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Photochem, Volume 4, Issue 1 (March 2024) – 8 articles

Cover Story (view full-size image): Ultrafast pump–probe spectroscopic studies allow for deep insights into the mechanisms and timescales of photophysical and photochemical processes. Extracting valuable information from these studies, such as reactive intermediates’ lifetimes and coherent oscillation frequencies, is an example of the inverse problems of chemical kinetics. This study provides explicit details on how and why these parameters should be properly fitting in pump–probe spectroscopy. View this paper
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13 pages, 1579 KiB  
Article
Torsional Disorder in Tetraphenyl [3]-Cumulenes: Insight into Excited State Quenching
by David Bain, Julia Chang, Yihuan Lai, Thomas Khazanov, Phillip J. Milner and Andrew J. Musser
Photochem 2024, 4(1), 138-150; https://0-doi-org.brum.beds.ac.uk/10.3390/photochem4010008 - 9 Feb 2024
Viewed by 1029
Abstract
Cumulenes are linear molecules consisting of consecutive double bonds linking chains of sp-hybridized carbon atoms. They have primarily been of interest for potential use as molecular wires or in other nanoscale electronic devices, but more recently, other applications such as catalysis or even [...] Read more.
Cumulenes are linear molecules consisting of consecutive double bonds linking chains of sp-hybridized carbon atoms. They have primarily been of interest for potential use as molecular wires or in other nanoscale electronic devices, but more recently, other applications such as catalysis or even light harvesting through singlet fission have been speculated. Despite the recent theoretical and experimental interest, the photoexcitation of cumulenes typically results in quenching on the picosecond timescale, and the exact quenching mechanism for even the simplest of [3]-cumulenes lacks a clear explanation. In this report, we perform transient absorption spectroscopy on a set of model [3]-cumulene derivatives in a wide range of environmental conditions to demonstrate that the planarization of phenyl groups ultimately quenches the excited state. By restricting this intramolecular motion, we increase the excited state lifetime by a few nanoseconds, strongly enhancing photoluminescence and demonstrating an approach to stabilize them for photochemical applications. Full article
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10 pages, 1492 KiB  
Article
Evaluation of MAA Analogues as Potential Candidates to Increase Photostability in Sunscreen Formulations
by Jacobo Soilán, Leonardo López-Cóndor, Beatriz Peñín, José Aguilera, María Victoria de Gálvez, Diego Sampedro and Raúl Losantos
Photochem 2024, 4(1), 128-137; https://0-doi-org.brum.beds.ac.uk/10.3390/photochem4010007 - 6 Feb 2024
Viewed by 575
Abstract
Avobenzone is one of the most widely used sunscreens in skin care formulations, but suffers from some drawbacks, including photo instability. To mitigate this critical issue, the use of octocrylene as a stabilizer is a common approach in these products. However, octocrylene has [...] Read more.
Avobenzone is one of the most widely used sunscreens in skin care formulations, but suffers from some drawbacks, including photo instability. To mitigate this critical issue, the use of octocrylene as a stabilizer is a common approach in these products. However, octocrylene has been recently demonstrated to show potential phototoxicity. The aim of this work is to analyze the performance of a series of mycosporine-like amino acid (MAA)-inspired compounds to act as avobenzone stabilizers as an alternative to octocrylene. Different avobenzone/MAA analogue combinations included in galenic formulations were followed under increasing doses of solar-simulated UV radiation. Some of the synthetic MAA analogues analyzed were able to increase by up to two times the UV dose required for 50% of avobenzone photobleaching. We propose some of these MAA analogues as new candidates to act as avobenzone-stabilizing compounds in addition to their UV absorbance and antioxidant properties, together with a facile synthesis. Full article
(This article belongs to the Special Issue Feature Papers in Photochemistry II)
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17 pages, 5179 KiB  
Article
Physicochemical Properties of Tungsten Trioxide Photoanodes Fabricated by Wet Coating of Soluble, Particulate, and Mixed Precursors
by Valli Kamala Laxmi Ramya Chittoory, Marketa Filipsika, Radim Bartoš, Marcela Králová and Petr Dzik
Photochem 2024, 4(1), 111-127; https://0-doi-org.brum.beds.ac.uk/10.3390/photochem4010006 - 1 Feb 2024
Viewed by 759
Abstract
Advanced oxidation processes are emerging technologies for the decomposition of organic pollutants in various types of water by harnessing solar energy. The purpose of this study is to examine the physicochemical characteristics of tungsten(VI) oxide (WO3) photoanodes, with the aim of [...] Read more.
Advanced oxidation processes are emerging technologies for the decomposition of organic pollutants in various types of water by harnessing solar energy. The purpose of this study is to examine the physicochemical characteristics of tungsten(VI) oxide (WO3) photoanodes, with the aim of enhancing oxidation processes in the treatment of water. The fabrication of WO3 coatings on conductive fluorine-doped tin oxide (FTO) substrates was achieved through a wet coating process that utilized three different liquid formulations: a dispersion of finely milled WO3 particles, a fully soluble WO3 precursor (acetylated peroxo tungstic acid), and a combination of both (applying a brick-and-mortar strategy). Upon subjecting the WO3 coatings to firing at a temperature of 450 °C, it was observed that their properties exhibited marked variations. The fabricated photoanodes are examined using a range of analytical techniques, including profilometry, thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), and voltammetry. The experimental data suggest that the layers generated through the combination of particulate ink and soluble precursor (referred to as the brick-and-mortar building approach) display advantageous physicochemical properties, rendering them suitable for use as photoanodes in photoelectrochemical cells. Full article
(This article belongs to the Topic New Materials and Advanced Applications in Photocatalysis)
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54 pages, 2124 KiB  
Article
Inverse Problems in Pump–Probe Spectroscopy
by Denis S. Tikhonov, Diksha Garg and Melanie Schnell
Photochem 2024, 4(1), 57-110; https://0-doi-org.brum.beds.ac.uk/10.3390/photochem4010005 - 31 Jan 2024
Viewed by 946
Abstract
Ultrafast pump–probe spectroscopic studies allow for deep insights into the mechanisms and timescales of photophysical and photochemical processes. Extracting valuable information from these studies, such as reactive intermediates’ lifetimes and coherent oscillation frequencies, is an example of the inverse problems of chemical kinetics. [...] Read more.
Ultrafast pump–probe spectroscopic studies allow for deep insights into the mechanisms and timescales of photophysical and photochemical processes. Extracting valuable information from these studies, such as reactive intermediates’ lifetimes and coherent oscillation frequencies, is an example of the inverse problems of chemical kinetics. This article describes a consistent approach for solving this inverse problem that avoids the common obstacles of simple least-squares fitting that can lead to unreliable results. The presented approach is based on the regularized Markov Chain Monte-Carlo sampling for the strongly nonlinear parameters, allowing for a straightforward solution of the ill-posed nonlinear inverse problem. The software to implement the described fitting routine is introduced and the numerical examples of its application are given. We will also touch on critical experimental parameters, such as the temporal overlap of pulses and cross-correlation time and their connection to the minimal reachable time resolution. Full article
(This article belongs to the Special Issue Feature Papers in Photochemistry II)
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17 pages, 2920 KiB  
Article
The Rhodamine–Perylene Compact Electron Donor–Acceptor Dyad: Spin-Orbit Charge-Transfer Intersystem Crossing and the Energy Balance of the Triplet Excited States
by Muhammad Imran, Dongyi Liu, Kaiyue Ye, Xue Zhang and Jianzhang Zhao
Photochem 2024, 4(1), 40-56; https://0-doi-org.brum.beds.ac.uk/10.3390/photochem4010004 - 29 Jan 2024
Viewed by 851
Abstract
We prepared a rhodamine (RB)–perylene (Pery) compact electron donor/acceptor dyad (RB–Pery) to study the spin-orbit charge-transfer intersystem crossing (SOCT–ISC). The UV–vis absorption spectrum indicates a negligible electronic interaction between the donor and acceptor at ground state. However, the fluorescence of both [...] Read more.
We prepared a rhodamine (RB)–perylene (Pery) compact electron donor/acceptor dyad (RB–Pery) to study the spin-orbit charge-transfer intersystem crossing (SOCT–ISC). The UV–vis absorption spectrum indicates a negligible electronic interaction between the donor and acceptor at ground state. However, the fluorescence of both the RB and Pery units are quenched in the dyad, which is attributed to the photoinduced electron transfer, supported by the electrochemical studies. Nanosecond transient absorption (ns-TA) spectra show delocalized triplet states, i.e., there is an excited-state equilibrium between Pery and the RB triplet states. The triplet state lifetime was determined as 109.8 μs. With intermolecular triplet–triplet energy transfer, monitored using ns-TA spectra, the triplet-state energy balance between RB and Pery in RB–Pery was confirmed. The proposed cascade photophysical processes of the dyad are 1RB*-Pery→RB–Pery+•→[3RB*-Pery↔RB-3Pery*]. Moreover, long-lived rhodamine radical cation (in milliseconds) was detected in both deaerated/aerated non-polar or low-polarity solvents (i.e., p-xylene, toluene). The potential energy curve of the dyad against the variation in the dihedral angle between the two units indicates large torsional freedom (53°~128°) in RB–Pery, which leads to inefficient SOCT–ISC; consequently, low singlet-oxygen quantum yields (ΦΔ = 2~8%) were observed. Full article
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16 pages, 2649 KiB  
Article
Interactions of CdSe Nanocrystals with Cationic Proteins Extracted from Moringa oleifera Seeds
by Likius Shipwiisho Daniel, Salatiel Kapofi, Martha Kandawa-Schulz and Habauka Majority Kwaambwa
Photochem 2024, 4(1), 24-39; https://0-doi-org.brum.beds.ac.uk/10.3390/photochem4010003 - 15 Jan 2024
Viewed by 843
Abstract
Even with significant developments in nanoscience, relatively little is known about the interactions of nanocrystal semiconducting materials with bio-macromolecules. To investigate the interfacial phenomena of cadmium selenide quantum dot (CdSe QD) nanocrystals with proteins extracted from Moringa oleifera seeds, different concentrations of cadmium [...] Read more.
Even with significant developments in nanoscience, relatively little is known about the interactions of nanocrystal semiconducting materials with bio-macromolecules. To investigate the interfacial phenomena of cadmium selenide quantum dot (CdSe QD) nanocrystals with proteins extracted from Moringa oleifera seeds, different concentrations of cadmium selenide quantum dots–Moringa oleifera seed protein (CdSe–MSP) complexes were prepared. Respective CdSe QDs with hexagonal phase and crystalline size in the range of 4–7 nm were synthesized and labelled with the purified mesoporous MSP having a surface area of 8.4 m2/g. The interaction mechanism between CdSe QDs and MSP was studied using UV–Vis absorption, fluorescence emission and Fourier Transform Infrared spectroscopies. The UV–Vis absorption spectra showed absorption bands of CdSe–MSP complexes at 546.5 nm. The fluorescence intensity of CdSe QDs was found to decrease with increasing concentration of MSP. The thermodynamic potentials Hθ (−321.3 × 103 Jmol−1); Sθ (156.0 JK−1mol−1) and Gθ (−46.6 × 103 Jmol−1) were also calculated. The stability of the complex found is strongly influenced by electrostatics interaction and surface-bound complexation equilibrium attraction. This information can help to elucidate the surface characteristics of MSP and its potential interactions with other molecules or nanoparticles. Full article
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10 pages, 343 KiB  
Article
Survey of T1 and T2 Energies of Intramolecular Singlet Fission Chromophores
by Guoying Yao, Zhenyu Yang and Tao Zeng
Photochem 2024, 4(1), 14-23; https://0-doi-org.brum.beds.ac.uk/10.3390/photochem4010002 - 10 Jan 2024
Viewed by 825
Abstract
Singlet fission is a desired process in photovoltaics since it enhances photoelectric conversion efficiency. Intramolecular singlet fission is of special interest as the fission efficiency can be improved through tuning configurations between chromophore units that are covalently connected. However, intramolecular singlet fission chromophores [...] Read more.
Singlet fission is a desired process in photovoltaics since it enhances photoelectric conversion efficiency. Intramolecular singlet fission is of special interest as the fission efficiency can be improved through tuning configurations between chromophore units that are covalently connected. However, intramolecular singlet fission chromophores feature a large tetraradical character, and may tend to dissatisfy the ET2>2ET1 criterion for all singlet fission chromophores, intramolecular or not. We performed spin-flip time-dependent density functional theory calculations for a collection of representative intramolecular singlet fission chromophores to show that this is indeed the case. Full article
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13 pages, 2728 KiB  
Article
Twisted 8-Acyl-1-dialkyl-amino-naphthalenes Emit from a Planar Intramolecular Charge Transfer Excited State
by Christopher Abelt and Kirsten Sweigart
Photochem 2024, 4(1), 1-13; https://0-doi-org.brum.beds.ac.uk/10.3390/photochem4010001 - 4 Jan 2024
Viewed by 695
Abstract
Fluorescence from dialkylamino donor–acyl acceptor substituted 1,8-naphthalene derivatives can occur either from a planar (PICT) or a twisted (TICT) intramolecular charge transfer excited state. The photophysical properties of 8-acetyl-1-(dimethyl-amino)naphthalene (3) and 8-pivaloyl-1-(dimethyl-amino)naphthalene (4) are compared with 1-methyl-2,3-dihydronaphtho[1,8-bc]azepin-4(1H)-one (5 [...] Read more.
Fluorescence from dialkylamino donor–acyl acceptor substituted 1,8-naphthalene derivatives can occur either from a planar (PICT) or a twisted (TICT) intramolecular charge transfer excited state. The photophysical properties of 8-acetyl-1-(dimethyl-amino)naphthalene (3) and 8-pivaloyl-1-(dimethyl-amino)naphthalene (4) are compared with 1-methyl-2,3-dihydronaphtho[1,8-bc]azepin-4(1H)-one (5). In 3 and 4, both the carbonyl and amino groups are forced to twist out of the plane of the naphthalene ring. In 5, these groups are nearly coplanar with the naphthalene. Neither 3 nor 4 fluoresce as strongly as 5, but all three show similar degrees of solvato-chromism and all are strongly quenched by alcohol solvents. Nitrile 6, 8-cyano-1-(dimethyl-amino)naphthalene, does not show the same degree of solvato-chromism as 35, nor is it as affected by alcohols. Calculations corroborate the experimental results, indicating that 35 emit from a PICT excited state. Full article
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