Cis Isomerization Research Articles

Photoresponsive, amide-based derivative of embonic acid for anion recognition

The synthesis and ion-binding properties of amide-based derivative of embonic acid and p-aminoazobenzene were described. The new compound was characterized by X-ray structural analysis and spectroscopic methods. Ligand interacts in acetonitrile with Y-shaped anions (benzoates and acetates) and dihydrogen phosphates forming complexes of 1:1 stoichiometry. In more polar DMSO the complexes stoichiometry changes to 2:1 (L:anion). Light-induced trans to cis isomerization was studied. The effect of anions on thermal back isomerization was investigated.

New electroactive and photosensitive polyamide/ternary LDH nanocomposite containing triphenylamine moieties in its backbone: synthesis and characterization

The new ternary (Mg–Zn–Al–) layered double hydroxide (LDH) with an organic modifier-containing azo group (LDH–SHDBS) as a guest anion was prepared by a co-precipitation through one-step synthetic method. The novel electroactive polyamide (EPA) was successfully prepared by direct polycondensation reaction of azelaic acid with a new synthetic diamine 4. The structure of diamine 4 was confirmed by FTIR and 1H NMR spectra. Also, polyamide/ternary LDH nanocomposites were prepared by resulting EPA and modified ternary LDH under ambient condition. The resulting data using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) showed ternary LDH were successfully distributed into the EPA matrix. Thermal behavior of the EPA and its nanocomposites were studied by thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG). The presence of LDH layers into EPA matrix improved thermal stability (T5, T10, char yield) in both air and nitrogen atmospheres. Also, photoisomerization and electrochemical behaviors of EPA and resulting nanocomposites were measured using UV–Vis spectroscopy and cyclic voltammetry (CV), respectively. The UV–Vis spectrum of the obtained nanocomposites showed two peaks at λmax = 422 and 480 nm related to π–π∗ and n–π∗ transitions of trans azobenzene. Moreover, trans to cis isomerization of azomoieties was studied by irradiation of the nanocomposites under 254 nm photons. The CV pattern of EPA exhibited a reversible anodic peak around 0.84 V, corresponding to the nitrogen atom of triphenylamine unit into polymer backbone that improved by incorporation of LDH–SHDBS into EPA matrix.

Multiresponse Kinetic Modeling of Heat-Induced Equilibrium of β-Carotene cis-trans Isomerization in Medium-Chain Triglyceride Oil.

The kinetics and mechanism of the stepwise cis-trans isomerization reactions of all-trans-β-carotene dissolved in MCT (medium-chain triglyceride) oil at temperatures in the range of 80-160 °C have been analyzed using multiresponse modeling. Quantitation of the cis-isomers was performed using HPLC-DAD and quantitation at the reaction isosbestic point at 421 nm. Multiresponse kinetic modeling using the Bayesian criterion was initially performed at 120 °C to determine the best model. Subsequently, the reparametrized Arrhenius equation was used to calculate the activation energies of all reactions. The equilibrium constants for the individual isomerization reactions were determined from the rate constants and the final product distributions. The enthalpies and entropies of the isomerization reactions were determined from the temperature dependence of the equilibrium constants. The 13-cis and 13,13'-di-cis isomers were found to be the fastest formed isomers followed by the 9-cis, 9,13-di-cis, and 13,15-di-cis isomers, where the latter was found to be formed from 13-cis and not the 15-cis isomer. The relative free energies of the β-carotene isomers were determined as all-trans < 13-cis < 9-cis < 13,13'-di-cis < 9,13-di-cis ≈ 15-cis < 13,15-di-cis. The entropic contribution of each reaction was found to play an important role in the ordering. It is concluded that the β-carotene system is quite labile at temperatures ranging from 80 to 160 °C and resulting in equilibrium distributions of the cis-trans isomers.

7-Azaindole-3-carboxylic acid and its Pt(II) and Pd(II) complexes: Crystal structure of the ligand, vibrational spectra, DFT calculations and in vitro antiproliferative activity

The crystal and molecular structure of 7-azaindole-3-carboxylic acid (7AI3CAH2) has been determined by a single-crystal X-ray diffraction analysis (space group Pca21, a = 14.247(3), b = 5.1983(10), c = 9.871(2) Å, V = 731.0(2) Å3, Z = 4). The crystal structure consists of chains of the 7AI3CAH2 molecules, arranged into ribbons and connected via intermolecular O–H⋯N and N–H⋯O hydrogen bonds. The IR and Raman spectra of 7AI3CAH2 and its deuterated derivative were recorded in the solid state. The DFT calculations at the B3LYP/6–311++G(d,p) level were performed for four conformers of the 7AI3CAH2 monomer as well as for the dimer and trimer, which included intermolecular H-bonding motifs. The analogous calculations were carried out for the deuterated derivative (7AI3CAD2). The optimized structural parameters and the calculated vibrational spectra of trimer reproduce the experiment very well. In addition, new complexes of 7AI3CAH2 with Pt(II) and Pd(II) were prepared and studied by infrared and Raman spectroscopy. The geometry optimizations and vibrational frequency calculations were conducted for two possible (cis and trans) isomers of [MCl2(7AI3CAH2)2] (where M = Pt(II) or Pd(II)) using the B3LYP method with the 6–311++G(d,p)/LanL2DZ basis sets. The combined experimental and theoretical vibrational spectroscopic studies have shown that in the solid state the platinum(II) complex exists as the cis isomer (cis-[PtCl2(7AI3CAH2)2]), whereas the palladium(II) complex has the trans conformation (trans-[PdCl2(7AI3CAH2)2]). In both isomers, two pyridine nitrogen atoms of the 7AI3CAH2 ligands and two chloride ligands are coordinated to the central Pt(II) or Pd(II) atoms in a square-planar arrangement. The carboxylic and NH groups of 7AI3CAH2 are not bonded by metal ions. Detailed vibrational assignments for 7AI3CAH2 and its Pt(II) and Pd(II) complexes have been made on the basis of the calculated potential energy distributions (PEDs). The in vitro antiproliferative activities of cis-[PtCl2(7AI3CAH2)2] and trans-[PdCl2(7AI3CAH2)2] were studied on two human cancer cell lines (T47D and A549). As follows from the obtained IC50 values, the trans-[PdCl2(7AI3CAH2)2] complex exhibits cytotoxicity against T47D cell line, which is comparable to that of cisplatin.

DFT study of formation and properties of dinuclear zirconocene cations: Effects of ligand structure, solvent, and metal on the dimerization process

Density functional theory calculations were performed to determine the stability and properties of the formation of dinuclear zirconocene cation [(Cp2ZrMe)2(μ-Me)]+, a species formed during metallocene/cocatalyst (e.g., B(C6F5)3 or MAO) activated polymerization. To improve the catalytic system by minimizing catalyst dimerization, knowledge on the geometric and electronic properties of the process is required. Here, a series of metallocene catalysts were analyzed as a function of their ligand structures, solvent and metal. Two different isomers (cis and trans) of the dimer were considered. The results show that in general the dimer structure in trans form is more stable than in the cis form. Changing ligand structures tend to destabilize the dimerization process, which is influenced by the steric hindrance on the ligand. The stability of the dimer structure is greatly affected by the choice of solvent polarity, i.e., the more polar solvent the less stability of the dimer. Substitution of Zr into Hf also shows the same trend with a more stable dimer. Vibrational frequencies were calculated for the dimers and the changes in frequencies of the Zr-(μ-Me) stretching vibration were found to correlate well with the dimerization energies (R2 = 0.88). Our study might facilitate future catalyst design in metallocene-mediated cationic polymerization.

Entangled Azobenzene‐Containing Polymers with Photoinduced Reversible Solid‐to‐Liquid Transitions for Healable and Reprocessable Photoactuators

AbstractPhotoactuators based on liquid crystal elastomers or networks are smart materials that show photoinduced motions. However, their crosslinked networks make their repair or reprocessing difficult. Here, a healable and reprocessable photoactuator is fabricated using entangled high‐molecular‐weight azobenzene‐containing polymers (azopolymers) that are non‐crosslinked. A series of linear liquid crystal azopolymers with different molecular weights are synthesized. The low‐molecular‐weight azopolymers (5–53 kg mol−1) cannot form freestanding photoactuators because their polymer chains lack entanglements, which makes them hard and brittle. In contrast, flexible and stretchable actuators are fabricated using high‐molecular‐weight azopolymers (80–100 kg mol−1) that exhibit good processability because of the polymer chain entanglements. The azopolymer photoactuators show photoinduced bending based on photoinduced trans–cis isomerization of the azopolymers on the irradiated side. The experiments show not only photoinduced phase transitions or changes in the order parameters but also photoinduced solid‐to‐liquid transition of the azopolymers resulting in shape changes and mechanical responses. Thus, photoinduced solid‐to‐liquid transition is a new mechanism for the design of photoactuators. Moreover, the azopolymer photoactuators are healable and reprocessable via solution processing or light irradiation. Healability and reprocessability prolong lifetimes of photoactuators are important for materials reusage and recycling, and represent a new strategy for the preparation of smart materials.

Recording Polarization Holograms in Polymer Films with Azo Dyes and Azo Polymers

Based on polymers with the addition of azo dyes as chromophores and azopolymers with the same covalently linked chromophores, recording media for polarization holography are created and their properties are studied when recording holograms of a plane wave front with parallel and perpendicular polarization of recording rays. It is found that the diffraction efficiency and the storage time of holograms are much longer in recording media with films of azo polymers in comparison with polymeric solid solutions of azo dyes. In the latter case, the energy of light is spent only for the trans–cis isomerization of azo dye molecules during exposure of holograms and the polymer chains do not undergo deformation with the formation of a surface relief in the polymer film. Therefore, it is preferable to use recording media based on solid solutions of azo dyes in dynamic polarization holography.

Effect of an external electric field on the dynamics and intramolecular structures of ions in an ionic liquid

Simulations of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in an external electric field have been performed using a Drude particle polarizable force field. The structure of the ions has been analyzed, with close attention paid to the configurations of the ions. The "charge arm" concept is used to explain certain changes of these configurations that would be difficult to rationalize otherwise, e.g., trans → cis isomerization of the bis(trifluoromethylsulfonyl)imide anion and extension of the alkyl chain of the cation. It has also been shown that the ions orient themselves so that their charge arms align with and stretch out along the field, and these effects occur at lower external electric field strengths than cause a change in the inherent diffusion of the ions. The dynamics of the system parallel and perpendicular to the field were analyzed, and it was found that the applied field affected the diffusion normal to the field. This is explained as a secondary effect of a change in the ion cage formed by the surrounding counterions of a given ion in the ionic liquid. The breakdown of the ion cages was rationalized by correlating changes to the inherent diffusion of the ions with other changes to the diffusion and bulk structure of the liquid, as well as considering the average forces on the ions compared to the force the ions would be expected to experience in an electric field. Parallel to the field, a drift was observed at every electric field studied. In electric fields with no changes to the ion cage structure, the relationship between the drift and electric field was found to be linear, becoming nonlinear as the ion cage structure breaks down.

An NIR-light-responsive surface molecularly imprinted polymer for photoregulated drug release in aqueous solution through porcine tissue.

The application of photoresponsive surface molecularly imprinted polymers based on azobenzene is limited by the UV light source required and their poor water solubility. Reducing the phototoxicity and solvent toxicity of the polymers therefore presents a challenge. In this work, an NIR-light-responsive surface molecularly imprinted polymer was fabricated by atom transfer radical polymerization using up-conversion nanoparticles as the core, a hydrophilic green-light-responsive azobenzene derivative as the functional monomer, and a drug as the template. The up-conversion nanoparticles core emitted green fluorescence in the range of 520-550 nm upon NIR irradiation (980 nm, 5 W cm-2), which was absorbed by the azobenzene containing molecularly imprinted polymers layer on the up-conversion nanoparticles surface. This caused the azobenzene chromophores to undergo trans→cis isomerization in phosphate buffered solution (pH = 7.4), thus resulting in NIR-light-induced drug release. The up-conversion fluorescence spectra were used to study the interaction mechanism between the azobenzene monomer and NIR light. Compared with structural analogues of the template (antifebrin and phenacetin), the NIR-light-responsive surface molecularly imprinted polymer showed excellent specificity of recognition for the template drug (paracetamol). The maximum adsorption capacity of the NIR-light-responsive surface molecularly imprinted polymer for loading of paracetamol was 16.80 μmol g-1. The NIR-light-responsive surface molecularly imprinted polymer was applied for NIR-light-induced paracetamol release in phosphate buffered solution (pH = 7.4) through porcine tissue. This work demonstrates the potential of drug delivery systems based on molecularly imprinted polymers for application in deep tissue delivery.

Synthesis and Photodynamics of Stilbenyl‐Azopyrroles: Two‐Photon Controllable Photoswitching Systems

AbstractThree new stilbenyl‐azopyrroles 3 a–c were synthesized through a Mizoroki‐Heck C−C‐type coupling reaction between the 2‐(4′‐iodophenyl‐azo)‐N‐methyl pyrrole (1), and three different para‐substituted styrene derivatives. Inclusion of additional NO2 and NMe2 groups at the para‐position of the stilbenyl section resulted in significant changes of their linear and non‐linear optical properties. The photoisomerization behavior was studied through ultrafast laser techniques for single‐ and two‐photon excitation. The time‐resolved studies indicate that, despite the drastic changes in conjugation, the typical path for photoisomerization is maintained in these systems for both single and biphotonic excitation. In particular, the NO2 substituted molecule showed improved two‐photon absorption capacities, together with a significant trans−cis isomerization channel, implying that the photoswitching process can be controlled with high spatial precision through non‐linear optical excitation.

Quantitative analyses of optically induced birefringence in azo dye containing polymers

We study the steady-state and dynamics of photo-orientation of photoisomerizable azo dyes in films of polymers by using the Kerr gate optical setup, and we show to what extent such experiments can be used to quantify the dyes photoisomerization and photo-orientation. We report on results at different film thicknesses and absorbances and irradiation light intensities. We rationalize the double exponential growth used to describe empirically the onset of photo-induced birefringence in azo-polymers by using the theory of photo-orientation, and we give analytical expressions for the reaction rates, demonstrating a good agreement with experiments, and we show how to extract the trans → cis isomerization quantum yield from birefringence data. We believe that this work will lead to broader studies of the effect of the environment of complex materials on optically reactive molecules.

Updatable colorful display of vector hologram in azo–poly(9‐vinylcarbazole)–TiO2 nanocomposite films

ABSTRACTReversible photoconversion can realize multiple utilizations of optical materials, which is essential for updatable display. Azopolymer has the ability of reversible photoconversion benefiting from its recycled trans–cis isomerization. Commonly, introduction of inorganic nanoparticles can improve the optical response rate and holographic reconstruction efficiency of azopolymer. However, aggregation of inorganic nanoparticles in azopolymers is unavoidable, not only aggravating light scattering but also reducing film homogeneity and chemical activity. It is difficult to realize reversible optical conversion in the photochromic material. Here, we use poly(9‐vinylcarbazole) (PVK) and porous TiO2 to improve optical properties of azopolymer. The spatial dispersion ability of the photosensitive units is increased greatly. Diffraction efficiency of vector‐holographic gratings in the organic–inorganic comodulated film is eight times higher than that without PVK. Erasing ratio of the stored hologram reaches 97.8%. Based on such property, updatable vector hologram reconstruction with different colors lights is realized. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48537.

COSY catalyses trans–cis isomerization and lactonization in the biosynthesis of coumarins

Coumarins, also known as 1,2-benzopyrones, comprise a large class of secondary metabolites that are ubiquitously found throughout the plant kingdom. In many plant species, coumarins are particularly important for iron acquisition and plant defence. Here, we show that COUMARIN SYNTHASE (COSY) is a key enzyme in the biosynthesis of coumarins. Arabidopsis thaliana cosy mutants have strongly reduced levels of coumarin and accumulate o-hydroxyphenylpropanoids instead. Accordingly, cosy mutants have reduced iron content and show growth defects when grown under conditions in which there is a limited availability of iron. Recombinant COSY is able to produce umbelliferone, esculetin and scopoletin from their respective o-hydroxycinnamoyl-CoA thioesters by two reaction steps-a trans-cis isomerization followed by a lactonization. This conversion happens partially spontaneously and is catalysed by light, which explains why the need for an enzyme for this conversion has been overlooked. The combined results show that COSY has an essential function in the biosynthesis of coumarins in organs that are shielded from light, such as roots. These findings provide routes to improving coumarin production in crops or by microbial fermentation.

Inhibition of Rho GTPases in Invertebrate Growth Cones Induces a Switch in Responsiveness to Retinoic Acid.

During development, growth cones are essential for axon pathfinding by sensing numerous guidance cues in their environment. Retinoic acid, the metabolite of vitamin A, is important for neurite outgrowth during vertebrate development, but may also play a role in axon guidance, though little is known of the cellular mechanisms involved. Our previous studies showed that retinoid-induced growth cone turning of invertebrate motorneurons requires local protein synthesis and calcium influx. However, the signalling pathways that link calcium influx to cytoskeletal dynamics involved in retinoid-mediated growth cone turning are not currently known. The Rho GTPases, Cdc42 and Rac, are known regulators of the growth cone cytoskeleton. Here, we demonstrated that inhibition of Cdc42 or Rac not only prevented growth cone turning toward retinoic acid but could also induce a switch in growth cone responsiveness to chemorepulsion or growth cone collapse. However, the effects of Cdc42 or Rac inhibition on growth cone responsiveness differed, depending on whether the turning was induced by the all-trans or 9-cis retinoid isomer. The effects also differed depending on whether the growth cones maintained communication with the cell body. These data strongly suggest that Cdc42 and Rac are downstream effectors of retinoic acid during growth cone guidance.

Full and fragmented permutationally invariant polynomial potential energy surfaces for trans and cis N-methyl acetamide and isomerization saddle points.

We report full and fragmented potential energy surfaces (PESs) for N-methyl acetamide that contain the cis and trans isomers and the saddle points separating them. The full PES uses Permutationally Invariant Polynomials (PIPs) in reduced symmetry which describe the three-fold symmetry of each methyl rotor. A more efficient PES is an extension of the fragmented PIP approach we reported recently. In this approach, the set of Morse variables is partitioned and the fragmented PIP basis is the union of the PIP basis for each set of variables. This approach is general and can be used with neural network fits. The fits are done using roughly 250 000 electronic energies and gradients obtained from direct dynamics, using the B3LYP/cc-pVDZ level of theory. The full PIP basis in 66 Morse variables, with a maximum polynomial order of 3, contains 8040 linear coefficients. The fragmented PIP basis, also with a maximum polynomial order of 3, contains 6121 coefficients. The root-mean-square errors of both PESs are roughly 100 cm-1 for energies and 15 cm-1/bohr per atom for gradients, for energies up to roughly 45 000 cm-1, relative to the trans minimum. Energies and normal mode frequencies of the cis and trans isomers for the full and fragmented PESs agree well with direct calculations. The energies of the two saddle points separating these minima are precisely given by both PESs. Diffusion Monte Carlo calculations of the zero-point energies of the two isomers are also reported.

Room Temperature Reversible Z→E Photoisomerization of Azobenzene Appended to Anthraquinone‐Benzimidazole Based Photoswitches with Resolved n→π* Absorption Band

Light‐triggered substituted azobenzene‐based molecular switches are well known for their potential applications as molecular machines. The Z‐isomer stability affected by heteroaromatic groups, extended aromaticity, different substituents, and varying the solvents based on their polarity. In this regards, five different anthraquinone/imidazole‐based azobenzene derivatives have been synthesized with different electronic push/pull substituents. The detailed study of photoswitching processes with kinetic data was appraised by using UV/Vis and 1H‐NMR spectroscopic techniques. The investigation of light‐induced hydroxyl group conversion to quinone‐hydrazone tautomerization has been observed during the isomerization. Most importantly, intermolecular hydrogen bonding interaction between tautomeric form and a higher polar solvent (DMSO) block the isomerization, but in a less polar solvent (DCM), light‐induced trans ↔ cis isomerization takes place by tautomerization pathway with well‐separated π→π* and n→π* transitions. Further, the detailed mechanistic study of solvent‐assisted light‐induced tautomerization with the role of hydrogen bonding and the following WRITE‐READ‐ERASE‐READ system have been derived by using molecular logic gates.

Influences of Ortho‐Fluoroazobenzenes on Liquid Crystalline Phase Stability and 2D (Planar) Actuation Properties of Liquid Crystalline Elastomers

AbstractIn this article, the influences of ortho‐fluoroazobenzenes (o‐Fbs) on liquid crystalline (LC) phase stability and actuation properties of liquid crystalline elastomers (LCEs) are presented. Such o‐Fbs find interest because they allow full photoswitching with visible light (no ultraviolet (UV) radiation). Novel o‐Fb monomers and crosslinkers are synthesized and characterized. Different amounts of an LC mixture are replaced with synthesized o‐Fbs successively and their influences on the LC phase stability in the cis and trans forms are observed through measuring the related clearing temperatures via polarized optical microscopy. LCE precursors containing 0, 1, 3, 5, 7, and 10 mol% o‐Fb monomer or crosslinker are aligned in a magnetic field and polymerized as films in the LC phase. Thermal and visible light–controlled photochemical 2D (planar) actuation properties of LCE samples are investigated and compared to LCEs containing a liquid crystalline non‐fluorinated azobenzene monomer as reference. It is shown that, while the favorable photochemistry is obtained, the integration of o‐Fbs is less effective for photoswitching of the LC phase, because i) less o‐Fbs can be integrated without destroying the LC phase and ii) the trans–cis isomerization is less effective in destroying the LC phase.

Synthesis, mesogenic and photoisomerization studies of (E)-4-[(4-pentyloxyphenyl)diazenyl]phenyl alkanoates

ABSTRACTHomologous series of esters of (E)-4-[(4-pentyloxyphenyl)diazenyl]phenol and aliphatic carboxylic acids were synthesized, 5O-m for short. Derivatives with alkyl chains longer than seven carbon atoms are described in this article for the first time. The mesogenic properties and phase transition parameters (temperatures and enthalpies) were measured using a polarizing microscopy and a differential scanning calorimetry. Investigated compounds exhibit occurrence of the enantiotropic nematic phase, despite two derivatives with the longest alkyl chains. One can observe two crystalline phases in two derivatives (5O-6, 5O-7). The presence of the azo group in the homologous series of compounds suggests that the possibility of trans–cis isomerization is controlled by light. Such studies have been carried out and their results suggest that the presence of two trans–cis isomerization mechanisms described as the first-order reaction.

Rapid relaxation pathway of the excited state of linear merocyanines in solutions

AbstractExcited‐state relaxation of linear merocyanine dyes in solution is investigated using time‐resolved spectroscopy techniques and quantum chemical calculations. The merocyanine L‐Mero4 and phenyl‐substituted P‐L‐Mero4 have a S‐trans and S‐cis structure, respectively, consisting of indole moiety as the donor, indandione as the acceptor, and the tetramethine as the bridge. The time‐correlated single‐photon counting (TCSPC) picosecond measurements after excitation at wavelength 515 nm to the ππ* state yield emission curves with a short component τ1 in the range of 27–160 ps and a second component τ2 of 200–780 ps for L‐Mero4. In P‐L‐Mero4, τ1 lies in the range of 18–150 ps and τ2 220–520 ps. The subfemtosecond transient absorption measurements yield a short component around 0.4–1.4 ps, and the second/third components are similar to those in the TCPSC measurements. The analysis of the experimental data demonstrates that the ground state recovery exhibits a biexponential rise and rapidly indicates that the conversion back to the electronic ground state provides a fast, nonradiative pathway. Quantum chemical calculations on the electronic structures and their dependence on the molecular confirmation are performed. We identify the excited states and the relaxation path along the twist of the center double bonds in tetramethine that might be the nonradiative pathway. The C=C double bond is weakened in the ππ* state. The phenyl substitution in the conjugated double bond weakens this C=C bond, lowers the isomerization barrier, increases the nonradiative rate, and reduces the emission quantum yield. In polar solvents, the energy of the perpendicular conformer along the trans–cis isomerization path is increased to achieve less coupling to the ground state surface. Because of the small barrier to the trans form, these two conformers establish an equilibrium condition. The trans form, which lies at a lower energy, gains more population and thus has a higher emission yield.

An azobenzene container showing a definite folding - synthesis and structural investigation.

The combination of photo-switchable units with macrocycles is a very interesting field in supramolecular chemistry. Here, we present the synthesis of a foldable container consisting of two different types of Lissoclinum macrocyclic peptides which are connected via two azobenzene units. The container is controllable by light: irradiation with UV light causes a switching process to the compact cis,cis-isomer, whereas by the use of visible light the stretched trans,trans-isomer is formed. By means of quantum chemical calculations and CD spectroscopy we could show that the trans→cis isomerization is spatially directed; that means that one of the two different macrocycles performs a definite clockwise rotation to the other, caused by irradiation with UV light. For the cis→trans isomerization counterclockwise rotations are found. Furthermore, quantum chemical calculations reveal that the energy of the cis,cis-isomer is only slightly higher than the energy of the cis,trans-isomer. This effect can be explained by the high dispersion energy in the compact cis,cis-isomer.