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Theoretical and Computational and Experimental Advances on Molecular Optical Properties

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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 2023) | Viewed by 13144

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Dr. Heribert Reis

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Guest Editor

National Hellenic Research Foundation, Athens, Greece
Interests: nonlinear optical properties; computational chemistry; molecular motions; computational biomedicine; large-scale molecular dynamics simulations

Dr. Josep Maria Luis

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Guest Editor

Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, 17071 Girona, Spain
Interests: vibrational contributions to nonlinear optical properties; new DFT functionals for NLO; catalysis; reaction mechanisms; computational chemistry

Special Issue Information

Dear Colleagues,

The experimental determination and accurate theoretical calculation of molecular optical properties have become indispensable tools for the search of molecules with optimal properties tailored for modern optical applications.

Applications in information processing, optical sensors, electro-optical switches, light-emitting devices, solar cells, optical memories, and biophotonic applications depend on the availability of molecular materials with specifically optimized optical properties, such as radiative and nonradiative quantum yields, spectral signatures, multiphoton absorption and emission yields, optical nonlinearities, photoinduced nonadiabatic crossing mechanisms, photoacoustic properties, optical rotation, vibrational spectroscopies, etc. Significant advances in the experimental methodologies and the development of sophisticated methodologies for computation of the underlying microscopic processes, including intermolecular effects in macroscopic or nanoscopic materials, have been achieved in the last decades and are still an important target in current research.

This Special Issue aims to provide a forum for researchers to present current and recent developments in measurement and theoretical description of molecular optical properties. Original research papers, review articles and short communication letters are all welcome.

Dr. Heribert Reis
Dr. Josep Maria Luis
Guest Editors

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Keywords

radiative and nonradiative decay processes
multiphoton absorption and emission
nonadiabatic potential crossing
optical nonlinearities
photoacoustics
optical rotation
vibrational spectroscopies
solvent effects

Published Papers (10 papers)

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Research

21 pages, 12884 KiB

Open AccessArticle

Application of Inverse Design Approaches to the Discovery of Nonlinear Optical Switches

by Eline Desmedt, Léa Serrano Gimenez, Freija De Vleeschouwer and Mercedes Alonso

Molecules 2023, 28(21), 7371; https://doi.org/10.3390/molecules28217371 - 31 Oct 2023

Viewed by 1029

Abstract

Molecular switches, in which a stimulus induces a large and reversible change in molecular properties, are of significant interest in the domain of photonics. Due to their commutable redox states with distinct nonlinear optical (NLO) properties, hexaphyrins have emerged as a novel platform for multistate switches in nanoelectronics. In this study, we employ an inverse design algorithm to find functionalized 26R→28R redox switches with maximal

β_{H R S}

contrast. We focus on the role of core modifications, since a synergistic effect with meso-substitutions was recently found for the 30R-based switch. In contrast to these findings, the inverse design optima and subsequent database analysis of 26R-based switches confirm that core modifications are generally not favored when high NLO contrasts are targeted. Moreover, while push–pull combinations enhance the NLO contrast for both redox switches, they prefer a different arrangement in terms of electron-donating and electron-withdrawing functional groups. Finally, we aim at designing a three-state 26R→28R→ 30R switch with a similar NLO response for both ON states. Even though our best-performing three-state switch follows the design rules of the 30R-based component, our chemical compound space plots show that well-performing three-state switches can be found in regions shared by high-responsive 26R and 30R structures. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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27 pages, 3881 KiB

Open AccessArticle

Photoswitchable Molecular Units with Tunable Nonlinear Optical Activity: A Theoretical Investigation

by Aggelos Avramopoulos, Heribert Reis, Demeter Tzeli, Robert Zaleśny and Manthos G. Papadopoulos

Molecules 2023, 28(15), 5646; https://doi.org/10.3390/molecules28155646 - 26 Jul 2023

Cited by 1 | Viewed by 1155

Abstract

The first-, second-, and third-order molecular nonlinear optical properties, including two-photon absorption of a series of derivatives, involving two dithienylethene (DTE) groups connected by several molecular linkers (bis(ethylene-1,2-dithiolato)Ni- (NiBDT), naphthalene, quasilinear oligothiophene chains), are investigated by employing density functional theory (DFT). These properties can be efficiently controlled by DTE switches, in connection with light of appropriate frequency. NiBDT, as a linker, is associated with a greater contrast, in comparison to naphthalene, between the first and second hyperpolarizabilities of the “open–open” and the “closed–closed” isomers. This is explained by invoking the low-lying excited states of NiBDT. It is shown that the second hyperpolarizability can be used as an index, which follows the structural changes induced by photochromism. Assuming a Förster type transfer mechanism, the intramolecular excited-state energy transfer (EET) mechanism is studied. Two important parameters related to this are computed: the electronic coupling (V_DA) between the donor and acceptor fragments as well as the overlap between the absorption and emission spectra of the donor and acceptor groups. NiBDT as a linker is associated with a low electronic coupling, V_DA, value. We found that V_DA is affected by molecular geometry. Our results predict that the linker strongly influences the communication between the open–closed DTE groups. The sensitivity of the molecular nonlinear optical properties could assist with identification of molecular isomers. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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12 pages, 7752 KiB

Open AccessArticle

Theoretical Study on the Photoemission Performance of a Transmission Mode In_0.15Ga_0.85As Photocathode in the Near-Infrared Region

by Huan Wang, Jiajun Linghu, Pengfei Zou, Xuezhi Wang, Hao Shen and Bingru Hai

Molecules 2023, 28(13), 5262; https://doi.org/10.3390/molecules28135262 - 07 Jul 2023

Viewed by 796

Abstract

Benefiting from a high quantum efficiency, low thermal emittance, and large absorption coefficient, In_xGa_1−xAs is an excellent group III–V compound for negative electron affinity (NEA) photocathodes. As the emission layer, In_xGa_1−xAs, where x = 0.15, has the optimal performance for detection in the near-infrared (NIR) region. Herein, an NEA In_0.15Ga_0.85As photocathode with Al_0.63Ga_0.37As as the buffer layer is designed in the form of a transmission mode module. The electronic band structures and optical properties of In_0.15Ga_0.85As and Al_0.63Ga_0.37As are calculated based on density functional theory. The time response characteristics of the In_0.15Ga_0.85As photocathode have been fully investigated by changing the photoelectron diffusion coefficient, the interface recombination velocity, and the thickness of the emission layer. Our results demonstrate that the response time of the In_0.15Ga_0.85As photocathode can be reduced to 6.1 ps with an incident wavelength of 1064 nm. The quantum efficiency of the In_0.15Ga_0.85As photocathode is simulated by taking into account multilayer optical thin film theory. The results indicate that a high quantum efficiency can be obtained by parameter optimization of the emission layer. This paper provides significant theoretical support for the applications of semiconductor photocathodes in the near-infrared region, especially for the study of ultrafast responses in the photoemission process. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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21 pages, 5936 KiB

Open AccessArticle

Conformational Distributions of Phenyl β-D-Glucopyranoside and Gastrodin in Solution by Vibrational Optical Activity and Theoretical Calculations

by Mutasem Alshalalfeh, Ningjie Sun, Amanda Hanashiro Moraes, Alexandra Paola Aponte Utani and Yunjie Xu

Molecules 2023, 28(10), 4013; https://doi.org/10.3390/molecules28104013 - 10 May 2023

Cited by 1 | Viewed by 1401

Abstract

The conformational landscapes of two highly flexible monosaccharide derivatives, namely phenyl β-D-glucopyranoside (ph-β-glu) and 4-(hydroxymethyl)phenyl β-D-glucopyranoside, also commonly known as gastrodin, were explored using a combined experimental and theoretical approach. For the infrared, Raman, and the associated vibrational optical activity (VOA), i.e., vibrational circular dichroism and Raman optical activity, experiments of these two compounds in DMSO and in water were carried out. Extensive and systematic conformational searches were performed using a recently developed conformational searching tool called CREST (conformer-rotamer ensemble sampling tool) in the two solvents. Fourteen and twenty-four low-energy conformers were identified at the DFT level for ph-β-glu and gastrodin, respectively. The spectral simulations of individual conformers were done at the B3LYP-D3BJ/def2-TZVPD level with the polarizable continuum model of the solvents. The VOA spectral features exhibit much higher specificity to conformational differences than their parent infrared and Raman. The excellent agreements achieved between the experimental and simulated VOA spectra allow for the extraction of experimental conformational distributions of these two carbohydrates in solution directly. The experimental percentage abundances based on the hydroxymethyl (at the pyranose ring) conformations G+, G-, and T for ph-β-glu were obtained to be 15%, 75%, and 10% in DMSO and 53%, 40%, and 7% in water, respectively, in comparison to the previously reported gas phase values of 68%, 25%, and 7%, highlighting the important role of solvents in conformational preferences. The corresponding experimental distributions for gastrodin are 56%, 22%, and 22% in DMSO and 70%, 21%, and 9% in water. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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24 pages, 3693 KiB

Open AccessArticle

Non-Phenomenological Description of the Time-Resolved Emission in Solution with Quantum–Classical Vibronic Approaches—Application to Coumarin C153 in Methanol

by Javier Cerezo, Sheng Gao, Nicola Armaroli, Francesca Ingrosso, Giacomo Prampolini, Fabrizio Santoro, Barbara Ventura and Mariachiara Pastore

Molecules 2023, 28(9), 3910; https://doi.org/10.3390/molecules28093910 - 05 May 2023

Cited by 1 | Viewed by 1842

Abstract

We report a joint experimental and theoretical work on the steady-state spectroscopy and time-resolved emission of the coumarin C153 dye in methanol. The lowest energy excited state of this molecule is characterized by an intramolecular charge transfer thus leading to remarkable shifts of the time-resolved emission spectra, dictated by the methanol reorganization dynamics. We selected this system as a prototypical test case for the first application of a novel computational protocol aimed at the prediction of transient emission spectral shapes, including both vibronic and solvent effects, without applying any phenomenological broadening. It combines a recently developed quantum–classical approach, the adiabatic molecular dynamics generalized vertical Hessian method (Ad-MD

| g

VH), with nonequilibrium molecular dynamics simulations. For the steady-state spectra we show that the Ad-MD|gVH approach is able to reproduce quite accurately the spectral shapes and the Stokes shift, while a ∼0.15 eV error is found on the prediction of the solvent shift going from gas phase to methanol. The spectral shape of the time-resolved emission signals is, overall, well reproduced, although the simulated spectra are slightly too broad and asymmetric at low energies with respect to experiments. As far as the spectral shift is concerned, the calculated spectra from 4 ps to 100 ps are in excellent agreement with experiments, correctly predicting the end of the solvent reorganization after about 20 ps. On the other hand, before 4 ps solvent dynamics is predicted to be too fast in the simulations and, in the sub-ps timescale, the uncertainty due to the experimental time resolution (300 fs) makes the comparison less straightforward. Finally, analysis of the reorganization of the first solvation shell surrounding the excited solute, based on atomic radial distribution functions and orientational correlations, indicates a fast solvent response (≈100 fs) characterized by the strengthening of the carbonyl–methanol hydrogen bond interactions, followed by the solvent reorientation, occurring on the ps timescale, to maximize local dipolar interactions. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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22 pages, 8398 KiB

Open AccessArticle

The Resonance Raman Spectrum of Cytosine in Water: Analysis of the Effect of Specific Solute–Solvent Interactions and Non-Adiabatic Couplings

by Qiushuang Xu, Yanli Liu, Meishan Wang, Javier Cerezo, Roberto Improta and Fabrizio Santoro

Molecules 2023, 28(5), 2286; https://doi.org/10.3390/molecules28052286 - 01 Mar 2023

Cited by 1 | Viewed by 1669

Abstract

In this contribution, we report a computational study of the vibrational Resonance Raman (vRR) spectra of cytosine in water, on the grounds of potential energy surfaces (PES) computed by time-dependent density functional theory (TD-DFT) and CAM-B3LYP and PBE0 functionals. Cytosine is interesting because it is characterized by several close-lying and coupled electronic states, challenging the approach commonly used to compute the vRR for systems where the excitation frequency is in quasi-resonance with a single state. We adopt two recently developed time-dependent approaches, based either on quantum dynamical numerical propagations of vibronic wavepackets on coupled PES or on analytical correlation functions for cases in which inter-state couplings were neglected. In this way, we compute the vRR spectra, considering the quasi-resonance with the eight lowest-energy excited states, disentangling the role of their inter-state couplings from the mere interference of their different contributions to the transition polarizability. We show that these effects are only moderate in the excitation energy range explored by experiments, where the spectral patterns can be rationalized from the simple analysis of displacements of the equilibrium positions along the different states. Conversely, at higher energies, interference and inter-state couplings play a major role, and the adoption of a fully non-adiabatic approach is strongly recommended. We also investigate the effect of specific solute–solvent interactions on the vRR spectra, by considering a cluster of cytosine, hydrogen-bonded by six water molecules, and embedded in a polarizable continuum. We show that their inclusion remarkably improves the agreement with the experiments, mainly altering the composition of the normal modes, in terms of internal valence coordinates. We also document cases, mostly for low-frequency modes, in which a cluster model is not sufficient, and more elaborate mixed quantum classical approaches, in explicit solvent models, need to be applied. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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12 pages, 2324 KiB

Open AccessArticle

Theoretical Study on Non-Linear Optics Properties of Polycyclic Aromatic Hydrocarbons and the Effect of Their Intercalation with Carbon Nanotubes

by Imane Khelladi, Michael Springborg, Ali Rahmouni, Redouane Chadli and Majda Sekkal-Rahal

Molecules 2023, 28(1), 110; https://doi.org/10.3390/molecules28010110 - 23 Dec 2022

Cited by 1 | Viewed by 1144

Abstract

Results of a theoretical study devoted to comparing NLO (non-linear optics) responses of derivatives of tetracene, isochrysene, and pyrene are reported. The static hyperpolarizability β, the dipole moment μ, the HOMO and LUMO orbitals, and their energy gap were calculated using the CAM-B3LYP density functional combined with the cc-pVDZ basis set. The para-disubstituted NO₂-tetracene-N(CH₃)₂ has the highest NLO response, which is related to a large intramolecular charge transfer. Adding vinyl groups to the para-disubstituted NO₂-tetracene-N(CH₃)₂ results in an increase in the NLO responses. We further investigated the effect of the intercalation of various push–pull molecules inside an armchair single-walled carbon nanotube. The intercalation leads to increased NLO responses, something that depends critically on the position of the guest molecule and/or on functionalization of the nanotube by donor and attractor groups. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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8 pages, 352 KiB

Open AccessArticle

HeH⁺ under Spatial Confinement

by Marta Chołuj, Paweł Lipkowski and Wojciech Bartkowiak

Molecules 2022, 27(24), 8997; https://doi.org/10.3390/molecules27248997 - 16 Dec 2022

Viewed by 1116

Abstract

In the present study, the influence of spatial confinement on the bond length as well as dipole moment, polarizability and (hyper)polarizabilities of HeH

^{+}

ion was analyzed. The effect of spatial confinement was modelled by cylindrically symmetric harmonic oscillator potential, that can be [...] Read more.

In the present study, the influence of spatial confinement on the bond length as well as dipole moment, polarizability and (hyper)polarizabilities of HeH

^{+}

ion was analyzed. The effect of spatial confinement was modelled by cylindrically symmetric harmonic oscillator potential, that can be used to mimic high pressure conditions. Based on the conducted research it was found that the spatial confinement significantly affects the investigated properties. Increasing the confinement strength leads to a substantial decrease of their values. This work may be of particular interest for astrochemistry as HeH

^{+}

is believed to be the first compound to form in the Universe. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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18 pages, 624 KiB

Open AccessArticle

Hyperpolarizabilities of Push–Pull Chromophores in Solution: Interplay between Electronic and Vibrational Contributions

by Tomáš Hrivnák, Miroslav Medveď, Wojciech Bartkowiak and Robert Zaleśny

Molecules 2022, 27(24), 8738; https://doi.org/10.3390/molecules27248738 - 09 Dec 2022

Cited by 2 | Viewed by 1166

Abstract

Contemporary design of new organic non-linear optical (NLO) materials relies to a large extent on the understanding of molecular and electronic structure–property relationships revealed during the years by available computational approaches. The progress in theory—hand-in-hand with experiment—has enabled us to identify and analyze various physical aspects affecting the NLO responses, such as the environmental effects, molecular vibrations, frequency dispersion, and system dynamics. Although it is nowadays possible to reliably address these effects separately, the studies analyzing their mutual interplay are still very limited. Here, we employ density functional theory (DFT) methods in combination with an implicit solvent model to examine the solvent effects on the electronic and harmonic as well as anharmonic vibrational contributions to the static first hyperpolarizability of a series of push–pull

α

ω

-diphenylpolyene oligomers, which were experimentally shown to exhibit notable second-order NLO responses. We demonstrate that the magnitudes of both vibrational and electronic contributions being comparable in the gas phase significantly increase in solvents, and the enhancement can be, in some cases, as large as three- or even four-fold. The electrical and mechanical anharmonic contributions are not negligible but cancel each other out to a large extent. The computed dynamic solute NLO properties of the studied systems are shown to be in a fair agreement with those derived from experimentally measured electric-field-induced second-harmonic generation (EFISHG) signals. Our results substantiate the necessity to consider concomitantly both solvation and vibrational effects in modeling static NLO properties of solvated systems. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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10 pages, 2476 KiB

Open AccessArticle

Spectroelectrochemical and Theoretical Study of [Si(ttpy)₂](PF₆)₄: A Potential Polychromatic Electrochromic Dye

by Derek M. Peloquin, Askhat N. Bimukhanov, Anuar A. Aldongarov, Jon W. Merkert, Bernadette T. Donovan-Merkert and Thomas A. Schmedake

Molecules 2022, 27(23), 8521; https://doi.org/10.3390/molecules27238521 - 03 Dec 2022

Cited by 1 | Viewed by 1074

Abstract

Complexes consisting of earth-abundant main group metals such as silicon with polypyridine ligands are of interest for a variety of optical and electronic applications including as electrochromic colorants. Previous spectroelectrochemical studies with tris(2,2′-bipyridyl)silicon(IV) hexafluorophosphate, [Si(bpy)₃](PF₆)_4, demonstrated an ability to control the color saturation of the potential electrochromic dye, with the intensity of the dye’s green color increasing as the charge state sequentially reduces from 4+ to 1+. In this study, the synthesis of bis(4′-(4-tolyl)-2,2′:6′,2″-terpyridine)silicon(IV) hexafluorophosphate, [Si(ttpy)₂](PF₆)₄, is reported along with electrochemical and spectroelectrochemical analyses. Computational modeling (density functional theory) is used to further elucidate the electrochromic properties of previously reported Si(bpy)₃ⁿ⁺ species and the new Si(ttpy)₂ⁿ⁺ species. While the homoleptic tris(bidentate)silicon(IV) complexes are attractive as electrochromic dyes for tunable color saturation, the bis(tridentate)silicon(IV) complexes are attractive as polychromatic electrochromic dyes. Full article

(This article belongs to the Special Issue Theoretical and Computational and Experimental Advances on Molecular Optical Properties)

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