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14 pages, 1636 KiB

Open AccessArticle

Characterization of Excited-State Electronic Structure in Diblock π-Conjugated Oligomers with Adjustable Linker Electronic Coupling

by Habtom B. Gobeze, Muhammed Younus, Michael D. Turlington, Sohel Ahmed and Kirk S. Schanze

Molecules 2024, 29(11), 2678; https://doi.org/10.3390/molecules29112678 - 5 Jun 2024

Viewed by 1324

Abstract

Diblock conjugated oligomers are π-conjugated molecules that contain two segments having distinct frontier orbital energies and HOMO-LUMO gap offsets. These oligomers are of fundamental interest to understand how the distinct π-conjugated segments interact and modify their excited state properties. The current paper reports [...] Read more.

Diblock conjugated oligomers are π-conjugated molecules that contain two segments having distinct frontier orbital energies and HOMO-LUMO gap offsets. These oligomers are of fundamental interest to understand how the distinct π-conjugated segments interact and modify their excited state properties. The current paper reports a study of two series of diblock oligomers that contain oligothiophene (T_n) and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT) segments that are coupled by either ethynyl (-C≡C-) or trans-(-C≡C-)₂Pt(II)(PBu₃)₂ acetylide linkers. In these structures, the T_n segment is electron rich (donor), and the TBT is electron poor (acceptor). The diblock oligomers are characterized by steady-state and time-resolved spectroscopy, including UV-visible absorption, fluorescence, fluorescence lifetimes, and ultrafast transient absorption spectroscopy. Studies are compared in several solvents of different polarity and with different excitation wavelengths. The results reveal that the (-C≡C-) linked oligomers feature a delocalized excited state that takes on a charge transfer (CT) character in more polar media. In the (-C≡C-)₂Pt(II)(PBu₃)₂-linked oligomers, there is weak coupling between the T_n and TBT segments. Consequently, short wavelength excitation selectively excites the T_n segment, which then undergoes ultrafast energy transfer (~1 ps) to afford a TBT-localized excited state. Full article

(This article belongs to the Special Issue Current Advances in Photochemistry)

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14 pages, 5429 KiB

Open AccessArticle

Pollutant Photodegradation Affected by Evaporative Water Concentration in a Climate Change Scenario

by Arianna Rosso and Davide Vione

Molecules 2024, 29(11), 2655; https://doi.org/10.3390/molecules29112655 - 4 Jun 2024

Viewed by 636

Abstract

Evaporative water concentration takes place in arid or semi-arid environments when stationary water bodies, such as lakes or ponds, prevalently lose water by evaporation, which prevails over outflow or seepage into aquifers. Absence or near-absence of precipitation and elevated temperatures are important prerequisites [...] Read more.

Evaporative water concentration takes place in arid or semi-arid environments when stationary water bodies, such as lakes or ponds, prevalently lose water by evaporation, which prevails over outflow or seepage into aquifers. Absence or near-absence of precipitation and elevated temperatures are important prerequisites for the process, which has the potential to deeply affect the photochemical attenuation of pollutants, including contaminants of emerging concern (CECs). Here we show that water evaporation would enhance the phototransformation of many CECs, especially those undergoing degradation mainly through direct photolysis and triplet-sensitized reactions. In contrast, processes induced by hydroxyl and carbonate radicals would be inhibited. Our model results suggest that the photochemical impact of water evaporation might increase in the future in several regions of the world, with no continent likely being unaffected, due to the effects of local precipitation decrease combined with an increase in temperature that facilitates evaporation. Full article

(This article belongs to the Special Issue Current Advances in Photochemistry)

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14 pages, 4493 KiB

Open AccessArticle

Visible Light-Promoted Oxidative Cross-Coupling of Alcohols to Esters

by Andrea Dellisanti, Elisa Chessa, Andrea Porcheddu, Massimo Carraro, Luisa Pisano, Lidia De Luca and Silvia Gaspa

Molecules 2024, 29(3), 570; https://doi.org/10.3390/molecules29030570 - 23 Jan 2024

Viewed by 2077

Abstract

Ester is one of the most significant functional groups in organic chemistry and is enclosed in several valued molecules. Usually, esters are prepared through the acid-catalyzed esterification reaction of carboxylic acids with alcohols, transesterification of esters with alcohols, or via activation of carboxylic [...] Read more.

Ester is one of the most significant functional groups in organic chemistry and is enclosed in several valued molecules. Usually, esters are prepared through the acid-catalyzed esterification reaction of carboxylic acids with alcohols, transesterification of esters with alcohols, or via activation of carboxylic acids followed by the addition of alcohols. However, these procedures typically imply the excess use of reactants and harsh reaction conditions. Visible light-mediated photoreactions have been disclosed to display a safe, sustainable, and accessible alternative to traditional methods, and to lead new reactivity modes in organic procedures. In this context, we propose a transition metal-based and organic-based photocatalyst-free synthesis of esters from alcohols induced by visible light. The methodology can be carried out using sunlight or artificial visible light as a solar simulator or a blue LED source. Full article

(This article belongs to the Special Issue Current Advances in Photochemistry)

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14 pages, 2295 KiB

Open AccessArticle

Possible Effects of Changes in Carbonate Concentration and River Flow Rate on Photochemical Reactions in Temperate Aquatic Environments

by Davide Vione, Federica Saglia and Carola Pelazza

Molecules 2023, 28(20), 7072; https://doi.org/10.3390/molecules28207072 - 13 Oct 2023

Cited by 2 | Viewed by 1045

Abstract

In temperate environments, climate change could affect water pH by inducing enhanced dissolution of CaSO₄ followed by biological sulphate reduction, with the potential to basify water due to H⁺ consumption. At the same time, increased atmospheric CO₂ could enhance weathering [...] Read more.

In temperate environments, climate change could affect water pH by inducing enhanced dissolution of CaSO₄ followed by biological sulphate reduction, with the potential to basify water due to H⁺ consumption. At the same time, increased atmospheric CO₂ could enhance weathering of carbonate rocks (e.g., dolomite) and increase the total concentration of dissolved carbonate species. Both processes enhance phototransformation by the carbonate radical (CO₃^•−), as shown for the non-steroidal anti-inflammatory drug paracetamol, provided that the dissolved organic carbon of water does not undergo important fluctuations. Climate change could also affect hydrology, and prolonged drought periods might considerably decrease flow rates in rivers. This is a substantial problem because wastewater pollutants become less diluted and, as a result, can exert more harmful effects due to increased concentrations. At the same time, in low-flow conditions, water is also shallower and its flow velocity is decreased. Photochemical reactions become faster because shallow water is efficiently illuminated by sunlight, and they also have more time to occur because water takes longer to cover the same river stretch. As a result, photodegradation of contaminants is enhanced, which offsets lower dilution but only at a sufficient distance from the wastewater outlet; this is because photoreactions need time (which translates into space for a flowing river) to attenuate pollution. Full article

(This article belongs to the Special Issue Current Advances in Photochemistry)

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18 pages, 4098 KiB

Open AccessArticle

Excited-State Dynamics Leading Either to Triplet Formation or Coordinative Expansion following Photolysis of Cu(II)-Porphyrins: A DFT, TD-DFT, Luminescence and Femtosecond Time-Resolved Absorbance Study

by Ross J. McGarry, Lazaros Varvarezos, Mary T. Pryce and Conor Long

Molecules 2023, 28(17), 6310; https://doi.org/10.3390/molecules28176310 - 29 Aug 2023

Viewed by 1561

Abstract

The photophysical properties of Cu(II) complexes with 5,10,15,20-meso-tetrakis(phenyl)porphyrin and 5,10,15,20-meso-tetrakis(N-methylpyridium-4-yl)porphyrin are examined via the luminescence and femtosecond time-resolved absorbance methods, respectively. These studies are supported by DFT and TD-DFT calculations, which highlight the [...] Read more.

The photophysical properties of Cu(II) complexes with 5,10,15,20-meso-tetrakis(phenyl)porphyrin and 5,10,15,20-meso-tetrakis(N-methylpyridium-4-yl)porphyrin are examined via the luminescence and femtosecond time-resolved absorbance methods, respectively. These studies are supported by DFT and TD-DFT calculations, which highlight the important role played by ligand-to-metal charge-transfer states in directing the system toward either intersystem crossing to the triplet hypersurface or coordinative expansion to a five-coordinate quasi-stable intermediate. The latter processes occur when the porphyrin is photolyzed in the presence of suitably located Lewis bases. Femtosecond time-resolved absorbance measurements of Cu(II)-5,10,15,20-meso-tetrakis(N-methylpyridium-4-yl)porphyrin confirm that the coordinative expansion in water occurs in approximately 700 fs, while crossing to the triplet hypersurface takes approximately 140 fs in the same solvent. These processes are mutually exclusive, although both can occur simultaneously depending on the environment of the porphyrin. The ratio of the two processes depends on the relative orientation of the Lewis base with respect to the copper atom at the time of excitation. As a consequence, copper porphyrins such as these are excellent probes in the environment of the porphyrin and can be used to identify the location of the porphyrin when interacting with DNA fragments. Full article

(This article belongs to the Special Issue Current Advances in Photochemistry)

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16 pages, 5261 KiB

Open AccessArticle

Effect of the Synthetic Parameters over ZnO in the CO₂ Photoreduction

by Danny Zanardo, Giulia Forghieri, Elena Ghedini, Federica Menegazzo, Alessia Giordana, Giuseppina Cerrato, Elti Cattaruzza, Alessandro Di Michele, Giuseppe Cruciani and Michela Signoretto

Molecules 2023, 28(12), 4798; https://doi.org/10.3390/molecules28124798 - 16 Jun 2023

Cited by 2 | Viewed by 1317

Abstract

Zinc oxide (ZnO) is an attractive semiconductor material for photocatalytic applications, owing to its opto-electronic properties. Its performances are, however, strongly affected by the surface and opto-electronic properties (i.e., surface composition, facets and defects), in turn related to the synthesis conditions. The knowledge [...] Read more.

Zinc oxide (ZnO) is an attractive semiconductor material for photocatalytic applications, owing to its opto-electronic properties. Its performances are, however, strongly affected by the surface and opto-electronic properties (i.e., surface composition, facets and defects), in turn related to the synthesis conditions. The knowledge on how these properties can be tuned and how they are reflected on the photocatalytic performances (activity and stability) is thus essential to achieve an active and stable material. In this work, we studied how the annealing temperature (400 °C vs. 600 °C) and the addition of a promoter (titanium dioxide, TiO₂) can affect the physico-chemical properties of ZnO materials, in particular surface and opto-electronic ones, prepared through a wet-chemistry method. Then, we explored the application of ZnO as a photocatalyst in CO₂ photoreduction, an appealing light-to-fuel conversion process, with the aim to understand how the above-mentioned properties can affect the photocatalytic activity and selectivity. We eventually assessed the capability of ZnO to act as both photocatalyst and CO₂ adsorber, thus allowing the exploitation of diluted CO₂ sources as a carbon source. Full article

(This article belongs to the Special Issue Current Advances in Photochemistry)

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11 pages, 1805 KiB

Open AccessArticle

Photochemical Implications of Changes in the Spectral Properties of Chromophoric Dissolved Organic Matter: A Model Assessment for Surface Waters

by Nicole Altare and Davide Vione

Molecules 2023, 28(6), 2664; https://doi.org/10.3390/molecules28062664 - 15 Mar 2023

Cited by 2 | Viewed by 1424

Abstract

Chromophoric dissolved organic matter (CDOM) is the main sunlight absorber in surface waters and a very important photosensitiser towards the generation of photochemically produced reactive intermediates (PPRIs), which take part in pollutant degradation. The absorption spectrum of CDOM (A_CDOM(λ), unitless) [...] Read more.

Chromophoric dissolved organic matter (CDOM) is the main sunlight absorber in surface waters and a very important photosensitiser towards the generation of photochemically produced reactive intermediates (PPRIs), which take part in pollutant degradation. The absorption spectrum of CDOM (A_CDOM(λ), unitless) can be described by an exponential function that decays with increasing wavelength: A_CDOM(λ) = 100 d DOC A_o e⁻ ^S^λ, where d [m] is water depth, DOC [mg_C L⁻¹] is dissolved organic carbon, A_o [L mg_C⁻¹ cm⁻¹] is a pre-exponential factor, and S [nm⁻¹] is the spectral slope. Sunlight absorption by CDOM is higher when A_o and DOC are higher and S is lower, and vice versa. By the use of models, here we investigate the impact of changes in CDOM spectral parameters (A_o and S) on the steady-state concentrations of three PPRIs: the hydroxyl radical (^•OH), the carbonate radical (CO₃^•−), and CDOM excited triplet states (³CDOM*). A first finding is that variations in both A_o and S have impacts comparable to DOC variations on the photochemistry of CDOM, when reasonable parameter values are considered. Therefore, natural variability of the spectral parameters or their modifications cannot be neglected. In the natural environment, spectral parameters could, for instance, change because of photobleaching (prolonged exposure of CDOM to sunlight, which decreases A_o and increases S) or of the complex and still poorly predictable effects of climate change. A second finding is that, while the steady-state [³CDOM*] would increase with increasing A_CDOM (increasing A_o, decreasing S), the effect of spectral parameters on [^•OH] and [CO₃^•−] depends on the relative roles of CDOM vs. NO₃⁻ and NO₂⁻ as photochemical ^•OH sources. Full article

(This article belongs to the Special Issue Current Advances in Photochemistry)

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Review

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55 pages, 7312 KiB

Open AccessReview

Recent Advances in Light-Driven Semiconductor-Based Micro/Nanomotors: Optimization Strategies and Emerging Applications

by Vanessa R. A. Ferreira and Manuel A. Azenha

Molecules 2024, 29(5), 1154; https://doi.org/10.3390/molecules29051154 - 5 Mar 2024

Cited by 1 | Viewed by 2120

Abstract

Micro/nanomotors represent a burgeoning field of research featuring small devices capable of autonomous movement in liquid environments through catalytic reactions and/or external stimuli. This review delves into recent advancements in light-driven semiconductor-based micro/nanomotors (LDSM), focusing on optimized syntheses, enhanced motion mechanisms, and emerging [...] Read more.

Micro/nanomotors represent a burgeoning field of research featuring small devices capable of autonomous movement in liquid environments through catalytic reactions and/or external stimuli. This review delves into recent advancements in light-driven semiconductor-based micro/nanomotors (LDSM), focusing on optimized syntheses, enhanced motion mechanisms, and emerging applications in the environmental and biomedical domains. The survey commences with a theoretical introduction to micromotors and their propulsion mechanisms, followed by an exploration of commonly studied LDSM, emphasizing their advantages. Critical properties affecting propulsion, such as surface features, morphology, and size, are presented alongside discussions on external conditions related to light sources and intensity, which are crucial for optimizing the propulsion speed. Each property is accompanied by a theoretical background and conclusions drawn up to 2018. The review further investigates recent adaptations of LDSM, uncovering underlying mechanisms and associated benefits. A brief discussion is included on potential synergistic effects between different external conditions, aiming to enhance efficiency—a relatively underexplored topic. In conclusion, the review outlines emerging applications in biomedicine and environmental monitoring/remediation resulting from recent LDSM research, highlighting the growing significance of this field. The comprehensive exploration of LDSM advancements provides valuable insights for researchers and practitioners seeking to leverage these innovative micro/nanomotors in diverse applications. Full article

(This article belongs to the Special Issue Current Advances in Photochemistry)

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