun; Ogawa, K.

doi:10.1021/jp037438g

Cited by 114 publications

(105 citation statements)

References 27 publications

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“…This causes the orange color of 1£. The absorption tails observed in 1¢ and 1£ may indicate that not only the major portion of the enol form but also the minor portion of the cis-keto form co-exists in the crystal as suggested by Fujiwara et al 8 The red color appearing in 1¡ and 1¢ gradually faded when the crystals were kept in the dark at room temperature. The color of 1¡ returned to the original after 60 min, whereas only a slight change was observed for 1¢ after 60 min.…”

Section: Resultsmentioning

confidence: 86%

“…8 In order to compare the structure of the photo colored species of 1¡ with that of 2, the two produced trans-keto forms around an inversion center are shown in Figure 9. The NÍH group of the imine group is surrounded by the methyl groups of the tert-butyl group of the neighboring molecule.…”

Section: õ1mentioning

confidence: 99%

“…They also proposed the direct change from enol to trans-keto form from the spectral change, although the structural confirmation was obscure. 8 Harada et al reported the fluorescence spectra in the solidstate thermochromism of salicylidene aniline. 9 The above results clearly show why photochromism occurs in the crystal.…”

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confidence: 99%

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Elongated Lifetime of Unstable Colored Species by Intermolecular Hydrogen Bond Formation in Photochromic Crystals

Johmoto

Sekine

Uekusa

et al. 2009

Bulletin of the Chemical Society of Japan

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The crystallization of N-3,5-di-tert-butylsalicylidene-3-carboxyaniline (1) from a methanol solution gave three crystal forms, 1¡, 1¢, and 1£. The colorless 1¡ and pale yellow 1¢ turned red when they were irradiated with UV light whereas orange 1£ showed no color change. The lifetimes of the colored crystals were estimated to be 17 and 780 min at room temperature for 1¡ and 1¢, respectively, from IR spectra. The structure of the colored 1¡ crystal was analyzed by X-ray at 93 K. In addition to the original enol form of 1, the trans-keto form appeared on the difference electron density map with an occupancy factor of 0.117(2). This indicates that the color change was caused by the structural change from the enol to trans-keto form, which is the same as the color change previously reported in the crystal of N-3,5-di-tertbutylsalicylidene-3-nitroaniline (2) (lifetime, 1200 min). It was made clear from the structures of the trans-keto forms in the crystals of 1¡, 1¢, and 2 that the lifetime of the unstable colored form should be determined by the possibility and the strength of the intermolecular hydrogen bond formation of the NÍH group of the trans-keto form to the neighboring molecules.Light-induced reversible color change of substances is known as photochromism and organic photochromic compounds have attracted much attention over the past decades for their applications in optic data storage, electronic display systems, optical switching devices, ophthalmic glasses, and so on.1 N-Salicylideneanilines, which are the condensation products of salicylaldehydes and anilines, exhibit photochromism both in solution and in the solid state.2 Photochromic salicylideneanilines are usually pale yellow and exist in the enol form in crystals. It was proposed from spectroscopic data that the hydrogen atom of the hydroxy group is translocated to the imine nitrogen atom on irradiation with ultraviolet light. A subsequent geometrical rearrangement in the excited state is assumed to form a red photoproduct. The deep red color can be erased by irradiation with visible light or by thermal fading in the dark. Although many studies have been carried out over three decades, there remains a controversy about the structure of the colored species.3 In a previous paper, we analyzed directly the structure of the photoinduced colored species of N-3,5-di-tert-butylsalicylidene-3-nitroaniline (2) by X-ray using two-photon excitation, which was the first crystallographic determination of structural change showing reversible photochromism in organic crystals. 4 This crystal was selected because the photoproduct has the longest lifetime among a variety of salicylideneaniline crystals. 5 The molecular structure before irradiation takes the enol form. The pale yellow crystal turned dark red when it was irradiated with laser light of 730 nm, twice the wavelength of the absorption maximum at 365 nm at room temperature. After the laser irradiation, the crystal structure was determined by X-ray diffraction analysis. The difference electron density map sho...

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Section: Resultsmentioning

confidence: 86%

Section: õ1mentioning

confidence: 99%

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Elongated Lifetime of Unstable Colored Species by Intermolecular Hydrogen Bond Formation in Photochromic Crystals

Johmoto

Sekine

Uekusa

et al. 2009

Bulletin of the Chemical Society of Japan

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“…16,17 It is generally accepted that the stable form of the SA molecule is an enol form with an intramolecular hydrogen bond between the hydroxyl proton and the nitrogen atom. It was only recently demonstrated 18 that the ground state is colorless instead of pale yellow as believed until now. In 1964, Cohen et al 3 showed that the presence of an ortho-hydroxy group is a structural requirement for the photochromism of these compounds.…”

Section: Introductionmentioning

confidence: 99%

Polymorphism inN-Salicylideneaniline Reconsidered

Arod

Pattison

Schenk

et al. 2007

Crystal Growth & Design

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ABSTRACT:The aromatic Schiff base N-salicylideneaniline (SA) represents the aristotype of a whole family of chromic derivatives. SA forms two photochromic polymorphs, R 1 and R 2 , both of which feature non-coplanar phenyl rings. Since many details of its reversible photoreactivity are still unexplained, we report the structure of a planar, thermochromic polymorph, named , and propose a new model for the structure of the R 1 -polymorph. Finally, we discuss structure-property relations between the polymorphs and the to R 1 phase transition.

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“…In this particular study, although the SP functionalised 2 μm diameter microbeads appeared coloured when in the MC form, the high degree of light scattering inhibits transmittance measurements. Surface reflection spectroscopy is an alternative powerful instrument to study dyes and colours and it has been used for a wide range of applications such as determining chromic behaviour of thermochromic organic compounds in crystalline powders 13 , measuring physically adsorbed colorimetric reagents on polystyrene beads for solid phase extractions 14 , developing fibre optic sensors based on the immobilisation of a coloured chelating agent on a cellulose membrane 15 , reflection studies on the surface of spiropyran monolayers for detection of the formation of aggregates from the merocyanine form 16 and pigment detection on biological samples 17 18 19 20 21 . These functionalised beads therefore should exhibit switchable binding of certain ions, which could have interesting potential for photo-controlled retention and release of bound species.…”

Section: Introductionmentioning

confidence: 99%

Polystyrene bead-based system for optical sensing using spiropyran photoswitches

Scarmagnani¹,

Walsh²,

Slater³

et al. 2008

J. Mater. Chem.

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Spiropyran derivatives have been immobilised on the surface of polystyrene microbeads using different immobilisation strategies. These functionalised polymeric beads can be reversibly switched between the colourless inactive spiropyran (SP) and highly coloured (purple) active merocyanine (MC) forms using low power light sources, such as light emitting diodes (LEDs). A UV-LED (375 nm) is used for the SP to MC conversion, and a white LED (430-760 nm) for the reverse MC to SP conversion. The photochromic behaviour of the coated beads has been characterised using different LEDs and reflection spectroscopy, employing optic fibres and an in-house designed holder. Investigations into the metal-ion binding behaviour of the spiropyran modified microbeads have shown that Cu 2+ ions cause an appreciable colour and spectral change when brought into contact with the beads in the MC form, suggesting that a significant interaction is occurring. However, the Cu 2+ ions can be completely expelled by photonicconversion of the beads into the inactive SP form using a white LED. This sequence has been successfully repeated six times suggesting that it is possible to cycle through activation of the functionalised beads from a non-binding to a binding form (SP to MC) using a UV-LED, allow binding with Cu 2+ ions to occur, and subsequently, expel the bound ions and regenerate the passive SP surface using a white-LED. Other metals, such as calcium, do not cause any appreciable colour or spectral change over the same concentration range and in the presence of the same anion (final concentration 7.1 x 10 -4 M nitrate salt in ethanol). The system is therefore self-indicating in terms of whether the active MC or inactive SP forms are present, and whether Cu 2+ ions are bound to the MC form. In principle, therefore, these functionalised beads could form the basis of a photoswitchable stationary phase for metal ion binding and detection: irradiation of the stationary phase with UV-LEDs causes retention of guest species due to the presence of the MC form, while subsequent exposure to white LEDs causes release of guest species into the mobile phase.

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Solid-State Thermochromism Studied by Variable-Temperature Diffuse Reflectance Spectroscopy. A New Perspective on the Chromism of Salicylideneanilines

Cited by 114 publications

References 27 publications

Elongated Lifetime of Unstable Colored Species by Intermolecular Hydrogen Bond Formation in Photochromic Crystals

Elongated Lifetime of Unstable Colored Species by Intermolecular Hydrogen Bond Formation in Photochromic Crystals

Polymorphism inN-Salicylideneaniline Reconsidered

Polystyrene bead-based system for optical sensing using spiropyran photoswitches

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