Trans-cis Photoisomerization Research Articles

Modelling ultrafast dynamics at a conical intersection with regularized diabatic states: An approach based on multiplicative neural networks

• Neural network (NN) potentials for quantum dynamics of cis–trans photoisomerization. • Multiplicative NNs adapted to regularized diabatic states at a conical intersection. • NN potentials match a sum-of-products form required by MCTDH wavefunction propagation. • Good agreement found for highly correlated dynamics with up to 13 degrees of freedom. Neural-network (NN) potentials are employed in conjunction with the Multiconfiguration Time-Dependent Hartree (MCTDH) method in order to simulate an ultrafast photoinduced cis–trans type isomerization process induced by a conical intersection. To this end, NN potentials are fitted to a diabatic potential of regularized diabatic states type [Köppel et al., J. Chem. Phys. 115, 2377 (2001)], which entirely relies on adiabatic potential information. Multiplicative NNs are employed which match the sum-of-products form of the multiconfigurational MCTDH wavefunction. Good agreement with the reference dynamics is obtained for simulations of the highly correlated dynamics with up to 13 degrees of freedom. This study contributes to developing NN methodologies suitable for photochemical dynamics at complex excited-state topologies.

Cytotoxicity and Genotoxicity of Azobenzene-Based Polymeric Nanocarriers for Phototriggered Drug Release and Biomedical Applications.

Drug nanoencapsulation increases the availability, pharmacokinetics, and concentration efficiency for therapeutic regimes. Azobenzene light-responsive molecules experience a hydrophobicity change from a polar to an apolar tendency by trans–cis photoisomerization upon UV irradiation. Polymeric photoresponse nanoparticles (PPNPs) based on azobenzene compounds and biopolymers such as chitosan derivatives show prospects of photodelivering drugs into cells with accelerated kinetics, enhancing their therapeutic effect. PPNP biocompatibility studies detect the safe concentrations for their administration and reduce the chance of side effects, improving the effectiveness of a potential treatment. Here, we report on a PPNP biocompatibility evaluation of viability and the first genotoxicity study of azobenzene-based PPNPs. Cell line models from human ventricular cardiomyocytes (RL14), as well as mouse fibroblasts (NIH3T3) as proof of concept, were exposed to different concentrations of azobenzene-based PPNPs and their precursors to evaluate the consequences on mitochondrial metabolism (MTT assay), the number of viable cells (trypan blue exclusion test), and deoxyribonucleic acid (DNA) damage (comet assay). Lethal concentrations of 50 (LC50) of the PPNPs and their precursors were higher than the required drug release and synthesis concentrations. The PPNPs affected the cell membrane at concentrations higher than 2 mg/mL, and lower concentrations exhibited lesser damage to cellular genetic material. An azobenzene derivative functionalized with a biopolymer to assemble PPNPs demonstrated biocompatibility with the evaluated cell lines. The PPNPs encapsulated Nile red and dofetilide separately as model and antiarrhythmic drugs, respectively, and delivered upon UV irradiation, proving the phototriggered drug release concept. Biocompatible PPNPs are a promising technology for fast drug release with high cell interaction opening new opportunities for azobenzene biomedical applications.

Electrical transport and NDR property on the cis–trans photo-isomerization of (1R,3S)-2,2-dimethyl-3-(2-methylprop-1-en-1-yl)cyclopropanecarboxylate as an optical molecular switch; A DFT-NEGF study

A first-principles method joined to non-equilibrium Green’s function (NEGF) is used to study the transport of (1R,3S)-2,2-dimethyl-3-(2-methylprop-1-en-1-yl)cyclopropanecarboxylate (Allethrin) as an optical molecular switch. The voltage-current curves were indicated that the current of cis isomer dramatically more than the trans isomer. Some parameters, such as electrode type’s (Au, Pt, and Ag) and connection sites (top, bridge, and hollow), I–V curves, on/off ratios, transmittance spectra, and projected density of states (PDOS) have been studied. The outcomes for cis isomer of Allethrin molecular junction demonstrate that negative differential resistance (NDR) behavior is detected in all electrodes and adsorption sites at high voltages.

Steady State Photoisomerization Quantum Yield of Model Rhodopsin: Insights from Wavepacket Dynamics?

We simulate the nonequilibrium steady state cis-trans photoisomerization of retinal chromophore in rhodopsin on the basis of a two-state, two-mode model coupled to a thermal environment. By analyzing the systematic trends within an inhomogeneously broadened ensemble of systems, we find that the steady state reaction quantum yield (QY) correlates strongly with the excess energy above the crossing point of the system, in agreement with the prediction of the short-time dynamical wavepacket picture. However, the nontrivial dependence of the QY on the system-environment interaction indicates that a pure dynamical picture is insufficient and that environment-induced partial internal energy redistribution takes place before the reaction concludes. These results imply that a proper treatment of the photoisomerization reaction, particularly its high QY, must account for the redistribution and dissipation of energy beyond the dynamical wavepacket motion that is typically employed in the literature and that is appropriate only in the transient regime.

The Photocycle of Bacteriophytochrome Is Initiated by Counterclockwise Chromophore Isomerization.

Photoactivation of bacteriophytochrome involves a cis–trans photoisomerization of a biliverdin chromophore, but neither the precise sequence of events nor the direction of the isomerization is known. Here, we used nonadiabatic molecular dynamics simulations on the photosensory protein dimer to resolve the isomerization mechanism in atomic detail. In our simulations the photoisomerization of the D ring occurs in the counterclockwise direction. On a subpicosecond time scale, the photoexcited chromophore adopts a short-lived intermediate with a highly twisted configuration stabilized by an extended hydrogen-bonding network. Within tens of picoseconds, these hydrogen bonds break, allowing the chromophore to adopt a more planar configuration, which we assign to the early Lumi-R state. The isomerization process is completed via helix inversion of the biliverdin chromophore to form the late Lumi-R state. The mechanistic insights into the photoisomerization process are essential to understand how bacteriophytochrome has evolved to mediate photoactivation and to engineer this protein for new applications.

Generation of sub-micrometer surface relief gratings in an azobenzene-containing material using a 355 nm laser

Controlled effective fabrication of surface relief gratings (SRG) of different periods and dimensionality in an azobenzene-containing polyelectrolyte material using an UV-laser operating at 355 nm was demonstrated for the first time. The application of an UV-laser in combination with Lloyd's interferometer allows the accurate control of grating period and the generation of gratings with small period down to 180 nm. The SRG formation is related to the kinetics of the steady state of the trans-cis photoisomerization of a PAZO film at UV exposure. The replication of the manufactured gratings using soft lithography is demonstrated as well.

Photopharmacological Tools for Mitotic Cell Division

Genetic information is replicated and transmitted from a parent cell to two identical daughter cells through mitotic cell division. To accomplish this dynamic process with high accuracy and precision, various motor proteins work in a concerted manner. Especially in the metaphase, mitotic chromosomes are delivered by the motor protein of centromere-associated protein E (CENP-E) to the cell equatorial plane (metaphase plate) along mitotic spindles. However, the critical functional failure of CENP-E can activate the spindle assembly checkpoint through the misalignment of chromosomes at the metaphase plate. In this symposium review, the reversibly photoswitchable CENP-E inhibitor PCEI-HU (5) is reported. Compound 5 exhibited almost quantitative trans-cis photoisomerization of the arylazopyrazole photoswitch by illuminating light at 365 nm and 510 nm. Depending on the photoisomerization, CENP-E activity was regulated not only in vitro but also in cells. We successfully established a novel technique using 5 to dynamically photocontrol the CENP-E-dependent chromosome movement and mitotic progression in a living cell.

DNA/Protein binding and anticancer activity of Zn(II) complexes based on azo-Schiff base ligands

Synthesis of the azo–Schiff base ligands 2-((E)-((4-(diethylamino)phenyl)imino)methyl)-4-((E)-(2-(phenylthio)phenyl)diazenyl)phenol (L1) and-((E)-((4-(diethylamino)phenyl)-imino)methyl)-4-((E)-(2-phenoxyphenyl)diazenyl)phenol (L2) and Zn(II) complexes (C1-C2) containing these ligands have been described. Characterization of the ligands and complexes has been achieved by spectral studies (IR, 1H, 13C, ESI–MS, UV/vis., emission) and structures of C1 and C2 verified by X-ray single crystal analyses. Absorption titration studies on the complexes revealed that these strongly interact with calf thymus DNA (CT-DNA). Calculated equilibrium binding constants (Kb) for C1 and C2 converged to 4.51 × 104 and 3.74 × 104. Protein binding studies of the complexes with BSA have been performed by UV/vis, fluorescence, synchronous and 3D fluorescence spectroscopy. MTT assay toward Hut-78 cell line suggested high cytotoxicity for C1 (IC50: 70 μM) relative to C2 (IC50: 110 µM). Upon irradiation (UV light; λ, 365 nm) the complexes C1 and C2 exhibited cis–trans photo isomerization and after withdrawal of the light these settled back to more stable trans form. Rate constant (k) for photo isomerization of C1 and C2 has been worked out using electronic absorption data (2.29 × 10−2,C1; 2.12 × 10−2 s−1, C2) and supported by theoretical studies (DFT).

Quantum dynamics with curvilinear coordinates: models and kinetic energy operator.

In order to simplify the numerical solution of the time-dependent or time-independent Schrödinger equations associated with atomic and molecular motions, the use of well-adapted coordinates is essential. Usually, this set of curvilinear coordinates leads to a Hamiltonian operator that is as separable as possible. Although their corresponding kinetic energy operator (KEO) expressions can be derived analytically for small systems or special kinds of coordinates, a numerical and exact approach allows one to compute them in terms of sophisticated curvilinear coordinates. Furthermore, the numerical approach enables one to easily define reduced-dimensionality or constrained models. We present here a recent implementation of this numerical approach that allows nested coordinate transformations, therefore leading to great flexibility in the definition of the curvilinear coordinates. Furthermore, this implementation has no limitations in terms of numbers of atoms or coordinate transformations. The quantum dynamics of the cis-trans photoisomerization of part of the retinal chromophore illustrates the construction of the coordinates and KEO part of a three-dimensional model. This article is part of the theme issue 'Chemistry without the Born-Oppenheimer approximation'.

Photoinduced phase transition of N-benzylideneaniline liquid crystalline polymer and applications of photodismantlable adhesives

The liquid crystalline N-benzylideneaniline (NBA) polymer acts as an adhesive, and its bonded pieces detach upon exposure to UV light due to the trans-cis photoisomerization of the NBA moieties and subsequent phase transition of NBA from a liquid crystal polymer to an isotropic polymer. We improved the photoresponsive durability of the polymer and explored the effect of light irradiation on its thermal properties and adhesion stress. We observed that the transition points of the polymer's thermophysical properties (glass transition, liquid crystal-isotropic transition, G" slope, tan δ) shifted to lower temperatures under light irradiation.

A Mononuclear Iron(II) Spin-Crossover Molecule Decorated by Photochromic Azobenzene Group.

Aiming at constructing photoresponsive spin crossover (SCO) behavior, herein we designed a new ligand Abtz (Abtz = (E)-N-(4-((E)-phenyldiazenyl)phenyl)-1-(thiazol-4-yl)methanimine) which was decorated by a photochromic azobenzene group. Based on this photochromic ligand, a mononuclear Fe(II) SCO molecule [Fe(Abtz)3](BF4)2·(EAC)2 (1, EAC = ethyl acetate) was successfully synthesized and showed a complete one-step SCO behavior. Under continuous UV light and blue-light exposure, the cis–trans photoisomerization of both ligand Abtz and compound 1 in the liquid phase was confirmed through UV–Vis spectra. Moreover, the 1H-NMR spectra of Abtz reveal a trans–cis conversion ratio of 37%. Although the UV–Vis spectra reveal the photochromic behavior for 1 in the solution phase, the SCO behavior in the liquid state is absent according to the variable-temperature Evans method, suggesting the possible decomposition. Moreover, in the solid state, the cis–trans photoisomerization of both Abtz and 1 was not observed, due to the steric hindrance.

Substituent and Solvent Effects on the Photoisomerization of Cinnamate Derivatives: An XMS-CASPT2 Study.

Cinnamate derivatives show a variety of photo-induced reactions. Among them is trans-cis photoisomerization, which may involve the nonradiative decay (NRD) process. The extended multistate complete active space second-order perturbation (XMS-CASPT2) method was used in this study as a suitable theory for treating multireference electronic nature, which was frequently manifested in the photoisomerization process. The minimum energy paths of the trans-cis photoisomerization process of cinnamate derivatives were determined, and the activation energies were estimated using the resulting intrinsic reaction coordinate (IRC) paths. Natural orbital analysis revealed that the transition state's (TS) electronic structure is zwitterionic-like, elucidating the solvent and substituent effect on the energy barrier of photoisomerization paths. Furthermore, it was found that the charge on the pyramidalized carbon atom at the TS structure was strongly correlated with the activation energy barrier for the cinnamate derivatives. Thus, it seemingly provided a physical picture of the photoisomerization of cinnamates and was a good descriptor potentially applicable to molecular design for controlling the rate constant of the photoisomerization reaction.

Photoswitching of 5-phenylazopyrimidines in crystalline powders and thin films

Solid-state photoswitching enables the development of smart materials. However, the close packing of molecules and the lack of free volume in this state prevent sterically demanding structural changes induced by irradiation, thereby precluding the use of azobenzene photoswitches. Nevertheless, we report here the solid-state photoswitching of their derivatives, 5-phenylazopyrimidines, in crystalline powders and in amorphous thin layers. After identifying trans-cis photoisomerization by NMR spectroscopy, we demonstrated the applicability of 5-phenylazopyrimidines for future all-optical switching applications. For this purpose, we prepared thin films by spin-coating and confirmed their solid-state optical switching by optical transmission spectroscopy and their favorable surface topography by atomic force microscopy. Therefore, thin films of 5-phenylazopyrimidines are suitable for on-chip integration for emerging all-optical technologies.

Visible light, temperature, and electric field-driven rotation of diffraction gratings enabled by an axially chiral molecular switch

A visible light-driven chiral molecular switch shows reversibletrans–cisphotoisomerization, good compatibility, and high helical twisting power in achiral liquid crystals. Multi-stimuli responsive rotatable in-plane beam steering and chromatic dispersion are accomplished.

Multi-objective optimization for retinal photoisomerization models with respect to experimental observables

The fitting of physical models is often done only using a single target observable. However, when multiple targets are considered, the fitting procedure becomes cumbersome, there being no easy way to quantify the robustness of the model for all different observables. Here, we illustrate that one can jointly search for the best model for each desired observable through multi-objective optimization. To do so, we construct the Pareto front to study if there exists a set of parameters of the model that can jointly describe multiple, or all, observables. To alleviate the computational cost, the predicted error for each targeted objective is approximated with a Gaussian process model as it is commonly done in the Bayesian optimization framework. We applied this methodology to improve three different models used in the simulation of stationary state cis-trans photoisomerization of retinal in rhodopsin, a significant biophysical process. Optimization was done with respect to different experimental measurements, including emission spectra, peak absorption frequencies for the cis and trans conformers, and energy storage. Advantages and disadvantages of previously proposed models are exposed.

Guest‐Driven Light‐Induced Spin Change in an Azobenzene Loaded Metal–Organic Framework

AbstractStimuli‐responsive materials that can be reversibly switched by light are of immense interest. Among them, photo‐responsive spin crossover (SCO) complexes have great promises to combine the photoactive inputs with multifaceted outputs into switchable materials and devices. However, the reversible control the spin‐state change by photochromic guests is still challenging. Herein, we report an unprecedented guest‐driven light‐induced spin change (GD‐LISC) in a Hofmann‐type metal–organic framework (MOF), [Fe(bpn){Ag(CN)2}2]⋅azobenzene. (1, bpn=1,4‐bis(4‐pyridyl)naphthalene). The reversible trans–cis photoisomerization of azobenzene guest upon UV/Vis irradiation in the solid‐state results in the remarkable magnetic changes in a wide temperature range of 10–180 K. This finding not only establishes a new switching mechanism for SCO complexes, but also paves the way toward the development of new generation of photo‐responsive magnetic materials.

Guest-Driven Light-Induced Spin Change in an Azobenzene Loaded Metal-Organic Framework.

Stimuli-responsive materials that can be reversibly switched by light are of immense interest. Among them, photo-responsive spin crossover (SCO) complexes have great promises to combine the photoactive inputs with multifaceted outputs into switchable materials and devices. However, the reversible control the spin-state change by photochromic guests is still challenging. Herein, we report an unprecedented guest-driven light-induced spin change (GD-LISC) in a Hofmann-type metal-organic framework (MOF), [Fe(bpn){Ag(CN)2 }2 ]⋅azobenzene. (1, bpn=1,4-bis(4-pyridyl)naphthalene). The reversible trans-cis photoisomerization of azobenzene guest upon UV/Vis irradiation in the solid-state results in the remarkable magnetic changes in a wide temperature range of 10-180 K. This finding not only establishes a new switching mechanism for SCO complexes, but also paves the way toward the development of new generation of photo-responsive magnetic materials.

Combined electric and photocontrol of selective light reflection at an oblique helicoidal cholesteric liquid crystal doped with azoxybenzene derivative.

An oblique helicoidal cholesteric liquid crystal Ch_{OH} represents a unique optical material with a single-harmonic periodic modulation of the refractive index and a pitch that can be tuned by an electric or magnetic field in a broad range from submicrometers to micrometers. In this work, we demonstrate that the oblique helicoidal cholesteric doped with azoxybenzene molecules can be tuned by both the electric field and light irradiation. The tuning mechanism is explained by the kinetics of trans-cis photoisomerization of the azoxybenzene molecules. At a fixed voltage, UV irradiation causes a redshift of the reflection peak by more than 200 nm. The effect is caused by an increase of the bend elastic constant of Ch_{OH} under irradiation. The demonstrated principle has the potential for applications such as smart windows, sensors, tunable lasers, and filters.

Microbial Rhodopsins as Multi-functional Photoreactive Membrane Proteins for Optogenetics.

In life science research, methods to control biological activities with stimuli such as light, heat, pressure and chemicals have been widely utilized to understand their molecular mechanisms. The knowledge obtained by those methods has built a basis for the development of medicinal products. Among those various stimuli, light has the advantage of a high spatiotemporal resolution that allows for the precise control of biological activities. Photoactive membrane protein rhodopsins from microorganisms (called microbial rhodopsins) absorb visible light and that light absorption triggers the trans-cis photoisomerization of the chromophore retinal, leading to various functions such as ion pumps, ion channels, transcriptional regulators and enzymes. In addition to their biological significance, microbial rhodopsins are widely utilized as fundamental molecular tools for optogenetics, a method to control biological activities by light. In this review, we briefly introduce the molecular basis of representative rhodopsin molecules and their applications for optogenetics. Based on those examples, we discuss the high potential of rhodopsin-based optogenetics tools for basic and clinical research in pharmaceutical sciences.

Nonadiabatic Dynamics Mechanism of Chalcone Analogue Sunscreen FPPO-HBr: Excited State Intramolecular Proton Transfer Followed by Conformation Twisting.

Nowadays, traditional sunscreen molecules face many adverse problems: single energy relaxation pathway, lack of adequate UVA light protection, and therefore no longer meeting the growing demand for UVA protection. In this work, we reported a novel sunscreen molecule (E)-3-(5-bromofuran-2-yl)-1-(2-hydroxyphenyl)prop-2-en-1-one (hereinafter referred to as FPPO-HBr) which tackled adverse problems of traditional sunscreen molecules as single energy relaxation pathway, lacking effective UVA light protection. Various nonradiative pathways were proposed and verified by combining the steady-state and femtosecond transient absorption (FTA) spectroscopy and theoretical calculation. Upon UV excitation, the FPPO-HBr mainly decays via excited-state intramolecular proton transfer (ESIPT) followed by conformation twist in ultrafast manner. Importantly, 1H NMR spectra proved that the FPPO-HBr could not undergo trans-cis photoisomerization. Additionally, excellent photostability was also observed for newly synthesized FPPO-HBr. The current work could provide new perspectives for sunscreen molecules synthesis and mechanism.