Research

13 pages, 2664 KiB

Open AccessArticle

Solution and Solid-State Optical Properties of Trifluoromethylated 5-(Alkyl/aryl/heteroaryl)-2-methyl-pyrazolo[1,5-a]pyrimidine System

by Felipe S. Stefanello, Jean C. B. Vieira, Juliane N. Araújo, Vitória B. Souza, Clarissa P. Frizzo, Marcos A. P. Martins, Nilo Zanatta, Bernardo A. Iglesias and Helio G. Bonacorso

Photochem 2022, 2(2), 345-357; https://doi.org/10.3390/photochem2020024 - 19 May 2022

Cited by 4 | Viewed by 1683

Abstract

This paper describes the photophysical properties of a series of seven selected examples of 5-(alkyl/aryl/heteroaryl)-2-methyl-7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidines (3), which contain alkyl, aryl, and heteroaryl substituents attached to the scaffolds of 3. Given the electron-donor groups and -withdrawing groups, the optical [...] Read more.

This paper describes the photophysical properties of a series of seven selected examples of 5-(alkyl/aryl/heteroaryl)-2-methyl-7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidines (3), which contain alkyl, aryl, and heteroaryl substituents attached to the scaffolds of 3. Given the electron-donor groups and -withdrawing groups, the optical absorption and emission in the solid state and solution showed interesting results. Absorption UV–Vis and fluorescence properties in several solvents of a pyrazolo[1,5-a]pyrimidines series were investigated, and all derivatives were absorbed in the ultraviolet region despite presenting higher quantum emission fluorescence yields in solution and moderate emission in the solid state. Moreover, the solid-state thermal stability of compounds 3a–g was assessed using thermogravimetric analysis. The thermal decomposition profile showed a single step with almost 100% mass loss for all compounds 3. Additionally, the values of T_0.05 are considerably low (72–187 °C), especially for compound 3a (72 °C), indicating low thermal stability for this series of pyrazolo[1,5-a]pyrimidines. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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19 pages, 3342 KiB

Open AccessArticle

Electronic Absorption, Emission, and Two-Photon Absorption Properties of Some Extended 2,4,6-Triphenyl-1,3,5-Triazines

by Alison G. Barnes, Nicolas Richy, Anissa Amar, Mireille Blanchard-Desce, Abdou Boucekkine, Olivier Mongin and Frédéric Paul

Photochem 2022, 2(2), 326-344; https://doi.org/10.3390/photochem2020023 - 19 May 2022

Viewed by 2284

Abstract

We report herein the linear optical properties of some extended 2,4,6-triphenyl-s-triazines of formula 2,4,6-[(1,4-C₆H₄)C≡C(4-C₆H₄X)]₃-1,3,5-(C₃H₃N₃) (3-X; X = NO₂, CN, OMe, NMe₂, [...] Read more.

We report herein the linear optical properties of some extended 2,4,6-triphenyl-s-triazines of formula 2,4,6-[(1,4-C₆H₄)C≡C(4-C₆H₄X)]₃-1,3,5-(C₃H₃N₃) (3-X; X = NO₂, CN, OMe, NMe₂, NPh₂) and related analogues 4 and 7-X (X = H, NPh₂), before briefly discussing their two-photon absorption (2PA) cross-sections. Their 2PA performance is discussed in relation to 2PA values previously measured for closely related octupoles such as N,N′,N″-triphenylisocyanurates (1-X, 5, and 6-X) or 1,3,5-triphenylbenzenes (2-X). While s-triazines are usually much better two-photon absorbers in the near-IR range than these molecules, especially when functionalised by electron-releasing substituents at their periphery, they present a decreased transparency window in the visible range due to their red-shifted first 1PA peak, in particular when compared with corresponding isocyanurates analogues. In contrast, due to their significantly larger two-photon brilliancy, 2,4,6-triphenyl-s-triazines appear more promising than the latter for two-photon fluorescence bio-imaging purposes. Rationalisation of these unexpected outcomes is proposed based on DFT calculations. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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11 pages, 1353 KiB

Open AccessArticle

Mono-, Di-, Tri-Pyrene Substituted Cyclic Triimidazole: A Family of Highly Emissive and RTP Chromophores

by Daniele Malpicci, Clelia Giannini, Elena Lucenti, Alessandra Forni, Daniele Marinotto and Elena Cariati

Photochem 2021, 1(3), 477-487; https://doi.org/10.3390/photochem1030031 - 18 Nov 2021

Cited by 7 | Viewed by 2329

Abstract

The search of new organic emitters is receiving a strong motivation by the development of ORTP materials. In the present study we report on the preparation, optical and photophysical characterization, by both steady state and time resolved techniques, of two pyrene-functionalized cyclic triimidazole [...] Read more.

The search of new organic emitters is receiving a strong motivation by the development of ORTP materials. In the present study we report on the preparation, optical and photophysical characterization, by both steady state and time resolved techniques, of two pyrene-functionalized cyclic triimidazole derivatives. Together with the already reported mono-substituted derivative, the di- and tri-substituted members of the family have revealed as intriguing emitters characterized by impressive quantum yields in solution and RTP properties in the solid state. In particular, phosphorescence lifetimes increase from 5.19 to 20.54 and 40.62 ms for mono-, di- and trisubstituted compounds, respectively. Based on spectroscopical results and theoretical DFT/TDDFT calculations on the di-pyrene molecule, differences in photophysical performances of the three compounds have been assigned to intermolecular interactions increasing with the number of pyrene moieties appended to the cyclic triimidazole scaffold. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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15 pages, 3809 KiB

Open AccessArticle

Photocatalytic Reduction of CO₂ over Iron-Modified g-C₃N₄ Photocatalysts

by Miroslava Edelmannová, Martin Reli, Kamila Kočí, Ilias Papailias, Nadia Todorova, Tatiana Giannakopoulou, Panagiotis Dallas, Eamonn Devlin, Nikolaos Ioannidis and Christos Trapalis

Photochem 2021, 1(3), 462-476; https://doi.org/10.3390/photochem1030030 - 13 Nov 2021

Cited by 4 | Viewed by 2567

Abstract

Pure g-C₃N₄ sample was prepared by thermal treatment of melamine at 520 °C, and iron-modified samples (0.1, 0.3 and 1.1 wt.%) were prepared by mixing g-C₃N₄ with iron nitrate and calcination at 520 °C. The photocatalytic activity [...] Read more.

Pure g-C₃N₄ sample was prepared by thermal treatment of melamine at 520 °C, and iron-modified samples (0.1, 0.3 and 1.1 wt.%) were prepared by mixing g-C₃N₄ with iron nitrate and calcination at 520 °C. The photocatalytic activity of the prepared materials was investigated based on the photocatalytic reduction of CO₂, which was conducted in a homemade batch reactor that had been irradiated from the top using a 365 nm Hg lamp. The photocatalyst with the lowest amount of iron ions exhibited an extraordinary methane and hydrogen evolution in comparison with the pure g-C₃N₄ and g-C₃N₄ with higher iron amounts. A higher amount of iron ions was not a beneficial for CO₂ photoreduction because the iron ions consumed too many photogenerated electrons and generated hydroxyl radicals, which oxidized organic products from the CO₂ reduction. It is clear that there are numerous reactions that occur simultaneously during the photocatalytic process, with several of them competing with CO₂ reduction. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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16 pages, 2953 KiB

Open AccessArticle

Modelling Photoionisations in Tautomeric DNA Nucleobase Derivatives 7H-Adenine and 7H-Guanine: Ultrafast Decay and Photostability

by Javier Segarra-Martí, Sara M. Nouri and Michael J. Bearpark

Photochem 2021, 1(2), 287-301; https://doi.org/10.3390/photochem1020018 - 10 Sep 2021

Cited by 5 | Viewed by 2347

Abstract

The study of radiation effects in DNA is a multidisciplinary endeavour, connecting the physical, chemical and biological sciences. Despite being mostly filtered by the ozone layer, sunlight radiation is still expected to (photo)ionise DNA in sizeable yields, triggering an electron removal process and [...] Read more.

The study of radiation effects in DNA is a multidisciplinary endeavour, connecting the physical, chemical and biological sciences. Despite being mostly filtered by the ozone layer, sunlight radiation is still expected to (photo)ionise DNA in sizeable yields, triggering an electron removal process and the formation of potentially reactive cationic species. In this manuscript, photoionisation decay channels of important DNA tautomeric derivatives, 7H-adenine and 7H-guanine, are characterised with accurate CASSCF/XMS-CASPT2 theoretical methods. These simulation techniques place the onset of ionisation for 7H-adenine and 7H-guanine on average at 8.98 and 8.43 eV, in line with recorded experimental evidence when available. Cationic excited state decays are analysed next, uncovering effective barrierless deactivation routes for both species that are expected to decay to their (cationic) ground state on ultrafast timescales. Conical intersection topographies reveal that these photoionisation processes are facilitated by sloped single-path crossings, known to foster photostability, and which are predicted to enable the (VUV) photo-protection mechanisms present in these DNA tautomeric species. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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19 pages, 4711 KiB

Open AccessArticle

Spectral Optical Properties of Rabbit Brain Cortex between 200 and 1000 nm

by Tânia M. Gonçalves, Inês S. Martins, Hugo F. Silva, Valery V. Tuchin and Luís M. Oliveira

Photochem 2021, 1(2), 190-208; https://doi.org/10.3390/photochem1020011 - 11 Aug 2021

Cited by 13 | Viewed by 2453

Abstract

The knowledge of the optical properties of biological tissues in a wide spectral range is highly important for the development of noninvasive diagnostic or treatment procedures. The absorption coefficient is one of those properties, from which various information about tissue components can be [...] Read more.

The knowledge of the optical properties of biological tissues in a wide spectral range is highly important for the development of noninvasive diagnostic or treatment procedures. The absorption coefficient is one of those properties, from which various information about tissue components can be retrieved. Using transmittance and reflectance spectral measurements acquired from ex vivo rabbit brain cortex samples allowed to calculate its optical properties in the ultraviolet to the near infrared spectral range. Melanin and lipofuscin, the two pigments that are related to the aging of tissues and cells were identified in the cortex absorption. By subtracting the absorption of these pigments from the absorption of the brain cortex, it was possible to evaluate the true ratios for the DNA/RNA and hemoglobin bands in the cortex—12.33-fold (at 260 nm), 12.02-fold (at 411 nm) and 4.47-fold (at 555 nm). Since melanin and lipofuscin accumulation increases with the aging of the brain tissues and are related to the degeneration of neurons and their death, further studies should be performed to evaluate the evolution of pigment accumulation in the brain, so that new optical methods can be developed to aid in the diagnosis and monitoring of brain diseases. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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23 pages, 6794 KiB

Open AccessArticle

Panchromatic Copper Complexes for Visible Light Photopolymerization

by Alexandre Mau, Guillaume Noirbent, Céline Dietlin, Bernadette Graff, Didier Gigmes, Frédéric Dumur and Jacques Lalevée

Photochem 2021, 1(2), 167-189; https://doi.org/10.3390/photochem1020010 - 04 Aug 2021

Cited by 21 | Viewed by 2499

Abstract

In this work, eleven heteroleptic copper complexes were designed and studied as photoinitiators of polymerization in three-component photoinitiating systems in combination with an iodonium salt and an amine. Notably, ten of them exhibited panchromatic behavior and could be used for long wavelengths. Ferrocene-free [...] Read more.

In this work, eleven heteroleptic copper complexes were designed and studied as photoinitiators of polymerization in three-component photoinitiating systems in combination with an iodonium salt and an amine. Notably, ten of them exhibited panchromatic behavior and could be used for long wavelengths. Ferrocene-free copper complexes were capable of efficiently initiating both the radical and cationic polymerizations and exhibited similar performances to that of the benchmark G1 system. Formation of acrylate/epoxy IPNs was also successfully performed even upon irradiation at 455 nm or at 530 nm. Interestingly, all copper complexes containing the 1,1′-bis(diphenylphosphino)ferrocene ligand were not photoluminescent, evidencing that ferrocene could efficiently quench the photoluminescence properties of copper complexes. Besides, these ferrocene-based complexes were capable of efficiently initiating free radical polymerization processes. The ferrocene moiety introduced in the different copper complexes affected neither their panchromatic behaviors nor their abilities to initiate free radical polymerizations. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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15 pages, 11609 KiB

Open AccessArticle

Enhanced Photoluminescence of Electrodeposited Europium Complex on Bare and Terpyridine-Functionalized Porous Si Surfaces

by Min Hee Joo, So Jeong Park, Hye Ji Jang, Sung-Min Hong, Choong Kyun Rhee and Youngku Sohn

Photochem 2021, 1(1), 38-52; https://doi.org/10.3390/photochem1010004 - 06 Apr 2021

Cited by 4 | Viewed by 2300

Abstract

The trivalent Eu(III) ion exhibits unique red luminescence and plays an significant role in the display industry. Herein, the amperometry electrodeposition method was employed to electrodeposit Eu(III) materials on porous Si and terpyridine-functionalized Si surfaces. The electrodeposited materials were fully characterized by scanning [...] Read more.

The trivalent Eu(III) ion exhibits unique red luminescence and plays an significant role in the display industry. Herein, the amperometry electrodeposition method was employed to electrodeposit Eu(III) materials on porous Si and terpyridine-functionalized Si surfaces. The electrodeposited materials were fully characterized by scanning electron microscopy, X-ray diffraction crystallography, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Photoluminescence (PL) spectroscopy revealed that PL signals were substantially increased upon deposition on porous Si surfaces. PL signals were mainly due to direct excitation and charge-transfer-indirect excitations before and after thermal annealing, respectively. The as-electrodeposited materials were of a Eu(III) complex consisting of OH, H₂O, NO₃⁻, and CO₃²⁻ groups. The complex was transformed to Eu₂O₃ upon thermal annealing at 700 °C. The electrodeposition on porous surfaces provide invaluable information on the fabrication of thin films for displays, as well as photoelectrodes for catalyst applications. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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12 pages, 1247 KiB

Open AccessArticle

Photoprotective Properties of Eumelanin: Computational Insights into the Photophysics of a Catechol:Quinone Heterodimer Model System

by Victoria C. Frederick, Thomas A. Ashy, Barbara Marchetti, Michael N. R. Ashfold and Tolga N. V. Karsili

Photochem 2021, 1(1), 26-37; https://doi.org/10.3390/photochem1010003 - 10 Mar 2021

Viewed by 2743

Abstract

Melanins are skin-centered molecular structures that block harmful UV radiation from the sun and help protect chromosomal DNA from UV damage. Understanding the photodynamics of the chromophores that make up eumelanin is therefore paramount. This manuscript presents a multi-reference computational study of the [...] Read more.

Melanins are skin-centered molecular structures that block harmful UV radiation from the sun and help protect chromosomal DNA from UV damage. Understanding the photodynamics of the chromophores that make up eumelanin is therefore paramount. This manuscript presents a multi-reference computational study of the mechanisms responsible for the experimentally observed photostability of a melanin-relevant model heterodimer comprising a catechol (C)–benzoquinone (Q) pair. The present results validate a recently proposed photoinduced intermolecular transfer of an H atom from an OH moiety of C to a carbonyl-oxygen atom of the Q. Photoexcitation of the ground state C:Q heterodimer (which has a π-stacked “sandwich” structure) results in population of a locally excited ππ* state (on Q), which develops increasing charge-transfer (biradical) character as it evolves to a “hinged” minimum energy geometry and drives proton transfer (i.e., net H atom transfer) from C to Q. The study provides further insights into excited state decay mechanisms that could contribute to the photostability afforded by the bulk polymeric structure of eumelanin. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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16 pages, 1841 KiB

Open AccessFeature PaperArticle

Infrared Spectrum and UV-Induced Photochemistry of Matrix-Isolated Phenyl 1-Hydroxy-2-Naphthoate

by İsa Sıdır, Sándor Góbi, Yadigar Gülseven Sıdır and Rui Fausto

Photochem 2021, 1(1), 10-25; https://doi.org/10.3390/photochem1010002 - 26 Feb 2021

Viewed by 2178

Abstract

The conformational stability, infrared spectrum, and photochemistry of phenyl 1-hydroxy-2-naphthoate (PHN) were studied by matrix isolation infrared spectroscopy and theoretical computations performed at the DFT(B3LYP)/6-311++G(d,p) level of theory. The main intramolecular interactions determining the relative stability of seven conformers of the molecule were [...] Read more.

The conformational stability, infrared spectrum, and photochemistry of phenyl 1-hydroxy-2-naphthoate (PHN) were studied by matrix isolation infrared spectroscopy and theoretical computations performed at the DFT(B3LYP)/6-311++G(d,p) level of theory. The main intramolecular interactions determining the relative stability of seven conformers of the molecule were evaluated. According to the calculations, the twofold degenerated O–H···O=C intramolecularly hydrogen-bonded conformer with the phenyl ring ester group ±68.8° out of the plane of the substituted naphtyl moiety is the most stable conformer of the molecule. This conformer is considerably more stable than the second most stable form (by ~15 kJ mol⁻¹), in which a weaker O–H···O–C intramolecular hydrogen bond exists. The compound was isolated in cryogenic argon and N₂ matrices, and the conformational composition in the matrices was investigated by infrared spectroscopy. In agreement with the predicted relative energies of the conformers, the analysis of the spectra indicated that only the most stable conformer of PHN was present in the as-deposited matrices. The matrices were then irradiated at various wavelengths by narrowband tunable UV light within the 331.7–235.0 nm wavelength range. This resulted in the photodecarbonylation of PHN, yielding 2-phenoxynaphthalen-1-ol, together with CO. The extension of the decarbonylation was found to depend on the excitation wavelength. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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Review

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23 pages, 5931 KiB

Open AccessReview

A Photochemical Overview of Molecular Solar Thermal Energy Storage

by Alberto Gimenez-Gomez, Lucien Magson, Beatriz Peñin, Nil Sanosa, Jacobo Soilán, Raúl Losantos and Diego Sampedro

Photochem 2022, 2(3), 694-716; https://doi.org/10.3390/photochem2030045 - 22 Aug 2022

Cited by 5 | Viewed by 2809

Abstract

The design of molecular solar fuels is challenging because of the long list of requirements these molecules have to fulfil: storage density, solar harvesting capacity, robustness, and heat release ability. All of these features cause a paradoxical design due to the conflicting effects [...] Read more.

The design of molecular solar fuels is challenging because of the long list of requirements these molecules have to fulfil: storage density, solar harvesting capacity, robustness, and heat release ability. All of these features cause a paradoxical design due to the conflicting effects found when trying to improve any of these properties. In this contribution, we will review different types of compounds previously suggested for this application. Each of them present several advantages and disadvantages, and the scientific community is still struggling to find the ideal candidate suitable for practical applications. The most promising results have been found using norbornadiene-based systems, although the use of other alternatives like azobenzene or dihydroazulene cannot be discarded. In this review, we primarily focus on highlighting the optical and photochemical aspects of these three families, discussing the recently proposed systems and recent advances in the field. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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Other

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15 pages, 2745 KiB

Open AccessPerspective

Photochemistry of Metal Nitroprussides: State-of-the-Art and Perspectives

by Paula M. Crespo, Oscar F. Odio and Edilso Reguera

Photochem 2022, 2(2), 390-404; https://doi.org/10.3390/photochem2020027 - 31 May 2022

Cited by 2 | Viewed by 2121

Abstract

This contribution summarizes the current state in the photochemistry of metal nitroprussides, which is dominated by the electronic structure of the nitrosyl group. From the combination of p orbitals of the nitrogen and oxygen atoms in the NO⁺ ligand, a π*NO molecular [...] Read more.

This contribution summarizes the current state in the photochemistry of metal nitroprussides, which is dominated by the electronic structure of the nitrosyl group. From the combination of p orbitals of the nitrogen and oxygen atoms in the NO⁺ ligand, a π*NO molecular orbital of relatively low energy is formed, which has π*_2px and π*_2py character. This is a double degenerate orbital. When the nitrosyl group is found coordinated to the iron atom in the nitroprusside ion, the availability of that low energy π*NO orbital results in light-induced electronic transitions from the iron atom d_xy, d_xz and d_yz orbitals, 2b₂ (xy) → 7e (π*NO) and 6e (xz,yz) → 7e (π*NO), which are observed at 498 and 394 nm, respectively. These light-induced transitions and the possibility of NO isomer formation dominate the photochemistry of metal nitroprussides. In this feature paper, we discuss the implications of such transitions in the stability of coordination compounds based on the nitroprusside ion in the presence of water molecules for both 3D and 2D structures, including the involved degradation mechanisms. These photo-induced electronic transitions modify the physical and functional properties of solids where the nitroprusside ion forms part of their structure and appear as an opportunity for tuning their magnetic, electrical, optical and as energy-applied materials, for instance. This contribution illustrates these opportunities with results from some recently reported studies, and possible research subjects, even some not explored, are mentioned. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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