Search results for "Photoisomerization"
showing 10 items of 73 documents
Anharmonic Vibrational Spectrum and Experimental Matrix Isolation Study of Thioformic Acid Conformers -- Potential Candidates for Molecular Cloud and…
2021
Thioformic acid (TFA) is the sulfur analog of formic acid, the simplest organic acid. It has three analogues HCOSH, HCSOH, and HCSSH, each of them having two rotational isomeric (rotameric) forms: trans and cis where the trans form is energetically more stable. In this article, we study computational energetics and anharmonic vibrational spectrum of TFA including overtone and combination vibrations. We also studied experimental photoisomerization and photodecomposition channels of HCOSH molecules with different wavelengths. We suggest that TFA is a potential sulfur containing candidate molecule for interstellar and planetary observations and discuss these in a light of different radiation e…
Photochemical behavior in azobenzene having acidic groups. Preparation of magnetic photoresponsive gels
2011
[EN] The photochemistry of three azobenzenes representing contrasting photochemical behaviors is described in the present work. Thus, Methyl Orange (MO, 4-[[(4-dimethylamino)phenyl]-azo]benzenesulfonic acid sodium salt, hereinafter (1) and 4-hydroxyazobenzene-4'-sulfonic acid (2) undergo in water fast photochemical proton shift, with decays in the microsecond timescale. In contrast to the previous cases, azobenzene-4,4'-dicarboxylic acid (3) undergoes photoisomerization in water. This photochemical behavior allows the preparation of aqueous gels with Aerosil as gelating agent (5% weight) exhibiting high cyclability and photoreversible isomerization of the trans to cis (300 nm irradiation) a…
Alkoxy substituted (E,E)-3,6-bis(styryl)pyridazine—a photosensitive mesogen for liquid crystals
2008
Abstract (E,E)-3,6-Bis(styryl)pyridazines (3a–t) bearing 2, 4 or 6 alkoxy chains were prepared by applying the Siegrist reaction of 3,6-dimethylpyridazine (13) and the corresponding azomethines 10a–t. The transversal dipole moment of these calamitic compounds effects an extremely high tendency for self-organization in thermotropic LC phases (N, SA, SB, SC, SE, SI/F, and Cub). The conjugated core structure represents moreover a chromophore with a high photosensitivity for (E,E)⇄(E,Z) isomerization reactions: this property makes the compounds interesting for optical imaging and switching techniques.
Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization
2000
In this paper we use ab initio multiconfigurational second-order perturbation theory to establish the intrinsic photoisomerization path model of retinal chromophores. This is accomplished by computing the ground state ( S 0 ) and the first two singlet excited-state ( S 1 , S 2 ) energies along the rigorously determined photoisomerization coordinate of the rhodopsin chromophore model 4- cis -γ-methylnona-2,4,6,8-tetraeniminium cation and the bacteriorhodopsin chromophore model all- trans -hepta-2,4,6-trieniminium cation in isolated conditions. The computed S 2 and S 1 energy profiles do not show any avoided crossing feature along the S 1 reaction path and maintain an energy gap >20 kcal⋅…
Trans-to-cis photoisomerization of cyclocurcumin in different environments rationalized by computational photochemistry
2020
International audience; Cyclocurcumin is a turmeric component that attracted much less attention compared to the well known curcumin. In spite of the less deep charcaterization of its properties, cyclocurcumin has shown promising anticancer effects when used in combination with curcumin. Especially, due to its peculiar molecular structure, cyclocurcumin can be regarded as an almost ideal photoswitch, whose capabilities can also be exploited for relevant biological applications. Here, by means of state-of-the-art computational methods for electronic excited-state calculations (TD-DFT, MS-CASPT2, XMS-CASPT2) we analyze in detail the absorption and photoisomerization pathways leading from the …
A NOT gate in a cis-trans photoisomerization model
2007
We numerically study the implementation of a NOT gate by laser pulses in a model molecular system presenting two electronic surfaces coupled by non adiabatic interactions. The two states of the bit are the fundamental states of the cis-trans isomers of the molecule. The gate is classical in the sense that it involves a one-qubit flip so that the encoding of the outputs is based on population analysis which does not take the phases into account. This gate can also be viewed as a double photo-switch process with the property that the same electric field controls the two isomerizations. As an example, we consider one-dimensional cuts in a model of the retinal in rhodopsin already proposed in t…
Effect of opsin on the shape of the potential energy surfaces at the conical intersection of the Rhodopsin chromophore
2008
Abstract In order to disentangle the role of the protein in the control of the photoisomerization of the chromophore of the visual pigment Rhodopsin, we compare the structure of the ground and excited potential energy surfaces of gas-phase and opsin-embedded 11- cis retinal chromophore at the corresponding (lowest energy) conical intersections. It is shown that, along the branching plane, the asymmetric opsin environment destabilizes one of the ground state relaxation channels emerging from the conical intersection. This suggests that opsin promotes the formation of the product (bathorhodopsin) via enhanced decay probability along the all- trans exit channel. In contrast, in the gas-phase n…
Photochemistry of Fluorinated Heterocyclic Compounds. An Expedient Route for the Synthesis of Fluorinated 1,3,4-Oxadiazoles and 1,2,4-Triazoles
2004
The photochemistry of some 3-N-alkylamino-5-perfluoroalkyl-1,2,4-oxadiazoles in the presence of nitrogen nucleophiles such as ammonia and primary and secondary aliphatic amines has been investigated. The primary photolytic intermediate from the cleavage of the ring O-N bond follows two distinct and competing pathways leading to (i). 5-perfluoroalkyl-1,3,4-oxadiazoles, through the ring contraction-ring expansion photoisomerization route favored by the presence of the base or (ii). 5-perfluoroalkyl-1,2,4-triazoles, through the intervention, as an internal nucleophile, of the exocyclic N-alkylamino moiety of the oxadiazole followed by the attack of the external nitrogen nucleophile and subsequ…
Conformational preferences and synthesis of isomers Z and E of oxazole-dehydrophenylalanine
2016
Dehydrophenylalanine, ΔPhe, is the most commonly studied α,β-dehydroamino acid. In nature, further modifications of the α,β-dehydroamino acids were found, for example, replacement of the C-terminal amide group by oxazole ring. The conformational properties of oxazole-dehydrophenylalanine residue (ΔPhe-Ozl), both isomers Z and E, were investigated. To determine all possible conformations, theoretical calculations were performed using Ac-(Z/E)-ΔPhe-Ozl(4-Me) model compounds at M06-2X/6-31++G(d,p) level of theory. Ac-(Z/E)-ΔPhe-Ozl-4-COOEt compounds were synthesized and the conformational preferences of each isomer, Z and E, were investigated using FTIR and NMR-NOE in solutions of increasing p…
Gelation of smectic liquid crystal phases with photosensitive gel forming agents.
2020
This paper studies the potential of 3 newly synthesized low molecular weight gelling agents (2 of them with azo groups) with the semicarbazide group as a H-bonding motif to gel the smectic phase of a commercial chiral smectic C material. To detect gelation two methods were used: the stabilization of the director pattern, which measures the interaction of the physical gel network with the LC-director, and the suppression of the onset of electrohydrodynamic instabilities, which measures the increase of viscosity. Special emphasis was put on the influence of the photochemical - isomerization of the gelling agents on gelation.From the stabilization of the director pattern an elastic component c…