Investigating the Properties of Triangle Terthiophene and Triphenylamine Configured Propeller-like Photochromic Dye with Ethyne Bridge

Synthesis-oriented design led us to the construction of a propeller-like dye, containing the triangle terthiophene and triphenylamine units. It reveals typical photochromic properties with alternated UV (390 nm) and visible light (˃ 440 nm) irradiation and the dye solution (in THF) color was also toggled between yellow-green and colorless. A new absorption band was observed in visible region (415-600 nm). Additionally, the photochromic dye was highly emissive with the absolute quantum yield being 0.27. After UV light irradiation, the emission was quenched significantly (Φ = 0.08) at photo-stationary state, and thus establishing a switchable emission "on-off" system by alternated UV/visible light irradiation cycle. Detailed structural analysis was carried out based on the optimized dye structure. Both the antiparallel conformation and the distance of reactive carbon atoms (< 4.2 Å) led to the smoothly photochromic behavior.

Investigating the Properties of Double Triangle Terthiophene Configured Dumbbell-Like Photochromic Dye with Ethyne and 1,3-Butadiene Bridge

Dumbbell-like photochromic dyes were constructed by incorporation of double triangle terthiophene with ethyne or 1,3-butadiene bridge. Regular photochromic behavior was investigated with alternated UV (365 nm) and Visible light (˃ 400 nm) irradiation. However, the different bridge group leads to distinct difference in their photochromic wavelength. For the ethyne bridged triangle terthiophene (DT1), the photochromic wavelength was observed around 500-700 nm (peak value: 605 nm) and the solution turned to red with 365 nm light irradiation. However, the photochromic wavelength was blue shift to 418-550 nm and the solution was turned to light yellow for 1,3-butadiene bridged dye (DT2). Both of the colored solution can be bleached via visible light irradiation. Additionally, the two dyes in THF were emissive with absolute quantum yield (QY) of 0.36/0.40. Along with the photo-induced photocyclization process, the emissive solution can be effectively quenched at photo-stationary sate (Φ = 0.05/0.04). And emission "on-off" cycle could be established based on the UV/visible light irradiation cycle.

Photo-induced 6π-electrocyclisation and cycloreversion of isolated dithienylethene anions

The diarylethene chromophore is commonly used in light-triggered molecular switches. The chromophore undergoes reversible 6π-electrocyclisation (ring closing) and cycloreversion (ring opening) reactions upon exposure to UV and visible light, respectively, providing bidirectional photoswitching. Here, we investigate the gas-phase photoisomerisation of meta- (m) and para- (p) substituted dithienylethene carboxylate anions (DTE^-) using tandem ion mobility mass spectrometry coupled with laser excitation. The ring-closed forms of p-DTE^- and m-DTE^- are found to undergo cycloreversion in the gas phase with maximum responses associated with bands in the visible (λ_max ≈ 600 nm) and the ultraviolet (λ_max ≈ 360 nm). The ring-open p-DTE^- isomer undergoes 6π-electrocyclisation in the ultraviolet region at wavelengths shorter than 350 nm, whereas no evidence is found for the corresponding electrocyclisation of ring-open m-DTE^-, a situation attributed to the fact that the antiparallel geometry required for electrocyclisation of m-DTE^- is energetically disfavoured. This highlights the influence of the carboxylate substitution position on the photochemical properties of DTE molecules. We find no evidence for the formation in the gas phase of the undesirable cyclic byproduct, which causes fatigue of DTE photoswitches in solution.

Spectroscopic Tracking of Salicylideneaniline Photocolored Crystals: An Attempt to Quantify Polymorph-Dependent Features toward Precise Structure-Function Correlation Analysis

Three polymorphs of salicylideneaniline (SA) were prepared, and their photochromic behavior was examined using a recently developed single-crystal microscopic UV-vis spectroscopy approach. This system enabled us to acquire absorption data during the bleaching process as a function of temperature and visible light intensity. First, we demonstrated that, in contrast to the generally accepted assumption, the bleaching curves were notably influenced by the degree of photosaturation at the initial stage. By modifying our kinetic model to include the term representing the initial degree of photosaturation, we successfully obtained the kinetic parameters intrinsic to each crystal structure. Second, we further analyzed the kinetic parameters to show that the bleaching process was accelerated by visible light irradiation to a significantly higher degree than by thermal relaxation. The two bleaching-prompting effects were quantitatively compared between two photochromic polymorphs, α₁ and α₂; the long life of the photoproduct in α₂ was attributed to efficient self-shielding from visible light irradiation enabled by its structural features. These results prompted us to reexamine the simple dualistic photochemical and thermal classification of photochromic systems and will provide a foundation for the precise structure-function analysis of crystalline materials, including SAs.

Crystal structure and photochromism of 1-(2,5-dimethyl-3-thienyl)-2-[2-methyl-5-(benzaldoxime)-3-thienyl] perfluorocyclopentene, C23H17F6NOS2

C23H17F6NOS2, triclinic, P1̄ (no. 2), a = 8.379(3) Å, b = 11.509(2) Å, c = 12.817(3) Å, α = 71.272(3)°, β = 81.342(4)°, γ = 77.553(3)°, V = 1138.7(5) Å3, Z = 2, R gt(F) = 0.0489, wR ref(F 2) = 0.1296, T = 296(2) K.

Two [Ln4] molecular rings folded as compact tetrahedra

A new highly photo-switchable ligand furnishes supramolecular tetrahedral nanomagnets with Ln(iii) ions (Ln = Dy, Tb). Intramolecular weak interactions define the conformation of the ligand, quenching the photochromic activity.

Electro-activity and magnetic switching in lanthanide-based single-molecule magnets

The present work reviews switching of single-molecule magnetic behaviour achieved through various stimuli such as temperature, light irradiation, redox processes, solvation/desolvation, and magnetic field.

Structure and photochromism of 1-[2-methyl-5-phenyl-3-thienyl]-2-[2-methyl-5-(4-chlorophenyl)-3-thienyl]3,3,4,4,5,5-hexafluorocyclopent-1-ene, C27H16ClF6S2

C27H16ClF6S2, monclinic, P21/c (no. 14), a = 24.1193(5) Å, b = 9.2419(2) Å, c = 10.8343(2) Å, β = 96.1260(10)°, V = 2401.26(8) Å3, Z = 4, Rgt(F) = 0.0292, wRref(F2) = 0.0878, T = 100(2) K.

Solid-state one-way photoisomerisation of Z,E,Z-1,6-(4,4'-diphenyl)hexa-1,3,5-triene dicarboxylate examined using higher-order derivative spectra and powder XRD patterns

Higher order derivative spectra were applied at first to one-way ZEZ-to-EEE photoisomerisation of dimethyl ester (ZEZ-DPH1) of the titled compound in a methylcyclohexane solution. Many common crossing points emerged in UV-induced derivative-spectral changes to reveal the direct ZEZ-to-EEE photoisomerisation without the transient formation of an intermediate to suggest the bicycle-pedal mechanism. The solid-state photoisomerisation was subsequently monitored by tracing changes in the fourth-order derivatives of absorption spectra of a thin crystalline layer of ZEZ-DPH1 prepared by the drop-casting method, because the distortion of absorption spectra due to light scattering is cancelled. It was suggested that the solid-state photochemical event consists of three steps: fast ZEZ-to-EEE photoisomerisation, a subsequent slow ZEZ-to-EEE photoisomerisation and very slow disappearance of the EEE-isomer. Studies on powder XRD were also carried out for a drop-cast solid layer of ZEZ-DPH1 to disclose the coexistence of a crystal form other than the original one, and the former exhibited faster ZEZ-to-EEE photoisomerisation when compared with the original crystal form. The results revealed by XRD analysis are in line with those obtained by higher-order derivative spectra, confirming the solid-state one-way photoisomerisation to take place through the bicycle-pedal process.

The crystal structure of 1,2-bis[2-methyl-5-(3-cyanophenyl)-3-thienyl]-3,3,4,4,5,5-hexafluoro-cyclopent-1-ene, C29H16F6N2S2

C29H16F6N2S2, monoclinic, C2/c, a = 18.910(3) Å, b = 8.5720(14) Å, c = 16.757(3) Å, β = 100.474(2)°, V = 2670.9(7) Å3, Z = 4, R gt(F) = 0.0825 , wR ref(F 2) = 0.1833 , T = 296(2) K.

Photo-activation of Single Molecule Magnet Behavior in a Manganese-based Complex

A major roadblock to fully realizing molecular electronic devices is the ability to control the properties of each molecule in the device. Herein we report the control of the magnetic properties of single-molecule magnets (SMMs), which can be used in memory devices, by using a photo-isomerizable diarthylenthene ligand. Photo-isomerization of the diarylethene ligand bridging two manganese salen complexes with visible light caused a significant change in the SMM behavior due to opening of the six-membered ring of diarylethene ligand, accompanied by reorganization of the entire molecule. The ring-opening activated the frequency-dependent magnetization of the complex. Our results are a major step towards the realization of molecular memory devices composed of SMMs because the SMM behaviour can be turned on and off simply by irradiating the molecule.

Crystal structure of photochromic 1-(2-methyl-5-phenyl-3-thienyl-2-[2-methyl-5-(4-ethoxylphenyl)-3-thienyl] 3,3,4,4,5,5-hexafluoro-cyclopent-1-ene, C29H22F6OS2

C29H22F6OS2, monoclinic, P21/c, a = 6.4504(2) Å, b = 16.9752(4) Å, c = 22.8762(6) Å, β = 91.7790(10)°, V = 2503.66(12) Å3, Z = 4, R gt (F) = 0.0377, wR ref (F 2 ) = 0.1156, T = 100(2) K.

Discovery and development of photochromic diarylethenes

A new family of thermally irreversible photochromic molecules, named “diarylethene,” was serendipitously discovered a quarter of a century ago. The diarylethenes undergo thermally irreversible, fatigue resistant, ultrafast and highly sensitive photochromic reactions. Many of diarylethenes can undergo photochromic reactions even in the single-crystalline phase. The outstanding photochromic performance attracts considerable attention from both scientific and technological points of view, and stimulates research from fundamental physico-chemical aspects to various applications. Here, it is reported how such thermally irreversible photochromic diarylethenes were discovered and developed.

New insights into the by-product fatigue mechanism of the photo-induced ring-opening in diarylethenes

The photochromic properties of diarylethenes, some of the most studied class of molecular switches, are known to be controlled by non-adiabatic decay at a conical intersection seam. Nevertheless, as their fatigue-reaction mechanism - leading to non-photochromic products - is yet to be understood, we investigate the photo-chemical formation of the so-called by-product isomer using three complementary computational methods (MMVB, CASSCF and CASPT2) on three model systems of increasing complexity. We show that for the ring-opening reaction a transition state on S1(2A) involving bond breaking of the penta-ring leads to a low energy S1(2A)/S0(1A) conical intersection seam, which lies above one of the transition states leading to the by-product isomer on the ground state. Therefore, radiationless decay and subsequent side-product formation can take place explaining the photo-degradation responsible for the by-product generation in diarylethene-type molecules. The effect of dynamic electron correlation and the possible role of inter-system crossing along the penta-ring opening coordinate are discussed as well.

Photo-control of the magnetic properties of Dy(iii) and Ho(iii) homometal coordination polymers bridged by a diarylethene ligand

Two-dimensional Dy(iii) and Ho(iii) homometal coordination polymers containing the DTE ligand were obtained, and the magnetic properties of the open and closed forms were investigated.

Photochromism in sound-induced alignment of a diarylethene supramolecular nanofibre

A photochromic supramolecular nanofibre, composed of a diarylethene derivative, exhibits hydrodynamic alignment upon exposure to the audible sound.

Spontaneous formation of photochromic coatings made of reversible microfibrils and nanofibrils on an elastomer substrate

We report the spontaneous formation of photochromic microcrystalline and nanocrystalline fibrils forming dense coatings of cactuslike supramolecular structures on the surface of a soft poly(dimethylsiloxane) (PDMS) elastomer. The initial deposition of the photochromic molecules of diarylethenes on the elastomer is done by dip adsorption, a process that permits the homogeneous distribution of the molecules not only on the surface but also in the inner part of the polymer. Detailed thermal and microscopy studies reveal that the growth process of the fibrils is initiated by the formation of crystal seeds of the diarylethene in the proximity of the elastomer's surface empty voids and progresses toward the elastomer-air interface as a result of the high mobility of the molecules at room temperature. Fibril formation is possible only when the molecules are in the open form because the UV irradiation responsible for their transformation to the close isomeric form immediately after deposition totally prohibits the crystals' formation. Furthermore, the UV irradiation of the grown supramolecular assemblies provokes their destruction, but when the irradiated samples are left to recover under ambient conditions, they form new assemblies of fibrils in a faster and more efficient way. The resulting systems exhibit superhydrophobic to slightly hydrophobic properties with differences of almost 80° in water contact angles upon dark storage-UV irradiation cycles. The proposed systems can be an alternative to the facile formation of reversible photochromic fibrils on soft polymer surfaces for utilization on diverse soft devices, where controlled surface morphology and wettability are desired.

Competitive direct vs. indirect photochromism dynamics of constrained inverse dithienylethene molecules

Relaxation observed through several parallel pathways from the first excited state to the ground-state in inverse dithienylethene molecules.

Adsorption-induced stability reversal of photochromic diarylethene on metal surfaces

A scanning tunneling microscopy study of a photochromic diarylethene adsorbed on Au and Cu reveals the reversal of thermodynamic stability between its two isomers compared to the gas phase, in solution, and its single crystal, which could result from the molecule-substrate interaction such as charge transfer and hybridization.

Crystal structure of 1-[2-n-butyl-5-formyl-3-thienyl]-2-[2-cyano-1,5- dimethyl-4-pyrryl]-3,3,4,4,5,5-hexafluoro-cyclopent-1-ene, C21H18F6N2OS

C21H18F6N2OS, monoclinic, P21/c (no. 14), a = 9.331(1) Å, b = 20.492(2) Å, c = 11.998(1) Å, β = 108.748(1)°, V = 2172.4 Å3, Z = 4, Rgt(F) = 0.0710, wRref(F2) = 0.2198, T = 296 K.

Crystal structure of 1-[5-(3,4-difluorophenyl)-2-methylthiophen-3-yl]-2- (2-cyano-1,5-dimethyl-1H-pyrrol-4-yl) -3,3,4,4,5,5-hexafluoro-cyclopent- 1-ene, C23H14F8N2S

C23H14F8N2S, triclinic, P1¯ (no. 2), a = 8.701(2) Å, b = 11.881(2) Å, c = 12.342(3) Å, α = 64.932(3)°, β = 71.913(3)°, γ = 86.599(3)°, V = 1094.7 Å3, Z = 2, Rgt(F) = 0.0425, wRref(F2) = 0.1244, T = 294 K.