Solid-state Photochromic Properties Research Articles

Naphthalene-embedded spiropyran derivative-A type of conjugated expanded material with solid-state photochromic properties and tunable color switching range

Due to the limited free volume in the solid state, spiropyrans generally exhibit photochromic properties in solution or mixed thin films. However, few spiropyrans can display the photoisomerization process in the solid state. One conventional solution for solid-state photochromism is to embed the spiropyran on polymer chains or introduce bulky groups to create an efficient free volume in the solid state. In this article, we attempt to introduce large conjugated fragments on the spiropyran backbone to construct a donor-acceptor (D-A) building block that not only possesses an enlarged π-electron system with enhanced electronic delocalization capability but also exhibits an improved free volume for efficient solid-state photoisomerization. Through this strategy, we have successfully embedded the naphthalene ring on the spiropyran backbone to obtain a novel D-A type conjugated building block, SP-Naph, which exhibits excellent solid-state photochromic performance and reversibility. Furthermore, the D-A structure of SP-Naph significantly tuned its photochromic color-switching range to blue. Consequently, SP-Naph was successfully applied in optical printing and invisible inks. The excellent solid photochromic properties make it exhibit remarkable photochromic effects, indicating significant potential for optical printing and anti-counterfeiting applications.

Solid-state photochromic properties of indole thiosemicarbazones with aggregation-induced emission

Four indole thiosemicarbazones have solid-state photochromism and AIE properties. Based on the single crystal structure, FT-IR spectra and theoretical calculations, the structure–activity relationship and the photochromic mechanism were revealed.

Structure–property relationships in normal and mixed dithienylethenes – polyoxometalates supramolecular assemblies with fast solid-state photochromic properties

A strategy of sequential modification of organic and inorganic components gave rise to a stepwise photophysical investigation of the photochromic performances of supramolecular assemblies of polyoxometalates with normal or mixed dithienylethenes.

Solid-state photochromic properties, mechanism and electrospun membranes of (E)-2-(benzo[b]thiophen-2-ylmethylene)-N-ethylhydrazine-1-carbothioamide

Three carbothioamide derivatives with reversible P-type photochromic properties in the solid state were synthesized in a one-step reaction. Based on the single crystal structures, the FT-IR spectra and theory calculations, the proposed photochromic mechanism was the intermolecular proton transfer between the thio-keto and thio-enol tautomer. Nanofibrous membranes were prepared by electrospinning, which showed improved reversible photochromic properties in comparison of the compound itself. This work may open a new pathway for design and synthesis of the new solid-state photochromic materials with high-performance.

Solid-state photochromic behavior of pyrazolone 4-phenylthiosemicarbazones

Pyrazolone 4-phenylthiosemicarbazones show excellent solid-state photochromic properties, thermal stability and fatigue resistance upon the UV/Vis irradiation.

Fully Oxidized and Mixed-Valent Polyoxomolybdates Structured by Bisphosphonates with Pendant Pyridine Groups: Synthesis, Structure and Photochromic Properties

Hybrid organic-inorganic polyoxometalates (POMs) were synthesized in water by the reaction of a MoVI precursor with bisphosphonate ligands functionalized by pyridine groups. The fully oxidized POM [(MoVI3O8)2(O)(O3PC(O)(C3H6NH2CH2C5H4NH)PO3)2]4− has been isolated as water insoluble pure Na salt (NaMo6(Ale-4Py)2) or mixed Na/K salt (NaKMo6(Ale-4Py)2) and their structure solved using single-crystal X-ray diffraction. The mixed-valent complex [(MoV2O4)(MoVI2O6)2{O3PC(O)(C3H6N(CH2C5H4N)2(MoVIO3))PO3}2]8− was obtained as an ammonium salt (NH4Mo6(AlePy2Mo)2), in the presence of a reducing agent (hydrazine). 31P NMR spectroscopic studies in aqueous media have allowed determining the pH stability domain of NH4Mo6(AlePy2Mo)2. NaMo6(Ale-4Py)2 and NaKMo6(Ale-4Py)2 exhibit remarkable solid-state photochromic properties in ambient conditions. Under UV excitation, they develop a very fast color-change from white to deep purple and proved to be the fastest photochromic organoammonium/POM systems. The coloration kinetics has been fully quantified for both salts and is discussed in light of the hydrogen-bonding networks.

Molybdenum Bisphosphonates with Cr(III) or Mn(III) Ions

The synthesis of MoVI bisphosphonates (BPs) complexes in the presence of a heterometallic element has been studied. Two different BPs have been used, the alendronate ligand, [O3PC(C3H6NH3)(O)PO3]4− (Ale) and a new BP derivative with a pyridine ring linked to the amino group, [O3PC(C3H6NH2CH2C5H4N)(O)PO3]4− (AlePy). Three compounds have been isolated, a tetranuclear MoVI complex with CrIII ions, (NH4)5[(Mo2O6)2(O3PC(C3H6NH3)(O)PO3)2Cr]·11H2O (Mo4(Ale)2Cr), its MnIII analogue, (NH4)4.5Na0.5[(Mo2O6)2(O3PC(C3H6NH3)(O)PO3)2Mn]·9H2O (Mo4(Ale)2Mn), and a cocrystal of two polyoxomolybdates, (NH4)10Na3[(Mo2O6)2(O3PC(C3H6NH2CH2C5H4N)(O)PO3)2Cr]2[CrMo6(OH)6O18]·37H2O ([Mo4(AlePy)2Cr]2[CrMo6]). In this latter compound an Anderson-type POM [CrMo6(OH)6O18]3− is sandwiched between two tetranuclear MoVI complexes with AlePy ligands. The protonated triply bridging oxygen atoms bound to the central CrIII ion of the Anderson anion develop strong hydrogen bonding interactions with the oxygen atoms of the bisphosphonate complexes. The UV–Vis spectra confirm the coexistence in solution of both POMs. Cyclic voltammetry experiments have been performed, showing the reduction of the Mo centers. In strong contrast with the reported MoVI BP systems, the presence of trivalent cations in close proximity to the MoVI centers dramatically impact the potential solid-state photochromic properties of these compounds.

Solid‐State Photochromism of Chromenes: Enhanced Photocoloration and Observation of Unstable Colored Species at Low Temperatures

Solid-state photochromism of benzopyrans and naphthopyrans (chromenes) was investigated in the temperature range between 300 and 80 K. Variable-temperature diffuse reflectance spectroscopy of microcrystalline powders showed that the extent of photocoloration was greatly enhanced at low temperatures. All the chromenes examined exhibited solid-state photochromism at low temperatures, even when they showed little or no photocoloration at room temperature. The solid-state photochromic properties of the chromenes were quite similar to those reported for analogous photochromic compounds of spiropyrans and spirooxazines, which indicates that these classes of compounds are generally photochromic even in the solid state. Photobleaching reactions of the colored merocyanine forms proceeded at low temperatures through the formation of a colorless intermediate, instead of directly resuming the original closed form. In addition to two stable planar merocyanine forms, which are usually observed in the photochromic reactions in solution, photoreactions at low temperatures allowed us to observe unstable colored species, which were tentatively assigned as nonplanar cisoid forms, and were stabilized in the solid state at low temperatures.

Structure and solid-state photochromic properties of two new compounds with pyrazolone-ring

Two new organic photochromic compounds based on pyrazolone were synthesized and further characterized by elemental analysis, MS, IR spectra, and 1H NMR spectra. The photochromic properties and photochemical kinetics of them have been studied by UV absorption spectra under irradiation of 365 nm light. The photochromism of pyrazolone derivatives in the solid state has been so far explained only in terms of the light-induced change of absorption and their crystal structures, which is caused by the shift of the tautomeric equilibrium between the enol and keto forms. In this work, their IR spectra have been measured before and after irradiation. Based on the IR spectra and crystal structure analysis, a reasonable mechanism was proposed, the photochromic phenomenon may be due to the photoisomerization from enol-form to keto-form through proton transfer.

Solid-State Photochromic Properties and Mechanism of 1-Phenyl-3-methyl-4-(3-chlorobenzal)-5-hydroxypyrazole 4-Methylthiosemicarbazone

4-Acylhydroxypyrazoles combined with thiosemicarbazide derivants exhibit excellent photochromism in the crystalline state. Upon irradiation with 365 nm light, colorless enol-form isomers are converted to the yellow keto-form isomers. FT-IR, UV/vis, and fluorescence spectra were used to investigate the photochromic behavior of 1-phenyl-3-methyl-4-(3-chlorobenzal)-5-hydroxypyrazole 4-methylthiosemicarbazone. A possible photochromic mechanism has been proposed based on the analysis of the crystal structure of the sample.

Novel Photochromic Homopolymers Based on 1,2-Bis(3-thienyl)cyclopentenes

Incorporation of photochromic molecules into polymer matrices is necessary for materials applications such as optical information processing. Several novel homopolymers were prepared from 1,2-bis(3-thienyl)cyclopentene derivatives using ring-opening metathesis polymerization techniques. Analysis by UV−vis absorption spectroscopy revealed that, in solution, they retained the appealing photochromic behavior exhibited by their respective monomers. The polymers were cast as thin films and spin-coated onto quartz substrates where the solid-state photochromic properties of the polymers were similar to those in solution.

2-p-Cyanophenyl-1,8a-dihydroazulene-1,1-dicarbonitrile and Methyl 1-Cyano-2-p-cyanophenyl-1,8a-dihydroazulene-1-carboxylate

The title compounds, C 19 H 11 N 3 and C 20 H 14 N 2 O 2 , show solid-state photochromic properties. In both compounds, the dihydroazulene moiety was found to adopt the boat conformation.