Photochem

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19 pages, 12218 KiB

Open AccessArticle

Excited-State Dynamics of Carbazole and tert-Butyl-Carbazole in Thin Films

by Konstantin Moritz Knötig, Domenic Gust, Kawon Oum and Thomas Lenzer

Photochem 2024, 4(2), 179-197; https://doi.org/10.3390/photochem4020011 - 9 Apr 2024

Viewed by 1059

Thin films of carbazole (Cz) derivatives are frequently used in organic electronics, such as organic light-emitting diodes (OLEDs). Because of the proximity of the Cz units, the excited-state relaxation in such films is complicated, as intermolecular pathways, such as singlet–singlet annihilation (SSA), kinetically [...] Read more.

Thin films of carbazole (Cz) derivatives are frequently used in organic electronics, such as organic light-emitting diodes (OLEDs). Because of the proximity of the Cz units, the excited-state relaxation in such films is complicated, as intermolecular pathways, such as singlet–singlet annihilation (SSA), kinetically compete with the emission. Here, we provide an investigation of two benchmark systems employing neat carbazole and 3,6-di-tert-butylcarbazole (t-Bu-Cz) films and also their thin film blends with poly(methyl methacrylate) (PMMA). These are investigated by a combination of atomic force microscopy (AFM), femtosecond and nanosecond transient absorption spectroscopy (fs-TA and ns-TA) and time-resolved fluorescence. Excitonic J-aggregate-type features are observed in the steady-state absorption and emission spectra of the neat films. The S₁ state shows a broad excited-state absorption (ESA) spanning the entire UV–Vis–NIR range. At high S₁ exciton number densities of about 4 × 10¹⁸ cm⁻³, bimolecular diffusive S₁–S₁ annihilation is found to be the dominant SSA process in the neat films with a rate constant in the range of 1–2 × 10⁻⁸ cm³ s⁻¹. SSA produces highly vibrationally excited molecules in the electronic ground state (S₀*), which cool down slowly by heat transfer to the quartz substrate. The results provide relevant photophysical insight for a better microscopic understanding of carbazole relaxation in thin-film environments. Full article

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

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16 pages, 7427 KiB

Open AccessArticle

Excited-State Dynamics of Carbazole and tert-Butyl-Carbazole in Organic Solvents

by Konstantin Moritz Knötig, Domenic Gust, Thomas Lenzer and Kawon Oum

Photochem 2024, 4(2), 163-178; https://doi.org/10.3390/photochem4020010 - 30 Mar 2024

Cited by 1 | Viewed by 1337

Abstract

Carbazole-based molecular units are ubiquitous in organic optoelectronic materials; however, the excited-state relaxation of these compounds is still underexplored. Here, we provide a detailed investigation of carbazole (Cz) and 3,6-di-tert-butylcarbazole (t-Bu-Cz) in organic solvents using femtosecond and nanosecond UV–Vis–NIR [...] Read more.

Carbazole-based molecular units are ubiquitous in organic optoelectronic materials; however, the excited-state relaxation of these compounds is still underexplored. Here, we provide a detailed investigation of carbazole (Cz) and 3,6-di-tert-butylcarbazole (t-Bu-Cz) in organic solvents using femtosecond and nanosecond UV–Vis–NIR transient absorption spectroscopy, as well as time-resolved fluorescence experiments upon photoexcitation in the deep-UV range. The initially prepared S_x singlet state has a (sub-)picosecond lifetime and decays to the S₁ state by internal conversion (IC). The S₁ state exhibits absorption peaks at 350, 600 and 1100 nm and has a lifetime of 13–15 ns, which is weakly dependent on the solvent. Energy transfer from vibrationally hot S₁ molecules (S₁*) to the surrounding solvent molecules takes place with a time constant of 8–20 ps. The T₁ triplet state is populated by intersystem crossing (ISC) from S₁ with a typical quantum yield of 51–56% and shows a lifetime which is typically in the few microseconds regime. The S₁ and T₁ states of both carbazole compounds in solution are strongly quenched by O₂. Two-photon excitation leads to the formation of a small amount of the respective radical cation. The influence of the tert-butyl substituents on the photophysics is relatively weak and mainly reflects itself in a small increase in the Stokes shift. The results provide important photophysical information for the interpretation of carbazole relaxation in more complex environments. Full article

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

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10 pages, 1492 KiB

Open AccessArticle

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://doi.org/10.3390/photochem4010007 - 6 Feb 2024

Cited by 2 | Viewed by 958

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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54 pages, 2124 KiB

Open AccessArticle

Inverse Problems in Pump–Probe Spectroscopy

by Denis S. Tikhonov, Diksha Garg and Melanie Schnell

Photochem 2024, 4(1), 57-110; https://doi.org/10.3390/photochem4010005 - 31 Jan 2024

Cited by 2 | Viewed by 1410

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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12 pages, 2103 KiB

Open AccessArticle

E–Z Photoisomerization in Proton-Modulated Photoswitchable Merocyanine Based on Benzothiazolium and o-Hydroxynaphthalene Platform

by Aleksey A. Vasilev, Stanislav Baluschev, Sonia Ilieva and Diana Cheshmedzhieva

Photochem 2023, 3(2), 301-312; https://doi.org/10.3390/photochem3020018 - 19 Jun 2023

Viewed by 1743

Abstract

The potential of E–Z photoisomerization in molecular organic light-to-thermal conversion and storage in an E–styryl merocyanine system was studied in a polar acidic medium. A photoswitchable styryl merocyanine dye (E)-2-(2-(2-hydroxynaphthalen-1-yl)vinyl)-3,5-dimethylbenzo[d]thiazol-3-ium iodide was synthesized for the first [...] Read more.

The potential of E–Z photoisomerization in molecular organic light-to-thermal conversion and storage in an E–styryl merocyanine system was studied in a polar acidic medium. A photoswitchable styryl merocyanine dye (E)-2-(2-(2-hydroxynaphthalen-1-yl)vinyl)-3,5-dimethylbenzo[d]thiazol-3-ium iodide was synthesized for the first time. The reversible E–Z photoisomerisation of the dye was investigated using UV-Vis spectroscopy and DFT calculations. E–Z isomerization was induced through the use of visible light irradiation (λ = 450 nm). The obtained experimental and theoretical results confirm the applicability of the Z and E isomers for proton-triggered light harvesting. Full article

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

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13 pages, 1692 KiB

Open AccessArticle

Effect of Benzophenone Type UV Filters on Photodegradation of Co-existing Sulfamethoxazole in Water

by Dilini Kodikara, Zhongyu Guo and Chihiro Yoshimura

Photochem 2023, 3(2), 288-300; https://doi.org/10.3390/photochem3020017 - 1 Jun 2023

Cited by 1 | Viewed by 2102

Abstract

Benzophenones (BPs) frequently occur in water environments, and they are able to both screen UV light and to sensitize reactive intermediate (RI) production. However, BPs have largely been overlooked as a background water component when studying photodegradation of co-existing organic micropollutants (OMPs). Therefore, [...] Read more.

Benzophenones (BPs) frequently occur in water environments, and they are able to both screen UV light and to sensitize reactive intermediate (RI) production. However, BPs have largely been overlooked as a background water component when studying photodegradation of co-existing organic micropollutants (OMPs). Therefore, in this study, we investigated the influence of BP and its derivative oxybenzone (BP3) on the degradation of the co-existing model OMP sulfamethoxazole (SMX). A series of photodegradation experiments were conducted covering a range of BPs concentrations in μg/L levels, and the degradation of 1.00 μM of SMX was studied. The addition of BP at 0.10 μM, 0.25 μM, and 0.30 μM, and BP3 at 0.10 μM and 0.25 μM, significantly increased the first order degradation rate constant of 1.00 μM of SMX (k_obs(BP)) by 36.2%, 50.0%, 7.3%, 31.5%, and 36.2% respectively, compared to that in the absence of any BPs. The maximum indirect photodegradation induced by BP and BP3 reached 33.8% and 27.7%, respectively, as a percentage of the observed SMX degradation rate at the [BPs]/[SMX] ratio of 0.25. In general, triplet excited dissolved organic matter (³SMX*, ³BP*, and ³BP3*) played the major role in the photosensitizing ability of BPs. The results further implied that the increase of SMX degradation at the molar ratio of 0.25 was possibly due to ³BP* for the mixture of SMX and BP. Overall, this study revealed the sensitizing ability of BP and BP3 on the co-existing OMP, SMX, in water for the first time. Our findings can be applied to other BP type UV filters which are similar to BP and PB3 in molecular structure. Full article

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

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14 pages, 6942 KiB

Open AccessArticle

Synthesis and Characterization of New Tetradentate N₂O₂-Based Schiff’s Base Cu (II) Complexes for Dye Photodegradation

by Rohini Vallavoju, Ranjith Kore, Radhika Parikirala, Mahesh Subburu, Ramesh Gade, Vipin Kumar, Matta Raghavender, Prabhakar Chetti and Someshwar Pola

Photochem 2023, 3(2), 274-287; https://doi.org/10.3390/photochem3020016 - 11 May 2023

Cited by 3 | Viewed by 2435

Abstract

We have reported tetradentate ligands (salophen) coordinated with N and O atoms that led to the Cu (II) complexes. These Cu (II) complexes (C-1 and C-2) were firstly established by using elemental analysis and confirmed by mass spectra. At the same time, the [...] Read more.

We have reported tetradentate ligands (salophen) coordinated with N and O atoms that led to the Cu (II) complexes. These Cu (II) complexes (C-1 and C-2) were firstly established by using elemental analysis and confirmed by mass spectra. At the same time, the characterization of C-1 and C-2 complexes is performed by using several spectroscopic methods and morphological analysis. The bandgap values of the C-1 and C-2 complexes are evaluated with UV-vis DRS spectra. The PL spectral data and photocurrent curves clearly indicated the small recombination rate of the hole–electron pair. The synthesized C-1 and C-2 complexes’ photocatalytic properties were examined for the degradation of cationic dyes such as methylene blue (MB λ_max.= 654 nm) and methyl violet (MV λ_max.= 590 nm) below visible-light action. The C-2 complex is more active than the C-1 complex because of its high photostability, small band-gap energy, and low recombination rate for hole–electron pair separation, and improved visible-light character, which encourages the generation of hydroxyl radical species throughout the photodegradation process. Scavenger probes were used to identify the dynamic species for the photodegradation of dyes, and a mechanism investigation was established. Full article

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

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11 pages, 1409 KiB

Open AccessArticle

Photoprotective Effects of Selected Polyphenols and Antioxidants on Naproxen Photodegradability in the Solid-State

by Kohei Kawabata, Ayano Miyoshi and Hiroyuki Nishi

Photochem 2022, 2(4), 880-890; https://doi.org/10.3390/photochem2040056 - 6 Nov 2022

Cited by 6 | Viewed by 1854

Abstract

Photostabilization is an important methodology to ensure both the quality and quantity of photodegradable pharmaceuticals. The purpose of our study is to develop a photostabilization strategy focused on the addition of photostabilizers. In this study, the protective effects of selected polyphenols and antioxidants [...] Read more.

Photostabilization is an important methodology to ensure both the quality and quantity of photodegradable pharmaceuticals. The purpose of our study is to develop a photostabilization strategy focused on the addition of photostabilizers. In this study, the protective effects of selected polyphenols and antioxidants on naproxen (NPX) photodegradation in the solid state were evaluated. Residual amounts of NPX were determined by high-performance liquid chromatography (HPLC), and the protective effects of tested additives on NPX photodegradation induced by ultraviolet light (UV) irradiation were evaluated. As a result, quercetin, curcumin, and resveratrol suppressed NPX photodegradation completely. When they were mixed with NPX, the residual amounts of NPX after UV irradiation were significantly higher compared to that without additives, and comparable to those of their control samples. In addition, to clarify the mechanisms of the highly protective effects of these additives on NPX photodegradation, their antioxidative potencies, and UV filtering potencies were determined. There was no correlation between photoprotective effects and antioxidative potencies among selected polyphenols and antioxidants although photoprotective additives showed more significant UV absorption compared to NPX. From these results, it is clarified that a higher UV filtering activity is necessary for a better photostabilizer to photodegradable pharmaceuticals in the solid state. Full article

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

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