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New Studies of Photoisomerization

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (30 April 2020) | Viewed by 20203

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Prof. Dr. Martial Boggio-Pasqua

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Guest Editor

Universite de Toulouse, Toulouse, France
Interests: theoretical chemistry; excited states; dynamics; photochemistry; photochromism

Special Issue Information

Dear Colleagues,

Photoisomerization, which is the photochemical process resulting in a change of isomer, is a very common response upon light irradiation of photoactive molecular systems. It can involve different types of molecular reorganization such as bond rotation, skeletal rearrangements or atom- or group-transfer. Typical examples are cis-trans photoisomerizations, photoinduced cycloadditions, electrocyclic reactions and tautomerizations. Photoisomerization is the primary photochemical reaction of chromophores in several biological photoreceptors. The most prominent example is the cis-trans photoisomerization of the retinal chromophore in rhodopsin which is the primary photochemical event involved in vision. Photoisomerization is often associated with changes in physical and chemical properties of the molecular system: Along with the geometrical rearrangement, it may be accompanied by spectral changes, change of refractive index, dielectric constant, dipole moment, oxidation/reduction potential. This light-activated process is in most cases completely reversible, and the molecules can be switched back and forth between two or more isomeric forms, providing what is commonly known as photoswitches. Photoisomerizable molecules have entered the new generation of innovative functional materials with high added value. Applications are already widespread in nanosciences, biology, and photonic or optoelectronic devices. For example, they have been exploited to develop various technological devices such as sensors, actuators, information storage and processing and high-resolution imaging techniques.

A variety of synthetic photoswitches, that can undergo a reversible change in their structure upon irradiation with light, have been designed. The vast majority of these compounds rely on organic molecules. Among the main groups of compounds that have found numerous applications as switching molecules, one can cite azobenzenes, stilbenes, dihydroazulenes, diarylethenes, spiropyrans and spirooxazines, naphthopyrans, fulgides, fulgimides, and related compounds. Transition metal complexes have also been designed to display photoisomerizable capabilities. These systems are often based on linkage isomerizations between the metal center, and various ambidentate ligands (e.g., sulfoxide, sulfur dioxide, nitrosyl). The advantage of using such inorganic systems lies in the large flexibility available to tune the photoisomerizable properties with the use of different ligands.

This forthcoming Special Issue of Molecules entitled “New Studies of Photoisomerization” will be devoted to photoisomerizable compounds, collecting original contributions both from experimental and theoretical studies.

Prof. Martial Boggio-Pasqua
Guest Editor

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Keywords

photoswitches
photochromism
synthesis
molecular design
optical properties
time-resolved spectroscopy
computational photochemistry
photodynamics

Published Papers (7 papers)

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Research

20 pages, 5178 KiB

Open AccessArticle

Effect of a =X-NH-Fragment, (X = C, N), on Z/E Isomerization and ON/OFF Functionality of Isatin Arylhydrazones, ((Arylamino)Methylene)Indolin-2-Ones and Their Anions

by Pavol Tisovský, Klaudia Csicsai, Jana Donovalová, Róbert Šandrik, Róbert Sokolík and Anton Gáplovský

Molecules 2020, 25(13), 3082; https://doi.org/10.3390/molecules25133082 - 06 Jul 2020

Cited by 8 | Viewed by 2394

Abstract

The subject of this work was the study of thermally and photochemically stimulated Z ↔ E isomerization and hydrazo ↔ azo tautomerism of Z- and E-isomers of isatin arylhydrazones and ((arylamino)methylene)indolin-2-ones and their anions. Using NMR, UV-Vis spectroscopy, kinetic measurements, and HPLC, we studied the relationship of structure, (Z- and E-isomers), of these compounds and hydrazo=azo tautomerism. The ON/OFF functionality of these compounds and their anions using light to stimulate switching between ON and OFF states was investigated. We pointed out the characterization of the effect of =N- and =CH- structural fragments and aryl structure on ON and OFF states of isatin arylhydrazones and ((arylamino)methylene)indolin-2-ones. Full article

(This article belongs to the Special Issue New Studies of Photoisomerization)

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16 pages, 4570 KiB

Open AccessFeature PaperArticle

Computational and Crystallographic Examination of Naphthoquinone Based Diarylethene Photochromes

by Dinesh G. Patel, Martial Boggio-Pasqua, Travis B. Mitchell, Ian M. Walton, William R. Quigley and Frank A. Novak

Molecules 2020, 25(11), 2630; https://doi.org/10.3390/molecules25112630 - 05 Jun 2020

Cited by 2 | Viewed by 2942

Abstract

Photochromic compounds have a lengthy history of study and a profusion of applications that stand to gain from these studies. Among the classes of photochromic compounds, diarylethenes show desirable properties including high fatigue resistance and thermal stability, thus meeting some of the most important criteria necessary to enter the realm of practical applications. Recently, photochromic diarylethenes containing quinone functionalities have demonstrated interesting optical and solid-state properties. When properly interfaced with suitable electron withdrawing groups on the aryl component, both the ring-opening and ring-closing reactions can be achieved with visible light; this is in contrast to most other diarylethenes where UV light is required for ring closure. Unfortunately, quantitative conversion from open to closed forms is not possible. In this work, we examine the relative energies of conformations of solid-state structures observed by X-ray crystallography and evaluate their thermal stabilities based on density functional theory (DFT) calculations. Time-dependent DFT (TD–DFT) is used to model the UV-vis absorption spectra of these quinone diarylethenes. We show that spectral overlap between open and closed forms is a major hindrance to full photoconversion. Full article

(This article belongs to the Special Issue New Studies of Photoisomerization)

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11 pages, 2286 KiB

Open AccessArticle

CASPT2 Potential Energy Curves for NO Dissociation in a Ruthenium Nitrosyl Complex

by Francesco Talotta, Leticia González and Martial Boggio-Pasqua

Molecules 2020, 25(11), 2613; https://doi.org/10.3390/molecules25112613 - 04 Jun 2020

Cited by 18 | Viewed by 3056

Abstract

Ruthenium nitrosyl complexes are fascinating photoactive compounds showing complex photoreactivity, such as N→O linkage photoisomerism and NO photorelease. This dual photochemical behavior has been the subject of many experimental studies in order to optimize these systems for applications as photoswitches or therapeutic agents for NO delivery. However, despite recent experimental and computational studies along this line, the underlying photochemical mechanisms still need to be elucidated for a more efficient design of these systems. Here, we present a theoretical contribution based on the calculations of excited-state potential energy profiles for NO dissociation in the prototype trans-[RuCl(NO)(py)₄]²⁺ complex at the complete active space second-order perturbation theory (CASPT2). The results point to a sequential two-step photon absorption photorelease mechanism coupled to partial photoisomerization to a side-on intermediate, in agreement with previous density functional theory calculations. Full article

(This article belongs to the Special Issue New Studies of Photoisomerization)

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15 pages, 1758 KiB

Open AccessArticle

Photorelaxation Pathways of 4-(N,N-Dimethylamino)-4′-nitrostilbene Upon S₁ Excitation Revealed by Conical Intersection and Intersystem Crossing Networks

by Ziyue He, Ruidi Xue, Yibo Lei, Le Yu and Chaoyuan Zhu

Molecules 2020, 25(9), 2230; https://doi.org/10.3390/molecules25092230 - 09 May 2020

Cited by 2 | Viewed by 2728

Abstract

Multi-state n-electron valence state second order perturbation theory (MS-NEVPT2) was utilized to reveal the photorelaxation pathways of 4-(N,N-dimethylamino)-4′-nitrostilbene (DANS) upon S₁ excitation. Within the interwoven networks of five S₁/S₀ and three T₂/T₁ conical intersections (CIs), and three S₁/T₂, one S₁/T₁ and one S₀/T₁ intersystem crossings (ISCs), those competing nonadiabatic decay pathways play different roles in trans-to-cis and cis-to-trans processes, respectively. After being excited to the Franck–Condon (FC) region of the S₁ state, trans-S₁-FC firstly encounters an ultrafast conversion to quinoid form. Subsequently, the relaxation mainly proceeds along the triplet pathway, trans-S₁-FC → ISC-S₁/T₂-trans → CI-T₂/T₁-trans → ISC-S₀/T₁-twist → trans- or cis-S₀. The singlet relaxation pathway mediated by CI-S₁/S₀-twist-c is hindered by the prominent energy barrier on S₁ surface and by the reason that CI-S₁/S₀-trans and CI-S₁/S₀-twist-t are both not energetically accessible upon S₁ excitation. On the other hand, the cis-S₁-FC lies at the top of steeply decreasing potential energy surfaces (PESs) towards the CI-S₁/S₀-twist-c and CI-S₁/S₀-DHP regions; therefore, the initial twisting directions of DN and DAP moieties determine the branching ratio between α_C=C twisting (cis-S₁-FC → CI-S₁/S₀-twist-c → trans- or cis-S₀) and DHP formation relaxation pathways (cis-S₁-FC → CI-S₁/S₀-DHP → DHP-S₀) on the S₁ surface. Moreover, the DHP formation could also take place via the triplet relaxation pathway, cis-S₁-FC → ISC-S₁/T₁-cis → DHP-T₁ → DHP-S₀, however, which may be hindered by insufficient spin-orbit coupling (SOC) strength. The other triplet pathways for cis-S₁-FC mediated by ISC-S₁/T₂-cis are negligible due to the energy or geometry incompatibility of possible consecutive stepwise S₁ → T₂ → T₁ or S₁ → T₂ → S₁ processes. The present study reveals photoisomerization dynamic pathways via conical intersection and intersystem crossing networks and provides nice physical insight into experimental investigation of DANS. Full article

(This article belongs to the Special Issue New Studies of Photoisomerization)

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19 pages, 2186 KiB

Open AccessArticle

Multistep Photochemical Reactions of Polypyridine-Based Ruthenium Nitrosyl Complexes in Dimethylsulfoxide

by Nataliia Marchenko, Pascal G. Lacroix, Valerii Bukhanko, Marine Tassé, Carine Duhayon, Martial Boggio-Pasqua and Isabelle Malfant

Molecules 2020, 25(9), 2205; https://doi.org/10.3390/molecules25092205 - 08 May 2020

Cited by 13 | Viewed by 2407

Abstract

The photorelease of nitric oxide (NO·) has been investigated in dimethylsulfoxide (DMSO) on two compounds of formula [Ru(R-tpy)(bpy)(NO)](PF₆)₃, in which bpy stands for 2,2′-bipyridine and R-tpy for the 4′-R-2,2′:6′,2″-terpyridine with R = H and MeOPh. It is observed that both complexes are extremely sensitive to traces of water, leading to an equilibrium between [Ru(NO)] and [Ru(NO₂)]. The photoproducts of formula [Ru(R-tpy)(bpy)(DMSO)](PF₆)₂ are further subjected to a photoreaction leading to a reversible linkage isomerization between the stable Ru-DMSO_(S) (sulfur linked) and the metastable Ru-DMSO_(O) (oxygen linked) species. A set of 4 [Ru(R-tpy)(bpy)(DMSO)]²⁺ complexes (R = H, MeOPh, BrPh, NO₂Ph) is investigated to characterize the ratio and mechanism of the isomerization which is tentatively related to the difference in absorbance between the Ru-DMSO_(S) and Ru-DMSO_(O) forms. In addition, the X-ray crystal structures of [Ru(tpy)(bpy)(NO)](PF₆)₃ and [Ru(MeOPh-tpy)(bpy)(DMSO_(S))](PF₆)₂ are presented. Full article

(This article belongs to the Special Issue New Studies of Photoisomerization)

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13 pages, 2014 KiB

Open AccessArticle

Ultrafast Backbone Protonation in Channelrhodopsin-1 Captured by Polarization Resolved Fs Vis-pump—IR-Probe Spectroscopy and Computational Methods

by Till Stensitzki, Suliman Adam, Ramona Schlesinger, Igor Schapiro and Karsten Heyne

Molecules 2020, 25(4), 848; https://doi.org/10.3390/molecules25040848 - 14 Feb 2020

Cited by 7 | Viewed by 3045

Abstract

Channelrhodopsins (ChR) are light-gated ion-channels heavily used in optogenetics. Upon light excitation an ultrafast all-trans to 13-cis isomerization of the retinal chromophore takes place. It is still uncertain by what means this reaction leads to further protein changes and channel conductivity. Channelrhodopsin-1 in Chlamydomonas augustae exhibits a 100 fs photoisomerization and a protonated counterion complex. By polarization resolved ultrafast spectroscopy in the mid-IR we show that the initial reaction of the retinal is accompanied by changes in the protein backbone and ultrafast protonation changes at the counterion complex comprising Asp299 and Glu169. In combination with homology modelling and quantum mechanics/molecular mechanics (QM/MM) geometry optimization we assign the protonation dynamics to ultrafast deprotonation of Glu169, and transient protonation of the Glu169 backbone, followed by a proton transfer from the backbone to the carboxylate group of Asp299 on a timescale of tens of picoseconds. The second proton transfer is not related to retinal dynamics and reflects pure protein changes in the first photoproduct. We assume these protein dynamics to be the first steps in a cascade of protein-wide changes resulting in channel conductivity. Full article

(This article belongs to the Special Issue New Studies of Photoisomerization)

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13 pages, 3275 KiB

Open AccessArticle

Mechanosynthesis of Photochromic Oligophenyleneimines: Optical, Electrochemical and Theoretical Studies

by Miguel Angel Amado-Briseño, Luis Ángel Zárate-Hernández, Karina Alemán-Ayala, Oscar Coreño Alonso, Julián Cruz-Borbolla, José Manuel Vásquez-Pérez, Víctor Esteban Reyes-Cruz, María Aurora Veloz-Rodríguez, Esteban Rueda-Soriano, Thangarasu Pandiyan and Rosa Angeles Vázquez-García

Molecules 2019, 24(5), 849; https://doi.org/10.3390/molecules24050849 - 28 Feb 2019

Cited by 10 | Viewed by 2772

Abstract

In this work, two oligophenyleneimines type pentamers with terminal aldehydes, designated as DAFCHO (4,4′-((((((2,5-bis(octyloxy)-1,4-phenylene)bis(methanylylidene))bis(azanyl ylidene))bis(9H-fluorene-7,2-diyl))bis(azanylylidene))bis(methanylylidene))bis(2,5-bis(octyloxy) benzaldehyde)) and FDACHO (4,4′-((((((2,5-bis(octyloxy)-1,4-phenylene)bis(methanylylidene))bis (azanylylidene))bis(4,1-phenylene))bis(azanylylidene))bis(methanylylidene))bis(2,5-bis(octyloxy) benzaldehyde)) were synthesized by mechanochemistry method using 2,5-bis(octyloxy) terephtal aldehyde and 2,7-diaminofluorene or 1,4-phenylenediamine. All compounds were spectroscopically characterized using ¹H and ¹³C-NMR, FT-IR and mass spectrometry MALDITOF. The optical properties of the compounds were analyzed by UV-vis spectroscopy using different solvents. We observed that DAFCHO and FDACHO exhibit interesting photochromic properties when they are dissolved in chloroform and exposed to sunlight for 3, 5 and 10 min. The value of the energy band gap was calculated from the absorption spectra without irradiation E_gap(optical). It was 2.50 eV for DAFCHO in chloroform solution, and it decreased to 2.34 eV when it is in films. For FDACHO, it was 2.41 eV in solution and 2.27 eV in film. HOMO (Highest Occupied Molecular Orbital), LUMO (Lowest Unoccupied Molecular Orbital) and E_{gap(electrochemical)} values were obtained by electrochemical studies. The results indicate that the compounds can be considered as organic semiconductors since their values are 2.35 eV for DAFCHO and 2.06 eV for FDACHO. The structural and electronic properties of the compounds were corroborated with a DFT (Density Functional Theory) study. Full article

(This article belongs to the Special Issue New Studies of Photoisomerization)

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