Photoisomerization Of Stilbene Research Articles

Ultrafast Raman observation of the perpendicular intermediate phantom state of stilbene photoisomerization.

Trans-cis photoisomerization is generally described by a model in which the reaction proceeds via a common intermediate having a perpendicular conformation around the rotating bond, irrespective of from which isomer the reaction starts. Nevertheless, such an intermediate has yet to be identified unambiguously, and it is often called the 'phantom' state. Here we present the structural identification of the common, perpendicular intermediate of stilbene photoisomerization using ultrafast Raman spectroscopy. Our results reveal ultrafast birth and decay of an identical, short-lived transient that exhibits a vibrational signature characteristic of the perpendicular state upon photoexcitation of the trans and cis forms. In combination with ab initio molecular dynamics simulations, it is shown that the photoexcited trans and cis forms are funnelled off to the ground state through the same, perpendicular intermediate.

Interpenetrating 3D Covalent Organic Framework for Selective Stilbene Photoisomerization and Photocyclization

The selective photoisomerization or photocyclization of stilbene to achieve value upgrade is of great significance in industry applications, yet it remains a challenge to accomplish both of them through a one-pot photocatalysis strategy under mild conditions. Here, a sevenfold interpenetrating 3D covalent organic framework (TPDT-COF) has been synthesized through covalent coupling between N,N,N,N-tetrakis(4-aminophenyl)-1,4-benzenediamine (light absorption and free radical generation) and 5,5'-(2,1,3-benzothiadiazole-4,7-diyl)bis[2-thiophenecarboxaldehyde] (catalytic center). The thus-obtained sevenfold interpenetrating structure presents a functional pore channel with a tunable photocatalytic ability and specific pore confinement effect that can be applied for selective stilbene photoisomerization and photocyclization. Noteworthily, it enables photogeneration of cis-stilbene or phenanthrene with >99% selectivity by simply changing the gas atmosphere under mild conditions (Ar, SeleCis. > 99%, SelePhen. < 1% and O2, SeleCis. < 1%, and SelePhen. > 99%). Theoretical calculations prove that different gas atmospheres possess varying influences on the energy barriers of reaction intermediates, and the pore confinement effect plays a synergistically catalytic role, thus inducing different product generation. This study might facilitate the exploration of porous crystalline materials in selective photoisomerization and photocyclization.

Twisted organic TADF triads based on a diindolocarbazole donor for efficient photoisomerization of stilbene and photo-arylation of heteroarenes

Twisted D–A TADF triads DI-PF and DI-PI based on a diindolocarbazole donor and dibenzo[a,c]phenazine (PF) and phenanthro[9,10-d]imidazole (PI) acceptors were utilized for E–Z photoisomerization of stilbene and C–H arylation of heteroarenes.

A catalyzed E/Z isomerization mechanism of stilbene using para-benzoquinone as a triplet sensitizer.

Sensitizer molecules affect not only the quantum yield but also the selectivity of photochemical reactions. For an appropriate design of sensitized photochemical processes, we need to elucidate the reaction mechanism in detail. Here we investigated the mechanism of photoisomerization of stilbene via the triplet state with a para-benzoquinone sensitizer using density functional theory. In general, the isomerization of stilbene via the triplet state exhibits (Z)-selectivity (cis-selectivity); however, the para-benzoquinone sensitizer changes it to (E)-selectivity (trans-selectivity). The calculations showed that stilbene and para-benzoquinone form stable exciplexes having a preoxetane structure. The E/Z isomerization occurred via this exciplex, in which para-benzoquinone acted as a photocatalyst rather than a sensitizer only providing excitation energy. The spin-density distribution of the exciplex differed from the isolated stilbene in the triplet state. Therefore, the stilbene moiety could take (E)-conformation in the exciplex. The intermolecular charge-transfer drove the exciplex formation. This specific reaction mechanism originated from the electron-accepting ability of para-benzoquinone in the triplet state.

Stability and Photoisomerization of Stilbenes Isolated from the Bark of Norway Spruce Roots.

Stilbenes or stilbenoids, major polyphenolic compounds of the bark of Norway spruce (Picea abies L. Karst), have potential future applications as drugs, preservatives and other functional ingredients due to their antioxidative, antibacterial and antifungal properties. Stilbenes are photosensitive and UV and fluorescent light induce trans to cis isomerisation via intramolecular cyclization. So far, the characterizations of possible new compounds derived from trans-stilbenes under UV light exposure have been mainly tentative based only on UV or MS spectra without utilizing more detailed structural spectroscopy techniques such as NMR. The objective of this work was to study the stability of biologically interesting and readily available stilbenes such as astringin and isorhapontin and their aglucones piceatannol and isorhapontigenin, which have not been studied previously. The effects of fluorescent and UV light and storage on the stability of trans stilbenes were assessed and the identification and characterisation of new compounds formed during our experiments were carried out by chromatographic (HPLC, GC) and spectroscopic techniques (UV, MS, NMR). The stilbenes undergo a trans to cis isomerisation under extended UV irradiation by intramolecular cyclisation (by the formation of a new C-C bond and the loss of two hydrogens) to phenanthrene structures. The characterised compounds are novel and not described previously.

Stiff-Stilbene Photoswitches: From Fundamental Studies to Emergent Applications.

Stiff‐stilbene, a sterically restricted fused ring analogue of stilbene, has been regularly used as a model compound in theoretical studies of stilbene photoisomerization. Lately, owing to its excellent photoswitching properties, it is increasingly being applied to reversibly control the properties and function of chemical as well as biological systems. Stiff‐stilbene photoswitches possess a number of advantageous properties including a high quantum yield for photoisomerization and a high thermal stability. Furthermore, they undergo a large geometrical change upon isomerization and their synthesis is straightforward. Herein, we provide an overview of the basic properties of stiff‐stilbene and of recent applications in supramolecular chemistry, catalysis, and biological systems.

Stiff‐Stilbene Photoswitches: From Fundamental Studies to Emergent Applications

AbstractStiff‐stilbene, a sterically restricted fused ring analogue of stilbene, has been regularly used as a model compound in theoretical studies of stilbene photoisomerization. Lately, owing to its excellent photoswitching properties, it is increasingly being applied to reversibly control the properties and function of chemical as well as biological systems. Stiff‐stilbene photoswitches possess a number of advantageous properties including a high quantum yield for photoisomerization and a high thermal stability. Furthermore, they undergo a large geometrical change upon isomerization and their synthesis is straightforward. Herein, we provide an overview of the basic properties of stiff‐stilbene and of recent applications in supramolecular chemistry, catalysis, and biological systems.

Aptamer adaptive binding assessed by stilbene photoisomerization towards regenerating aptasensors

Fluorescent aptasensors are reliant on static fluorescence intensity measurements, which suffer drawbacks such as background interference and laborious separation procedures. A unique aptasensor based on the photochrome aptamer switch assay (PHASA) has been developed that is independent of background fluorescence, requires no analyte separation, and allows rapid quantification within seconds. Malachite green aptamer (MGA) conjugated with a water-soluble stilbene on the MGA 3′ C38 terminus was chosen for building the proof-of-concept aptasensor. In the presence of malachite green and tetramethylrosamine ligands, the rate of the stilbene fluorescence decay was found to be linearly dependent on the ligand concentration. Molecular dynamic simulation suggests hydrogen bonding between stilbene sulfonates and neighboring nucleotides is the primary mechanism responsible for rate changes in stilbene photoisomerization. Analysis of the apparent fluorescence decay rate (kapp) versus analyte concentration gives a limit of detection (LOD) of 2μM for MG and 0.6μM for TMR. This aptasensor design opens up a new sensing mode, which is promising for rapid development of SELEX generated molecular recognition elements.

Phototunable Christiansen Color Filter Using Photoisomerization of Stilbene

We report a fabrication of a phototunable color filter by combining the Christiansen filter effect and photoisomerization of stilbene. It is known that stilbene isomerizes by irradiation with light, but in that case the light absorption capacity changes only in the ultraviolet region. However, the change in the refractive index due to the isomerization is reflected in the visible light region. A system in which glass beads were dispersed in a solution containing dissolved stilbene as a photochromic dye exhibited a vivid color due to the Christiansen filter effect, in spite of the lack of pigment color. Additionally, we found that the hue of the system can be changed by the isomerization of stilbene upon irradiation with ultraviolet light.

Photoinduced Bilayer-to-Nonbilayer Phase Transition of POPE by Photoisomerization of Added Stilbene Molecules.

The photocontrol of a bilayer-to-nonbilayer phase transition (the liquid-crystalline Lα phase to the inverted hexagonal HII phase) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) by the photoisomerization of incorporated stilbene molecules was examined by utilizing differential scanning calorimetry, small-angle X-ray diffraction, ultraviolet (UV)/visible absorption, and attenuated total reflectance Fourier transform infrared spectroscopies. cis-Stilbene lowered the transition temperature, Th, to a greater extent than did trans-stilbene, and the difference was at most ca. 10 °C. At temperatures higher than the Th of POPE/cis-stilbene but lower than that of POPE/trans-stilbene, the photoisomerization from the trans to the cis form of the stilbene molecules by irradiation with UV light caused a Lα-HII phase transition. The UV irradiation partially induced the HII phase at a constant temperature because of the incomplete photoisomerization of stilbene (ca. 60%). The reduction in Th by the incorporation of stilbenes was caused mainly by the reduction in the spontaneous radius of curvature of the lipid monolayer, R0. The greater bulkiness of cis-stilbene as compared to the trans form resulted in a more effective reduction in R0 and stabilization of the HII phase.

Stilbene photoisomerization driving force as revealed by the topology of the electron density and QTAIM properties

The photoisomerization of stilbene (C14H12) has become an archetype for the study of cis-trans isomerizations induced by light. Despite the many electronic structure calculations performed to gain understanding about this important process, no insight about this reaction has been obtained by means of the exploitation of topological quantum chemical methods. This contribution addresses the changes of the topology of the electron density along with those of the properties of atoms in molecules undergone throughout this photochemical transformation. By considering the phenyl rings and the CHCH bridge of stilbene separately, we found that both groups in the ground state are destabilized when the system evolves from either the cis or trans isomer towards the conical intersection connecting the S0 and S1 states. Nonetheless, the energy of the C6H5 moieties across the excited state potential energy curve is reduced along the same change in configuration of C14H12, thereby providing the driving force for the reaction to occur. The analysis of the atomic charges reveals that the carbon atoms of the CHCH bridge withdraw electron density from their interatomic region between them and the phenyl groups. This flow of charge density might be related with the occupation of the CHCH π★ orbital which allows the reaction to take place. Finally, an examination of the electronegativity of the groups CHCH and C6H5 indicates that the phenyl rings drastically change their electronegative nature upon photoexcitation, enabling the system to undergo the photoisomerization. Overall, it is shown how the topological analysis of the electron density can provide important insights about chemical reactions carried out in excited states.

Landscapes of four-enantiomer conical intersections for photoisomerization of stilbene: CASSCF calculation.

The photoisomerization of cis- and trans-stilbene through conical intersections (CI) is mainly governed by four dihedral angles around central C═C double bonds. The two of them are C-C═C-C and H-C═C-H dihedral angles that are found to form a mirror rotation coordinate, and the mirror plane appears at the two dihedral angles equal to zeros with which the middle state is defined through partial optimization. There exist the first-type of hula-twist-CI enantiomers, the second-type of hula-twist-CI enantiomers, the first-type of one-bond-flip-CI enantiomers, and the second type of one-bond-flip-CI enantiomers as well as cis-enantiomers and trans-enantiomers with respect to this mirror plane. The complete active space self-consistent field method is employed to calculate minimum potential energy profile along the mirror rotation coordinate for each enantiomers, and it is found that the left-hand manifold and the right-hand manifold of potential energy surfaces can be energetically transferred via photoisomerization. Furthermore, two-dimensional potential energy surfaces in terms of the branching plane g-h coordinates are constructed at vicinity of each conical intersection, and the landscapes of conical intersections show distinct feature, and in excited-state four potential wells separated in different section of g-h plane related to different conical intersections which indicate different photoisomerization pathways.

Specific features of photoprocesses in molecules with a styryl group

Rate constants of photophysical processes are calculated for molecules with a styryl group (stilbene (styrylbenzene), 4-trans-styrylbiphenyl, 4-trans-styrylterphenyl, and 1,4-distyrylbenzene) using an original method based on the theory of nonradiative transitions. The values for calculations are obtained using a software package based on the method of intermediate neglect of differential overlap with spectroscopic parametrization. The results make it possible to numerically estimate the molecular parameters and effect of substituents. Torsional and twist rotations are simulated in the fluorescence structure of trans-stilbene, and the effect of these rotations on the rates of photoprocesses is analyzed. The results additionally contribute to the interpretation of excitation-energy relaxation and photoisomerization of stilbene.

Photochemistry of supramolecular complex formed by trans-stilbene and the metal–organic coordination polymer

Supramolecular adduct consisting from the metal–organic framework (MOF) [Zn4(dmf)(ur)2(ndc)4] (ndc2− is 2,6-naphtalenedicarboxylate, ur is urotropin, and dmf is N,N′-dimethylformamide) and trans-stilbene was synthesized and its photochemistry was studied. The quantum yield of trans–cis photoisomerization of stilbene in adduct (0.2) was found to be an order of magnitude higher than for crystalline trans-stilbene and comparable with that in organic solvents. The results demonstrate that the creation of MOFs adducts with organic photochroms is a prospective approach for the creation of new hybrid photochromic materials.

Computational studies of the x-ray scattering properties of laser aligned stilbene

The enhancement of the x-ray scattering signal from partially aligned molecular samples is investigated. The alignment properties of the studied molecular system are modeled based on the method of laser alignment. With the advances in the area of laser alignment of molecules, the application of this sample manipulation technique promises a great potential for x-ray scattering measurements. Preferential alignment of molecules in an otherwise amorphous sample leads to constructive interference and thus increases the scattering intensity. This enhances the structural information encoded in the scattering images and enables improved resolution in studies of reaction dynamics, as in this work is shown for the example of the photo-isomerization of stilbene. We demonstrate that the scattering signal is strongly influenced by the alignment axis. Even the most basic one-dimensional alignment offers significant improvement compared to the structural information provided by a randomly oriented sample. Although the signal is sensitive to the uncertainty in the alignment angle, it offers encouraging results even at realistic alignment uncertainties.

The Catalytic Z to E Isomerization of Stilbenes in a Photosensitizing Porous Coordination Network

One way only: The Z→E photoisomerization of stilbene under visible light occurs within a porous coordination network (see picture). The reaction proceeds through the photoexcitation of a charge-transfer complex between the highly electron-deficient ligand and the stilbene in the pore. The in situ formed E isomer rapidly exchanges with unreacted Z isomer in solution, hence a catalytic amount of the network is sufficient to promote the reaction.

Trans-to- cis isomerization of stilbene following an ultrafast laser pulse

Dynamical simulations are reported for trans-to- cis photoisomerization of stilbene induced by a femtosecond-scale laser pulse. The results imply that the basic mechanism is the simplest imaginable: Electronic excitation by the laser pulse weakens the central C–C bond, and also excites vibrations of this bond. Vibrational energy redistribution then leads to rotation about the bond, resulting in isomerization. Finally, electronic de-excitation near a conical intersection restores the molecule to the electronic ground state. On the other hand, these dynamical simulations demonstrate complexity in the details and reveal supporting roles for other degrees of freedom, such as torsional motion about the vinyl-phenyl side bonds.

The Role of Organic Glasses in cis/trans Photoisomerization at Low Temperatures

Low temperature photoisomerization of stilbene and 1,4-diphenyl-1,3-butadiene derivatives was found to vary depending on the organic glass employed in such studies. Examination of the combined results showed that the variation was more likely to arise from the rigidity of the organic glass at the temperature of irradiation rather than the composition of the organic glass; that is, the observed results are consistent with the possible softening of the glass that surrounds the excited substrate in the same manner as detected in the photolysis of ethyl iodide reported by Porter and co-workers. These observations successfully account for the apparent "disagreement" of reports from the Hawaii and the Florida State groups on the mechanism of photoisomerization in low temperature glasses.

Ab initio treatment of time-resolved x-ray scattering: Application to the photoisomerization of stilbene

In this work we present a general theoretical outline for calculating time-dependent x-ray scattering signal changes from first principles. We derive a formalism for the description of atom-atom correlation functions as Fourier transforms of quantum-chemically calculated electron densities and show their proportionality to the molecular form factor. The formalism derived in this work is applied to the photoisomerization of stilbene. We can demonstrate that wide-angle x-ray scattering offers a possibility to study the changes in electron densities in nonperiodic complex systems, which renders it a suitable technique for the investigation of (bio)organic systems.

Detailed dynamics of a complex photochemical reaction: Cis–trans photoisomerization of stilbene

Detailed simulations are reported for the dynamics of electrons and nuclei during the cis to trans photoisomerization of stilbene. Our method, which employs a semiclassical description of both the nuclear motion and the radiation field, is described in the text. After excitation of electrons from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) by a femtosecond-scale laser pulse, two principal avoided crossings are observed between the HOMO and LUMO levels, each of which leads to substantial depopulation of the LUMO. Based on our results and those of other groups, we propose that the first such HOMO–LUMO coupling can lead to the formation of 4a,4b-dihydrophenanthrene (DHP). The second coupling, on the other hand, leads to the formation of trans-stilbene. It is found that pyramidalization of the two carbon atoms of the vinyl group is involved significantly in both couplings, and that rotation of the two phenyl rings, together with their interaction, plays an important role in the first coupling. The occurrence along the same trajectory of two couplings, one leading to DHP and the other leading to isomerization, is a significant observation, and one which indicates that further theoretical and experimental investigations would be of considerable interest.