Photoisomerization of diarylethylenes

Conclusions The absolute quantum yields of fluorescence and cis trans photoisomerization for naphthylethylenes in liquid and solid solutions at room temperature were measured by the methods of fluorescence and spectrophotometry.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 298–306, February, 1975.     

Photoisomerization of Phenylazoalkenes

(E)-Phenylazocyclohexene ( 1 ) undergoes photoisomerization to s-cis-(Z)-phenylazocyclohexene ( 2 ). Compound 2 reisomerizes to 1 at room temperature.     

Photoisomerization kinetics of trifloxystrobin

The photoisomerization kinetics of trifloxystrobin (TFS) in acetone under artificial sunlight is reported. HPLC analysis showed the TFS, a strobilurine fungicide of EE conformation, was converted into an equilibrium mixture of four isomers after illumination for 7 h. The isomers were identified as EZ, EE, ZZ, and ZE and were separated in the crystalline form by preparative HPLC and characterized by use of a variety of spectroscopic techniques. The quantum yield and reaction constants for the isomerization reactions were determined. The detailed spectral features of the individual isomers measured by UV, IR, Raman, NMR and mass spectroscopy are presented and compared. The spectra of the isomers were found to be very characteristic, with good analytical significance.     

Photoisomerization of octyl methoxycinnamate

The octyl-p-methoxy-trans-cinnamate (E-OMC) was exposed to sunlight to induce the E to Z transformation. Octyl-p-methoxy-cis-cinnamate (Z-OMC) was then purified from the mixture of the E- and the Z-OMC using C-18-semi-preparative HPLC. The UV absorption of the Z configuration at various concentrations in various solvents was measured. Molar absorption coefficient of the compound was then calculated. By using the obtained molar absorption coefficient of Z-OMC and of E-OMC, E to Z photoisomerization of octyl methoxycinnamate (OMC) in various solvents at various concentrations could be monitored by C-18 HPLC using UV detector. The result indicates that equilibrium of photoisomerization depends upon concentration and polarity of the solvent used.     

Moving Polymers via Photoisomerization

Photoresponsive materials, which can adapt their states and shapes upon light irradiation, have attracted worldwide attention in the past decades. The development of azobenzene‐containing polymers (azopolymers) opens up an avenue for controlling their properties and functions with light. These polymers show shape changes and mechanical responses under the stimulation of light via photoisomerization of azobenzene groups. Herein, this report focuses on the growing research on moving polymers via photoisomerization, including their moving mechanisms and various applications.     

Theoretical Study on Photoisomerization of 2-Methylfuran to 3-Methylfuran

1 INTRODUCTION 2-Methylfuran belongs to the basic heteroaromatic compounds relevant to many fields of modern che- mistry, ranging from the study of natural products and biologically active substances to the develop- ment of building blocks for organic synthesis and conducting polymers[1]. Since the photochemistry ofR-furan was gradually recognized in 1960s[2～7], lots of interest has been aroused. Herein we only study one branch of photoche- mistry of R-furan: the isomerization of 2-methy…     

Photoisomerization in different classes of azobenzene

Azobenzene undergoes trans→cis isomerization when irradiated with light tuned to an appropriate wavelength. The reverse cis→trans isomerization can be driven by light or occurs thermally in the dark. Azobenzene's photochromatic properties make it an ideal component of numerous molecular devices and functional materials. Despite the abundance of application-driven research, azobenzene photochemistry and the isomerization mechanism remain topics of investigation. Additional substituents on the azobenzene ring system change the spectroscopic properties and isomerization mechanism. This critical review details the studies completed to date on the 3 main classes of azobenzene derivatives. Understanding the differences in photochemistry, which originate from substitution, is imperative in exploiting azobenzene in the desired applications.     

2-甲基噻吩光异构化成3-甲基噻吩的理论研究

用CASSCF方法以6-31G基组研究了2-甲基噻吩光异构化为3-甲基噻吩的光化学反应和基态(S₀)及三重激发态(T₁)的相关势能面.反应主要发生在三重态(T₁)上,其间经历了两个双自由基,1个三元环中间体及4个过渡态.沿着反应路径找到了2个T₁/S₀势能面交叉点,其结构都类似于双自由基.在第二个T₁/S₀势能面交叉点附近由T₁向S₀的系间窜越(ISC)最为有利.     

Photoisomerization of sterically hindered polymethine dyes

Conclusions In sterically hindered polymethine dyes the photoisomerization process, with the formation of sterically hindered trans and di-cis forms, successfully competes with the nonradiative degradation of the energy on the higher vibrational sublevels of the ground state.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1926–1930, August, 1977.     

Photoisomerization and thermal isomerization of arylazoimidazoles

Photoisomerization and thermal isomerization behaviors of an extensive series of arylazoimidazoles are investigated. Absorption spectra are characterized by a structured pipi* absorption band around 330-400 nm with a tail on the lower energy side extending to 500 nm corresponding to an npi* transition. The trans-to-cis photoisomerization occurs on excitation into these absorption bands. The quantum yields are dependent on the excitation wavelength, as observed for azobenzene derivatives, but are generally larger than those of azobenzene. The thermal cis-to-trans isomerization rates are also generally larger than that of azobenzene and are comparable to those of 4-N,N-dimethylaminoazobenzene and 4-nitroazobenzene. Arylazoimidazoles with no substituent on the imidazole nitrogen are unique in that the quantum yield for the trans-to-cis photoisomerization and the rate of thermal cis-to-trans isomerization are particularly large. It is proposed that the fast thermal isomerization is due to an involvement of self-catalyzed and protic molecule-assisted tautomerization to a hydrazone form.     

Photoisomerization of chalcone: wavelength dependence

The quantum yield for the cis—trans photoisomerization of chalcone (1,3-diphenylpropen-3-one) is wavelength dependent. At 313 nm the trans-to-cis quantum yield is 0.36 and the cis-to-trans quantum yield is 0.135. At 366 nm the trans-to-cis quantum yield is 0.48 and the cis-to-trans quantum yield is 0.23. These values were not affected by changes in the concentration of chalcone or by the presence of oxygen. A comparison with the literature data is made and reasons for the quantum inefficiency and the wavelength dependence are discussed.     

Photoisomerization of dichlorocarbene adducts of 2,4-cyclohexadienones

Irradiation of the nπ* band of the dichlorocyclopropyl enones $\text{1}$ and $\text{7}$ resulted in ring expansion and 1,2-chlorine migration to give $\text{2}$ and $\text{8}$ respectively, whereas the dihydrogen analog $\text{11}$ gave the vinylcyclopropane-cyclopentene rearrangement product $\text{12}$.     

Photoisomerization of Styryl Derivatives of Pyridine N-Oxide

Russian Journal of Physical Chemistry A - The trans–cis- and cis–trans-isomerization of styryl derivatives of heterocyclic N-oxides in acetonitrile and ethanol is studied. The...     

Photoisomerization and photochemistry of matrix-isolated 3-furaldehyde

3-Furaldehyde (3FA) was isolated in an argon matrix at 12 K and studied using FTIR spectroscopy and quantum chemistry. The molecule has two conformers, with trans and cis orientation of the O=C-C=C dihedral angle. At the B3LYP/6-311++G(d,p) level of theory, the trans form was computed to be ca. 4 kJ mol(-1) more stable than the cis form. The relative stability of the two conformers was explained using the natural bond orbital (NBO) method. In fair agreement with their calculated relative energies and the high barrier of rotamerization (ca. 34 kJ mol(-1) from trans to cis), the trans and cis conformers were trapped in an argon matrix from the compound room temperature gas phase in proportion ~7:1. The experimentally observed vibrational signatures of the two forms are in a good agreement with the theoretically calculated spectra. Broad-band UV-irradiation (λ > 234 nm) of the matrix-isolated compound resulted in partial trans → cis isomerization, which ended at a photostationary state with the trans/cis ratio being ca. 1.85:1. This result was interpreted based on results of time-dependent DFT calculations. Irradiation at higher energies (λ > 200 nm) led to decarbonylation of the compound, yielding furan, cyclopropene-3-carbaldehyde, and two C(3)H(4) isomers: cyclopropene and propadiene.     

Photoisomerization of azobenzene derivatives in nanostructured silica

A series of derivatized azobenzene molecules are synthesized such that one of the phenyl groups can be chemically bonded to mesostructured silica and the other, derivatized with dendrons, is free to undergo large-amplitude light-driven motion. The silica frameworks on which the motion takes place are either 150 nm thick films containing ordered hexagonal arrays of tubes (inner diameter about 2 nm) containing the bonded azobenzenes, or particles (about 500 nm in diameter) containing the same ordered arrays of functionalized tubes. The photoisomerization yields and the rate constants for the thermal cis to trans back-reaction of the azobenzenes in the tubes are measured and compared to those of the molecules in solution. The rate constants decrease with increasing size of the dendrons. Fluorescence spectra of the cis and trans isomers in the pores show that the photoisomerization in the nanostructured materials is selectively driven by specific wavelengths of light and is reversible.     

Photoisomerization of linear merocyanines in salt solutions

The trans-cis isomerization in the excited state of linear merocyanine L-Mero4 and phenyl substituted linear merocyanine P-L-Mero4 in salt solution and in ionic liquid was investigated using frequency upconversion measurements. Strontium chloride and cesium iodide were added to solvent dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) to vary the ionic strength. The time-resolved fluorescence curves of merocyanines displayed multiple exponential decay behavior. The second temporal component with time constant τ₂ ≈ 2.8 (11) ps of L-Mero4 (P-L-Mero4) in DMSO was assigned to the duration to reach the isomerization equilibrium between the trans and the twisted conformers. The τ₂ increased at higher salt concentrations and was explained by the attachment of salt ions on the polar excited merocyanines decelerating the isomerization rate. The rotational correlation time constants obtained from the anisotropy decay of fluorescence were 360 and 240 ps in neat DMSO for L-Mero4 and P-L-Mero4, respectively, and they increased to 790 and 450 ps in the most concentrated SrCl₂. Using Perrin relation, we estimated the increase in the rotating volume at [SrCl₂] = 536 mM, revealing ≈15 SrCl₂ molecules surrounding L-Mero4 and 7 SrCl₂ on P-L-Mero4. The experimental data indicated that the ion–molecule interaction was stronger with SrCl₂ and on L-Mero4 than on P-L-Mero4.