Photochromic Crystals Research Articles

Self-assembled solvato-morphologically controlled photochromic crystals

Here we describe, for the first time, intriguing solvato-morphological control of spiropyran-based microcrystalline structures. These microstructures exhibit reversible photoisomerization upon light irradiation (UV/Vis) in the solid-state. Finally, light-guided aggregation of these microstructures at the liquid/air interface is also demonstrated.

Femtosecond Electron Diffraction Study of the Cyclization Reaction in Crystalline Diarylethene

Femtosecond electron di raction is used to directly resolve the atomic mo- tions involved in the ring closing reaction induced in a photochromic single crystal. The measurements were performed using our newly developed setup capable of delivering sub-500 fs electron bunches containing 10 6 electrons per pulse. Theoretical calculations were also performed.

Recording volume holograms on color centers in a CaF2 crystal

The conditions for preparing photochromic CaF2 crystals, recording holograms with 532-nm radiation in them, and postexposure photothermal treatment of samples with holograms that provide the formation of holographic elements of significant thickness (about 1 cm) are considered. It is shown that the diffraction efficiency of volume holograms in such crystals in the case of reading out by radiation with wave-lengths of 532 and 632.8 nm can be as high as 10–15%. The role of the recording mechanism and the Borrmann effect in the fabrication of these holograms is demonstrated.

Preliminary neutron powder diffraction analysis of a meta-stable colored form in photochromic crystal usingiMATERIAin J-PARC

Preliminary neutron powder diffraction analysis of a meta-stable colored form in photochromic crystal using<i>iMATERIA</i>in J-PARC

Luminescent and photochemical processes in CdBr2 : AgCl crystals

This paper reports on the results of the investigation into the optical luminescence properties of photochromic crystals CdBr2 : AgCl grown by the Bridgman-Stockbarger method. It has been shown that, under X-ray, optical, and N2-laser excitations of the grown crystals, there occurs emission due to Ag+ impurities in addition to emission from centers characteristic of CdBr2. The photostimulated chemical reactions occurring in CdBr2 : AgCl lead to a weakening of the luminescence and to a change in its spectral composition. Models of photosensitive centers and centers of photochemical coloring have been proposed. The mechanisms of the photochromic effect have been considered. The nature of luminescent and trapping centers has been discussed.

1,4-Bis(1,3-dioxo-2-indenylidene)cyclohexane: polymorphism, gas phase oxidation and enol form mediated radical formation in the solid state

Crystallization of 1,4-bis(1,3-dioxo-2-indenylidene)cyclohexane from toluene and dichloromethane solutions afforded yellow photochromic and orange non-photochromic crystals, respectively. In situRaman spectroscopy of the photochromic form revealed the presence of an enol form. Both forms undergo sublimation assisted dehydrogenation under aerobic conditions.

Influence of silver clusters on the light absorption in CdBr2-Ag crystals

Experimental studies of the absorption spectra of CdBr2-Ag photochromic crystals revealed several absorption bands positioned close to the intrinsic absorption edge. It is suggested that impurity silver ions, neutral silver atoms and intrinsic lattice defects form nanoclusters which are responsible for the absorption peaks within the transparency range of the crystal. The effect of UV radiation on the absorption profile is also discussed in the framework of the proposed model.

A different photo-sensitivity of isostructural crystals of N-(3,5-dihalosalicylidene)-2,6-dimethylaniline analogues: search for the definite reaction room in the crystal to exhibit photochromism

Photo-sensitivity and X-ray crystal structure of three N-(3,5-dihalosalicylidene)-2,6-dimethylaniline analogues were determined to reveal a definite space maintained in the photochromic crystals.

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

Abstract The crystallization of N-3,5-di-tert-butylsalicylidene-3-carboxyaniline (1) from a methanol solution gave three crystal forms, 1α, 1β, and 1γ. The colorless 1α and pale yellow 1β turned red when they were irradiated with UV light whereas orange 1γ showed no color change. The lifetimes of the colored crystals were estimated to be 17 and 780 min at room temperature for 1α and 1β, respectively, from IR spectra. The structure of the colored 1α 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-tert-butylsalicylidene-3-nitroaniline (2) (lifetime, 1200 min). It was made clear from the structures of the trans-keto forms in the crystals of 1α, 1β, 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 N–H group of the trans-keto form to the neighboring molecules.

Photochromism of a Methyl Viologen Bismuth(III) Chloride: Structural Variation Before and After UV Irradiation

Color scheme: Reversibly photochromic crystals of (MV)Bi2Cl8 (methyl viologen, MV2+: N,N′-dimethyl-4,4′-bipyridinium) show structural variations before and after UV irradiation. Color reversion is accomplished by heating in air (see picture). ([Bi2Cl8]2−)∞ double-octahedral chains serve as electron donors to in situ generated MV2+ dications.

Energy barrier between states of a bistable center in photochromic crystals CdF2:Ga and CdF2:In

The establishment of thermal equilibrium between photoinduced (shallow) and ground (deep) states of bistable DX centers in photochromic crystals CdF2:In and CdF2:Ga, which are used as real-time holographic media, is studied based on the notions of chemical kinetics. Two mechanisms of mutual transformation of shallow and deep centers—the tunnel mechanism and the mechanism with the participation of free charge carriers—are considered. Equations describing the decay of a photoinduced shallow state are obtained. These equations take into account the distribution of electrons between the photoinduced and ground states and the conduction band. Analysis of the experimental kinetic curves of the decay of photoexcited shallow centers makes it possible to determine the activation energies and barrier height for thermally activated processes of mutual transformation of shallow and deep centers. In CdF2:In and CdF2:Ga, this barrier, which determines the decay kinetics of holograms, lies above the bottom of the conduction band by ∼10 and ∼500 meV, respectively.

Diarylethene microcrystals make directional jumps upon ultraviolet irradiation

Microcrystals of a diarylethene {1,2-bis[5'-methyl-2'-(2"-pyridyl)thiazolyl]perfluorocyclo-pentene} undergo jumps upon photoirradiation. These photochromic crystals present molecular structural changes upon irradiation with ultraviolet light because of reversible photocyclization reactions. When the energy absorbed by crystals reaches about 10 microJ, the uniaxial stress induced in the crystal lattice relaxes through directional jumps. If one prevents crystals from jumping, then parallel, equidistant cracks appear on crystal surfaces. These photomechanical effects could result from a Grinfeld surface instability.

Design, Synthesis, Structural and Nonlinear Optical Properties of Photochromic Crystals: Toward Reversible Molecular Switches

Two new anil molecules exhibiting photochromism in the crystalline state, N-(4-hydroxy)-salicylidene-amino-4-(methylbenzoate) (2) and N-(3,5-di-tert-butylsalicylidene)-4-aminopyridine (3), are obtained. Upon irradiation in the UV, the yellow crystals change color to red, owing to enol-keto intramolecular tautomerism. The red color disappears, when crystals are left in the dark or irradiated with visible light. 3 has the most stable keto form among all anil-type photochromic compounds (τ = 460 days at room temperature). Both exhibit nonlinear optical (NLO) properties and show powder second harmonic generation (SHG) of respectively 10 and 3 times vs urea. X-ray diffraction shows acentric structures where molecules line up “head-to-tail” through hydrogen bonds for 2 (space group Pc), or form a chiral helix 3 (space group P32). Evidence of reversible structural change is given for 3, and we demonstrate the functionality of this crystal as an NLO switching material, as SHG can be photomodulated by about 30%.

Photochromic Crystals: Toward an Understanding of Color Development in the Solid State

Intermolecular interactions between fluorene groups of propargylallenes define the solid state photochromic response of these materials. Examination of crystal structures of both photoresponsive and nonresponsive forms (including solvates) indicates that all compounds that are photochromic in the solid state exhibit donor/acceptor π···π interactions of fluorene aromatic systems that lead to infinite 1-D ribbons. Such interactions are absent in nonphotochromic crystalline forms.

Crystalline Photochromism of 2-Propynylallene Derivatives

Abstract Some 2-propynylallene derivatives exhibited color change from pale-yellow to green upon photoirradiation with visible light in the solid state. The green color disappeared either by heating or dissolving into solvents. The photochromism of 2-propynylallene derivatives depends largely on the substituents on the aromatic rings. Crystallographic analysis indicates that the overlap of the π systems of the fluorene moiety in the photochromic crystals allow photoinduced charge-transfer interactions in the solid-state.

Multicolor photochromism of two- and three-component diarylethene crystals.

Novel photochromic single crystals composed of three different kinds of diarylethenes, 1,2-bis(3,5-dimethyl-2-thienyl)perfluorocyclopentene (1a), 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene (2a), and 1,2-bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene (3a), have been prepared. The three-component crystals turned yellow, orange, red, purple, blue, green, or black upon irradiation with light of appropriate wavelengths. The colors of the crystals were thermally stable in the dark and completely bleached by irradiation with visible light. Such multicolored photochromic crystals have potential for the application to optoelectronic devices, such as multifrequency three-dimensional optical memory media or full-color displays.

Multi-Colored Photochromic Crystals of Diarylethene Mixtures

Multi-Colored Photochromic Crystals of Diarylethene Mixtures

結晶化学の最前線 構造と物性の予測はどこまで可能か ２ 結晶構造からみた物性予測と反応予測 結晶のフォトクロミズム

X-ray crystallographic study on photochromic crystals has been introduced. Although a number of photochromic materials have been reported, compounds which show photochromic reactivity in the crystalline phase are very rare and detailed X-ray crystallographic study on the crystalline photochromism is limited, because of the difficulty to increase the conversion rates in the crystals. Recently, in situ X-ray crystallographic analysis has been successfully carried out for N-salicylideneaniline, hexaarylbiimidazole, and diarylethene, by employing new phototechniques, such as two-photon excitation or linear-polarized light illumination. This paper reports on such direct X-ray structural analysis of diarylethenes as well as N-salicylideneanilines.

Photochromic Materials for Reversible Switching of Second Order Nonlinear Optical Properties

This paper reports on materials whose second order nonlinear optical (NLO) properties can be switched by light. We synthesized and studied the properties of a series of substituted N-salicylidene anilines which are noncentrosymmetric and photochromic crystals. All compounds exhibit second harmonic generation (SHG). One of the compounds exists in two different cristalline forms, one being photochromic and the other thermochromic. Photoswitching of SHG was performed : irradiation by UV light lead to a decrease of SHG up to 60% of the SHG signal at 1064 nm and 10% at 1907 nm.

Paramagnetic susceptibility of additively colored CdF2:In photochromic crystals

The paramagnetic susceptibility Kpara of CdF2:In crystals with metastable indium centers has been measured in darkness after photobleaching the crystals in visible light in the temperature interval 4–300 K. For crystals cooled in darkness to liquid-helium temperature Kpara is wholly determined by the accompanying impurity Mn2+ with magnetic moment J=5/2. Illumination of the crystals leads to the appearance of an induced signal δKpara due to the formation of centers with J=1/2. The results of the experiments indicate the absence of paramagnetism in the deep state of the indium center and its existence in the shallow (donor) state, i.e., they confirm the two-electron (negative-U) nature of the deep indium level in CdF2.