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Photophysics and Photochemistry in Complex Molecular Systems

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

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 36074

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Special Issue Editors

Dr. Juan J. Nogueira

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Guest Editor

Talento-CAM Fellow, Department of Chemistry, Faculty of Science and IADCHEM (Institute for Advanced Research in Chemistry), Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, Calle Francisco Tomás y Valiente, 7, 28049 Madrid, Spain
Interests: DNA and lipid membrane damage; photochemistry; biological modeling; computational chemistry; quantum chemistry; molecular dynamics; QM/MM

Dr. Lara Martínez-Fernández

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Department of Chemistry, Faculty of Science and IADCHEM (Institute for Advanced Research in Chemistry), Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, Calle Francisco Tomás y Valiente, 7, 28049 Madrid, Spain
Interests: photoinduced processes in DNA: photophysics, photochemistry, photoionization, photodamage; DNA derivatives, excited states, spectroscopy

Dr. Javier Segarra-Marti

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Guest Editor

Instituto de Ciencia Molecular, Universitat de Valencia, P. O. Box 22085, 46071 Valencia, Spain
Interests: CASSCF/CASPT2; conical intersections; DNA photophysics; theoretical photochemistry; electronic spectroscopy; multidimensional spectroscopy; photoionisation

Special Issue Information

Dear Colleagues,

Photophysics and photochemistry are broad disciplines that study light–matter interactions. This covers a range of topics from the formation of DNA damage to light-induced charge separation and energy transfer featured in all sorts of modern molecular materials and applications. Indeed, the study of such phenomena underpins many of the advances made in diverse fields such as renewable energy, new material design, and medicine.

This Special Issue covers all aspects related to light-induced processes in complex molecular systems investigated by early-career scientists worldwide. Specific interests include the simulation of photoinduced phenomena by quantum mechanical calculations and non-adiabatic molecular dynamics, as well as time-resolved experimental spectroscopic characterizations in organic, inorganic, and biological molecular systems. This broadly spans physical chemistry processes across the atto- to nanosecond timescales in terms of both modeling and experiments. The published original work is aimed at showcasing recent important advances made by early-career scientists in the fields of photophysics and photochemistry.

Dr. Juan José Nogueira Pérez
Dr. Lara Martínez-Fernández
Dr. Javier Segarra-Marti
Guest Editors

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Keywords

Molecular photochemistry
Non-linear spectroscopy
Internal conversion
Intersystem crossing
Transition metal complexes
UV absorption and emission
Charge transfer processes
Energy transfer processes

Published Papers (14 papers)

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Research

12 pages, 2503 KiB

Open AccessArticle

A Quinoxaline−Naphthaldehyde Conjugate for Colorimetric Determination of Copper Ion

by Sutapa Sahu, Yeasin Sikdar, Riya Bag, Michael G. B. Drew, José P. Cerón-Carrasco and Sanchita Goswami

Molecules 2022, 27(9), 2908; https://doi.org/10.3390/molecules27092908 - 3 May 2022

Cited by 5 | Viewed by 1808

Abstract

This work facilitates detection of bivalent copper ion by a simple Schiff base probe QNH based on a quinoxaline−naphthaldehyde framework. The detailed study in absorption spectroscopy and theoretical aspects and crystal study of the probe and probe−copper complex has been discussed. The detection limit of the probe in the presence of Cu²⁺ is 0.45 µM in HEPES−buffer/acetonitrile (3/7, v/v) medium for absorption study. The reversibility of the probe−copper complex has been investigated by EDTA. The selective visual detection of copper has been established also in gel form. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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15 pages, 7513 KiB

Open AccessArticle

Turn on Fluorescence Sensing of Zn²⁺ Based on Fused Isoindole-Imidazole Scaffold

by Sutapa Sahu, Yeasin Sikdar, Riya Bag, Javier Cerezo, José P. Cerón-Carrasco and Sanchita Goswami

Molecules 2022, 27(9), 2859; https://doi.org/10.3390/molecules27092859 - 30 Apr 2022

Cited by 10 | Viewed by 1794

Abstract

Optical chemosensors caused a revolution in the field of sensing due to their high specificity, sensitivity, and fast detection features. Imidazole derivatives have offered promising features in the literature as they bear suitable donor/acceptor groups for the selective analytes in the skeleton. In this work, an isoindole-imidazole containing a Schiff base chemosensor (1-{3-[(2-Diethylamino-ethylimino)-methyl]-2-hydroxy-5-methyl-phenyl}-2H-imidazo[5,1-a]isoindole-3,5-dione) was designed and synthesized. The complete sensing phenomena have been investigated by means of UV-Vis, fluorescence, lifetime measurement, FT-IR, NMR and ESI-MS spectroscopic techniques. The optical properties of the synthesized ligand were investigated in 3:7 HEPES buffer:DMSO medium and found to be highly selective and sensitive toward Zn²⁺ ion through a fluorescence turn-on response with detection limit of 0.073 μm. Furthermore, this response is effective in gel form also. The competition studies reveal that the response of the probe for Zn²⁺ ion is unaffected by other relevant metal ions. The stoichiometric binding study was performed utilizing Job’s method which indicated a 1:1 sensor–Zn²⁺ ensemble. Computational calculations were performed to pinpoint the mechanism of sensing. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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10 pages, 1668 KiB

Open AccessArticle

Ultrafast Excited-State Decay Mechanisms of 6-Thioguanine Followed by Sub-20 fs UV Transient Absorption Spectroscopy

by Danielle C. Teles-Ferreira, Cristian Manzoni, Lara Martínez-Fernández, Giulio Cerullo, Ana Maria de Paula and Rocío Borrego-Varillas

Molecules 2022, 27(4), 1200; https://doi.org/10.3390/molecules27041200 - 10 Feb 2022

Cited by 5 | Viewed by 2133

Abstract

Understanding the primary steps following UV photoexcitation in sulphur-substituted DNA bases (thiobases) is fundamental for developing new phototherapeutic drugs. However, the investigation of the excited-state dynamics in sub-100 fs time scales has been elusive until now due to technical challenges. Here, we track the ultrafast decay mechanisms that lead to the electron trapping in the triplet manifold for 6-thioguanine in an aqueous solution, using broadband transient absorption spectroscopy with a sub-20 fs temporal resolution. We obtain experimental evidence of the fast internal conversion from the S₂(ππ*) to the S₁(nπ*) states, which takes place in about 80 fs and demonstrates that the S₁(nπ*) state acts as a doorway to the triplet population in 522 fs. Our results are supported by MS-CASPT2 calculations, predicting a planar S₂(ππ*) pseudo-minimum in agreement with the stimulated emission signal observed in the experiment. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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15 pages, 3466 KiB

Open AccessArticle

Molecular Identification of the Transient Species Mediating the Deactivation Dynamics of Solvated Guanosine and Deazaguanosine

by Javier Ortín-Fernández, Jesús González-Vázquez, Lara Martínez-Fernández and Inés Corral

Molecules 2022, 27(3), 989; https://doi.org/10.3390/molecules27030989 - 1 Feb 2022

Cited by 3 | Viewed by 1639

Abstract

Small structural alterations of the purine/pyrimidine core have been related to important photophysical changes, such as the loss of photostability. Similarly to canonical nucleobases, solute-solvent interactions can lead to a change in the excited state lifetimes and/or to the interplay of different states in the photophysics of these modified nucleobases. To shed light on both effects, we here report a complete picture of the absorption spectra and excited state deactivation of deoxyguanosine and its closely related derivative, deoxydeazaguanosine, in water and methanol through the mapping of the excited state potential energy surfaces and molecular dynamics simulations at the TD-DFT level of theory. We show that the N by CH exchange in the imidazole ring of deoxyguanosine translates into a small red-shift of the bright states and slightly faster dynamics. In contrast, changing solvent from water to methanol implies the opposite, i.e., that the deactivation of both systems to the ground state is significantly hindered. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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12 pages, 6283 KiB

Open AccessArticle

Emission Quenching in Tetraphenylfuran Crystal: Why This Propeller-Shaped Molecule Does Not Emit in the Condensed Phase

by Ljiljana Stojanović and Rachel Crespo-Otero

Molecules 2022, 27(2), 522; https://doi.org/10.3390/molecules27020522 - 14 Jan 2022

Cited by 3 | Viewed by 2328

Abstract

Due to their substantial fluorescence quantum yields in the crystalline phase, propeller-shaped molecules have recently gained significant attention as potential emissive materials for optoelectronic applications. For the family of cyclopentadiene derivatives, light-emission is highly dependent on the nature of heteroatomic substitutions. In this paper, we investigate excited state relaxation pathways in the tetraphenyl-furan molecule (TPF), which in contrast with other molecules in the family, shows emission quenching in the solid-state. For the singlet manifold, our calculations show nonradiative pathways associated with C-O elongation are blocked in both vacuum and the solid state. A fraction of the population can be transferred to the triplet manifold and, subsequently, to the ground state in both phases. This process is expected to be relatively slow due to the small spin-orbit couplings between the relevant singlet-triplet states. Emission quenching in crystalline TPF seems to be in line with more efficient exciton hopping rates. Our simulations help clarify the role of conical intersections, population of the triplet states and crystalline structure in the emissive response of propeller-shaped molecules. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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12 pages, 2988 KiB

Open AccessArticle

The Impact of Retinal Configuration on the Protein–Chromophore Interactions in Bistable Jumping Spider Rhodopsin-1

by Jonathan R. Church, Jógvan Magnus Haugaard Olsen and Igor Schapiro

Molecules 2022, 27(1), 71; https://doi.org/10.3390/molecules27010071 - 23 Dec 2021

Cited by 9 | Viewed by 4091

Abstract

Bistable rhodopsins have two stable forms that can be interconverted by light. Due to their ability to act as photoswitches, these proteins are considered as ideal candidates for applications such as optogenetics. In this work, we analyze a recently crystalized bistable rhodopsin, namely the jumping spider rhodopsin-1 (JSR1). This rhodopsin exhibits identical absorption maxima for the parent and the photoproduct form, which impedes its broad application. We performed hybrid QM/MM simulations to study three isomers of the retinal chromophore: the 9-cis, 11-cis and all-trans configurations. The main aim was to gain insight into the specific interactions of each isomer and their impact on the absorption maximum in JSR1. The absorption spectra were computed using sampled snapshots from QM/MM molecular dynamics trajectories and compared to their experimental counterparts. The chromophore–protein interactions were analyzed by visualizing the electrostatic potential of the protein and projecting it onto the chromophore. It was found that the distance between a nearby tyrosine (Y126) residue plays a larger role in the predicted absorption maximum than the primary counterion (E194). Geometric differences between the isomers were also noted, including a structural change in the polyene chain of the chromophore, as well as changes in the nearby hydrogen bonding network. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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31 pages, 2451 KiB

Open AccessArticle

Analyzing Grid-Based Direct Quantum Molecular Dynamics Using Non-Linear Dimensionality Reduction

by Gareth W. Richings and Scott Habershon

Molecules 2021, 26(24), 7418; https://doi.org/10.3390/molecules26247418 - 7 Dec 2021

Cited by 2 | Viewed by 2113

Abstract

Grid-based schemes for simulating quantum dynamics, such as the multi-configuration time-dependent Hartree (MCTDH) method, provide highly accurate predictions of the coupled nuclear and electronic dynamics in molecular systems. Such approaches provide a multi-dimensional, time-dependent view of the system wavefunction represented on a coordinate grid; in the case of non-adiabatic simulations, additional information about the state populations adds a further layer of complexity. As such, wavepacket motion on potential energy surfaces which couple many nuclear and electronic degrees-of-freedom can be extremely challenging to analyse in order to extract physical insight beyond the usual expectation-value picture. Here, we show that non-linear dimensionality reduction (NLDR) methods, notably diffusion maps, can be adapted to extract information from grid-based wavefunction dynamics simulations, providing insight into key nuclear motions which explain the observed dynamics. This approach is demonstrated for 2-D and 9-D models of proton transfer in salicylaldimine, as well as 8-D and full 12-D simulations of cis-trans isomerization in ethene; these simulations demonstrate how NLDR can provide alternative views of wavefunction dynamics, and also highlight future developments. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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19 pages, 2998 KiB

Open AccessArticle

E/Z Molecular Photoswitches Activated by Two-Photon Absorption: Comparison between Different Families

by Marco Marazzi, Cristina García-Iriepa, Carlos Benitez-Martin, Francisco Najera, Antonio Monari and Diego Sampedro

Molecules 2021, 26(23), 7379; https://doi.org/10.3390/molecules26237379 - 5 Dec 2021

Cited by 7 | Viewed by 2878

Abstract

Nonlinear optical techniques as two-photon absorption (TPA) have raised relevant interest within the last years due to the capability to excite chromophores with photons of wavelength equal to only half of the corresponding one-photon absorption energy. At the same time, its probability being proportional to the square of the light source intensity, it allows a better spatial control of the light-induced phenomenon. Although a consistent number of experimental studies focus on increasing the TPA cross section, very few of them are devoted to the study of photochemical phenomena induced by TPA. Here, we show a design strategy to find suitable E/Z photoswitches that can be activated by TPA. A theoretical approach is followed to predict the TPA cross sections related to different excited states of various photoswitches’ families, finally concluding that protonated Schiff-bases (retinal)-like photoswitches outperform compared to the others. The donor-acceptor substitution effect is therefore rationalized for the successful TPA activatable photoswitch, in order to maximize its properties, finally also forecasting a possible application in optogenetics. Some experimental measurements are also carried out to support our conclusions. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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20 pages, 1616 KiB

Open AccessArticle

Micro-Solvated DMABN: Excited State Quantum Dynamics and Dual Fluorescence Spectra

by Sandra Gómez, Esra N. Soysal and Graham A. Worth

Molecules 2021, 26(23), 7247; https://doi.org/10.3390/molecules26237247 - 29 Nov 2021

Cited by 5 | Viewed by 2832

Abstract

In this work, we report a complete analysis by theoretical and spectroscopic methods of the short-time behaviour of 4-(dimethylamino)benzonitrile (DMABN) in the gas phase as well as in cyclohexane, tetrahydrofuran, acetonitrile, and water solution, after excitation to the L

_{a}

state. The spectroscopic [...] Read more.

_{a}

state. The spectroscopic properties of DMABN were investigated experimentally using UV absorption and fluorescence emission spectroscopy. The computational study was developed at different electronic structure levels and using the Polarisable Continuum Model (PCM) and explicit solvent molecules to reproduce the solvent environment. Additionally, excited state quantum dynamics simulations in the diabatic picture using the direct dynamics variational multiconfigurational Gaussian (DD-vMCG) method were performed, the largest quantum dynamics “on-the-fly” simulations performed with this method until now. The comparison with fully converged multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) dynamics on parametrised linear vibronic coupling (LVC) potentials show very similar population decays and evolution of the nuclear wavepacket. The ring C=C stretching and three methyl tilting modes are identified as the responsible motions for the internal conversion from the L

_{a}

to the L

_{b}

states. No major differences are observed in the ultrafast initial decay in different solvents, but we show that this effect depends strongly on the level of electronic structure used. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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12 pages, 1998 KiB

Open AccessArticle

Photochemistry of Thymine in Protic Polar Nanomeric Droplets Using Electrostatic Embeding TD-DFT/MM

by Miquel Huix-Rotllant

Molecules 2021, 26(19), 6021; https://doi.org/10.3390/molecules26196021 - 4 Oct 2021

Cited by 1 | Viewed by 1936

Abstract

Thymine photochemistry is important for understanding DNA photodamage. In the gas phase, thymine undergoes a fast non-radiative decay from S

_{2}

to S

_{1}

. In the S

_{1}

state, it gets trapped for several picoseconds until returning to the ground-state S

_{0}

[...] Read more.

Thymine photochemistry is important for understanding DNA photodamage. In the gas phase, thymine undergoes a fast non-radiative decay from S

_{2}

to S

_{1}

. In the S

_{1}

state, it gets trapped for several picoseconds until returning to the ground-state S

_{0}

. Here, we explore the electrostatic effects of nanomeric droplets of methanol and water on the excited states of thymine. For this purpose, we develop and implement an electrostatic embedding TD-DFT/MM method based on a QM/MM coupling defined through electrostatic potential fitting charges. We show that both in methanol and water, the mechanism is similar to the gas phase. The solvent molecules participate in defining the branching plane of S

_{0}

_{1}

intersection and have a negligible effect on the S

_{1}

_{2}

intersection. Despite the wrong topology of the ground/excited state intersections, electrostatic embedding TD-DFT/MM allows for a fast exploration of the potential energy surfaces and a qualitative picture of the photophysics of thymine in solvent droplets. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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10 pages, 1553 KiB

Open AccessArticle

Exploiting Complex Fluorophore Interactions to Monitor Virus Capsid Disassembly

by Swarupa Chatterjee, Bram A. Schotpoort, Thieme Elbert, Jeroen J. L. M. Cornelissen, Mireille M. A. E. Claessens and Christian Blum

Molecules 2021, 26(19), 5750; https://doi.org/10.3390/molecules26195750 - 22 Sep 2021

Cited by 3 | Viewed by 2541

Abstract

Supramolecular protein complexes are the corner stone of biological processes; they are essential for many biological functions. Unraveling the interactions responsible for the (dis)assembly of these complexes is required to understand nature and to exploit such systems in future applications. Virus capsids are well-defined assemblies of hundreds of proteins and form the outer shell of non-enveloped viruses. Due to their potential as a drug carriers or nano-reactors and the need for virus inactivation strategies, assessing the intactness of virus capsids is of great interest. Current methods to evaluate the (dis)assembly of these protein assemblies are experimentally demanding in terms of instrumentation, expertise and time. Here we investigate a new strategy to monitor the disassembly of fluorescently labeled virus capsids. To monitor surfactant-induced capsid disassembly, we exploit the complex photophysical interplay between multiple fluorophores conjugated to capsid proteins. The disassembly of the capsid changes the photophysical interactions between the fluorophores, and this can be spectrally monitored. The presented data show that this low complexity method can be used to study and monitor the disassembly of supramolecular protein complexes like virus capsids. However, the range of labeling densities that is suitable for this assay is surprisingly narrow. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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13 pages, 3750 KiB

Open AccessArticle

Photophysical Deactivation Mechanisms of the Pyrimidine Analogue 1-Cyclohexyluracil

by Danillo Valverde, Adalberto V. S. de Araújo and Antonio Carlos Borin

Molecules 2021, 26(17), 5191; https://doi.org/10.3390/molecules26175191 - 27 Aug 2021

Cited by 5 | Viewed by 2267

Abstract

The photophysical relaxation mechanisms of 1-cyclohexyluracil, in vacuum and water, were investigated by employing the Multi-State CASPT2 (MS-CASPT2, Multi-State Complete Active-Space Second-Order Perturbation Theory) quantum chemical method and Dunning’s cc-pVDZ basis sets. In both environments, our results suggest that the primary photophysical event [...] Read more.

S_{1}

^{1} (π π^{*})

bright state. Afterwards, two likely deactivation pathways can take place, which is sustained by linear interpolation in internal coordinates defined via Z-Matrix scans connecting the most important characteristic points. The first one (Route 1) is the same relaxation mechanism observed for uracil, its canonical analogue, i.e., internal conversion to the ground state through an ethylenic-like conical intersection. The other route (Route 2) is the direct population transfer from the

S_{1}

^{1} (π π^{*})

bright state to the

T_{2}

^{3} (n π^{*})

triplet state via an intersystem crossing process involving the (

S_{1}

^{1} (π π^{*})

T_{2}

^{3} (n π^{*})

)

_{S T C P}

singlet-triplet crossing point. As the spin-orbit coupling is not too large in either environment, we propose that most of the electronic population initially on the

S_{1}

^{1} (π π^{*})

state returns to the ground following the same ultrafast deactivation mechanism observed in uracil (Route 1), while a smaller percentage goes to the triplet manifold. The presence of a minimum on the

S_{1}

^{1} (π π^{*})

potential energy hypersurface in water can help to understand why experimentally it is noticed suppression of the triplet states population in polar protic solvent. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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16 pages, 26785 KiB

Open AccessArticle

“On-The-Fly” Non-Adiabatic Dynamics Simulations on Photoinduced Ring-Closing Reaction of a Nucleoside-Based Diarylethene Photoswitch

by Dong-Hui Xu, Laicai Li, Xiang-Yang Liu and Ganglong Cui

Molecules 2021, 26(9), 2724; https://doi.org/10.3390/molecules26092724 - 6 May 2021

Cited by 5 | Viewed by 2959

Abstract

Nucleoside-based diarylethenes are emerging as an especial class of photochromic compounds that have potential applications in regulating biological systems using noninvasive light with high spatio-temporal resolution. However, relevant microscopic photochromic mechanisms at atomic level of these novel diarylethenes remain to be explored. Herein, we have employed static electronic structure calculations (MS-CASPT2//M06-2X, MS-CASPT2//SA-CASSCF) in combination with non-adiabatic dynamics simulations to explore the related photoinduced ring-closing reaction of a typical nucleoside-based diarylethene photoswitch, namely, PS-IV. Upon excitation with UV light, the open form PS-IV can be excited to a spectroscopically bright S₁ state. After that, the molecule relaxes to the conical intersection region within 150 fs according to the barrierless relaxed scan of the C1–C6 bond, which is followed by an immediate deactivation to the ground state. The conical intersection structure is very similar to the ground state transition state structure which connects the open and closed forms of PS-IV, and therefore plays a crucial role in the photochromism of PS-IV. Besides, after analyzing the hopping structures, we conclude that the ring closing reaction cannot complete in the S₁ state alone since all the C1–C6 distances of the hopping structures are larger than 2.00 Å. Once hopping to the ground state, the molecules either return to the original open form of PS-IV or produce the closed form of PS-IV within 100 fs, and the ring closing quantum yield is estimated to be 56%. Our present work not only elucidates the ultrafast photoinduced pericyclic reaction of the nucleoside-based diarylethene PS-IV, but can also be helpful for the future design of novel nucleoside-based diarylethenes with better performance. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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34 pages, 10917 KiB

Open AccessArticle

Solution and Solid-State Photophysical Properties of Positional Isomeric Acrylonitrile Derivatives with Core Pyridine and Phenyl Moieties: Experimental and DFT Studies

by Armando Castillo, Paulina Ceballos, Pilar Santos, Margarita Cerón, Perumal Venkatesan, Enrique Pérez-Gutiérrez, Martha Sosa-Rivadeneyra, Subbiah Thamotharan, Maxime A. Siegler and María Judith Percino

Molecules 2021, 26(6), 1500; https://doi.org/10.3390/molecules26061500 - 10 Mar 2021

Cited by 6 | Viewed by 2483

Abstract

The compounds I (Z)-2-(phenyl)-3-(2,4,5-trimethoxyphenyl)acrylonitrile with one side (2,4,5-MeO-), one symmetrical (2Z,2′Z)-2,2′-(1,4-phenylene)bis(3-(2,4,5-trimethoxyphenyl)acrylonitrile), II (both sides with (2,4,5-MeO-), and three positional isomers with pyridine (Z)-2-(pyridin-2- 3, or 4-yl)-3-(2,4,5-trimethoxyphenyl)acrylonitrile, III–V were synthetized and characterized by UV-Vis, fluorescence, IR, H¹-NMR, and EI mass spectrometry as well as single crystal X-ray diffraction (SCXRD). The optical properties were strongly influenced by the solvent (hyperchromic and hypochromic shift), which were compared with the solid state. According to the solvatochromism theory, the excited-state (μ_e) and ground-state (μ_g) dipole moments were calculated based on the variation of Stokes shift with the solvent’s relative permittivity, refractive index, and polarity parameters. SCXRD analyses revealed that the compounds I and II crystallized in the monoclinic system with the space group, P2₁/n and P2₁/c, respectively, and with Z = 4 and 2. III, IV, and V crystallized in space groups: orthorhombic, Pbca; triclinic, P-1; and monoclinic, P2₁ with Z = 1, 2, and 2, respectively. The intermolecular interactions for compounds I–V were investigated using the CCDC Mercury software and their energies were quantified using PIXEL. The density of states (DOS), molecular electrostatic potential surfaces (MEPS), and natural bond orbitals (NBO) of the compounds were determined to evaluate the photophysical properties. Full article

(This article belongs to the Special Issue Photophysics and Photochemistry in Complex Molecular Systems)

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