X-ray Analysis of Structural Changes in Photochromic Salicylideneaniline Crystals. Solid-State Reaction Induced by Two-Photon Excitation

Harada, Jun; Uekusa, Hidehiro; Ohashi, Yuji

doi:10.1021/ja9842969

Cited by 306 publications

(231 citation statements)

References 14 publications

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“…The same motion was also reported to be a key process in the photochromism of SAs and the photodimerization of trans-cinnamides in the crystalline state. 12,45,46 Our growth disorder (see Figure 6) is clearly different and cannot be explained by such a pedal model; it is similar to Destro et al's 14 and is also found in some other N-benzylideneanilines. 47 The molecules in this phase are nonplanar.…”

Section: Resultssupporting

confidence: 82%

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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Section: Resultssupporting

confidence: 82%

Polymorphism inN-Salicylideneaniline Reconsidered

Arod

Pattison

Schenk

et al. 2007

Crystal Growth & Design

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“…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.…”

mentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

“…However, it remains unclear why the unstable colored species of different crystals have different lifetime in photochromism. Recently Mikami and Nakamura proposed from theoretical calculations based on the structure of the trans-keto form produced in photo colored crystal 4 that the long lifetime of the colored species of 2 is due to the intermolecular hydrogen bond, which is formed between the photo-produced trans-keto form and the nitro group of the neighboring molecule. 10 However, no experimental support has been observed yet.…”

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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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“…Analysis of the electron density difference map (Figure 3c) showed only small changes indicating that there was likely much less than 10% photoconversion within the crystal. 14 The polarized absorption spectra before and after irradiation (Figure 3d) illustrate the dramatic changes in the absorption spectra that occur upon photoisomerization. These results demonstrate that crystalline SO materials could be used as filter materials and possibly as data storage media where the differences in absorption could correspond to the 1's and 0's of the binary computer language.…”

Section: Photochromic Materialsmentioning

confidence: 99%