Photochem

In this work, the photocatalytic reduction of CO₂ was innovatively tested with the simultaneous removal and mineralization of a textile contaminant, methylene blue (MB), which acts as a sacrificial agent. The process was carried out in a flow regime under atmospheric conditions, using a liquid-phase photoreactor under UVA illumination with a duration of 24 h per test. Two commercial TiO₂-based photocatalysts, P25 and P90 from Evonik, were used and surface modified through the photodeposition of metallic nanoparticles of Pt, Au, and Pd, as they did not show gas-phase products from CO₂ reduction on their own. The optimal pH was 5, the decreasing order of activity by metal was Pt > Au > Pd, and the optimal MB concentration was 20 ppm. The major products were CH₄ and H₂ in the gas phase. The presence of CH₄ was only detected in the presence of a CO₂ flow. In the liquid phase, carboxylic acids were also detected in small amounts, and in the test, 100 ppm of MB ethanol was additionally detected. A 100% degradation of MB and 72.5% mineralization was achieved under the conditions of highest CH₄ production (20 ppm MB at pH 5 with 4 g·L⁻¹ P25-0.70%Pt). Full article

Raman spectroscopy is a widely used technology in the biomedical field, including specific applications from cancer diagnosis to an active role in the pharmaceutical industry. Despite the extensive use of Raman spectroscopy in research studies, there are still some limitations to its applicability in daily clinical diagnosis. This review initially presents the main principles of Raman spectroscopy and then its most relevant applications in the biomedical field, exploring the main advantages, challenges, and limitations. Additionally, other Raman-based techniques are identified as alternatives to the conventional technique. Overall, this review aims to present the currently available applications of Raman spectroscopy in the biomedical field and future appropriate perspectives, as possible guidance for new Raman-based biomedical devices. Full article

In the light reactions of photosynthesis, reactive oxygen species (ROS), such as superoxide anion radical (O₂^•−), hydrogen peroxide (H₂O₂), singlet oxygen (¹O₂*), and hydroxyl radical (OH^•), are continuously generated at basal levels and are kept in homeostasis by the antioxidative enzymatic and non-enzymatic systems. Nevertheless, under abiotic or biotic stress conditions, this balance between the creation and elimination of ROS is disrupted, and the increased ROS production leads to oxidative stress, which is involved in the growth retardation of plants. However, ROS are also beneficial, since they trigger the plant’s defense mechanisms for handling oxidative stress and are fundamental signaling molecules for the regulation of a range of physiological functions under optimum growth conditions or environmental stress circumstances, activating a plethora of acclimation responses. Gaining insight into the relationship between ROS generation, ROS scavenging, and the protective role of ROS will contribute to improving agricultural sustainability in the face of global climate change. Full article

Four 8-acyl-1-pyrrolidinylnaphalenes are prepared where the acyl group is pivaloyl (6), benzoyl (7), benzyloxycarbonyl (8), and ethyloxycarbonyl (9). Crystal structures for 6–8 show that both the carbonyl and pyrrolidinyl groups are nearly perpendicular to the naphthalene ring. Esters 8 and 9 fluoresce more strongly than ketones 6 and 7. All show some solvatofluoro-chromic emission from a charge-transfer excited state. Calculations suggest that both the acyl and amino groups twist back toward planarity with the naphthalene in the relaxed first singlet excited state. With 8 and 9, co-planarity is within 20°, while with 6 and 7, the carbonyl approaches no closer than 30°. With 6 and 7, the charge-transfer emission is replaced with a shorter wavelength band with more polar solvents. Despite the twisted geometries and steric interference toward planarization, these systems do not show emission from a twisted intramolecular charge-transfer (TICT) state. Full article

Organic peroxy (ROO•) and hydroperoxy (•QOOH) radicals are key reactive intermediates that are formed via the oxidation of volatile organic compounds during combustion or in the Earth’s atmosphere. Their primary fate is continued unimolecular decay or bimolecular chemistry, the relative branching for which is heavily structure- and temperature-dependent. This article outlines a combined single- and multi-reference quantum chemical study to characterize the near-UV accessible electronically excited states of the prototypical ROO• and •QOOH intermediates, tert-butyl peroxy and hydroperoxy-tert-butyl radicals—the ground-state chemistries of which have been well studied both experimentally and computationally. Additionally, we simulate the electronic absorption profiles of these ROO• and •QOOH intermediates with a variety of multi- and single-reference methods. The results show an interesting conformer dependence on the electronically excited-state character and electronic absorption maxima of •QOOH. The results show promise for electronic absorption spectroscopy to be used as a selected probe for determining •QOOH conformers. Additionally, electronic absorption may contribute to the daytime removal of long-lived •QOOH intermediates formed in the troposphere. We expect that our studies will motivate experiments on the electronic absorption spectra of experimentally achievable ROO• and •QOOH. Full article

In this study, we investigated environmentally responsive photoluminescence color changes in water using an amphiphilic flavin derivative (1a) functionalized with an alkylsulfonate group. At low concentrations and room temperature, 1a exhibited a green emission. Upon increasing the concentration, thermodynamically stable micelle-like aggregates were formed, leading to a yellow emission. In contrast, under rapid freezing conditions, fibrous aggregates were formed under kinetic control, which also exhibited a yellow emission. These distinct aggregation modes are attributed to the cooperative effects of molecular design: the π-stacking ability of the tricyclic isoalloxazine core, flexible long alkyl chains, and the hydrophilic sulfonate moiety. This work demonstrates photoluminescent color switching based on aggregation-state control of a biogenic and potentially sustainable flavin luminophore, offering a new perspective for designing responsive and sustainable photofunctional materials. Full article

We determine the efficiency of generating singlet oxygen molecules through Raman excitation in distilled water. Focused nanosecond light pulses in the spectral blue region induce a Raman transition toward the singlet oxygen state, generating a Stokes signal in the red spectral region. The signal is proportional to the number of photons corresponding to the number of excited oxygen molecules. We calculate the efficiency by dividing the number of generated singlet oxygen molecules by the number of incoming pump photons, determining an efficiency of (8 ± 2) × 10⁻⁵ for water when pumping at 410 nm with a pulse energy of 13 mJ. We demonstrate that the Raman method results in no photobleaching, a phenomenon typically observed when photosensitizers are used. Thanks to this property, Raman excitation can continue for as long as the sample is irradiated, generating more singlet oxygen molecules over time than the photosensitization method. Full article

Aggregation-induced emission (AIE) luminogens are materials that exhibit enhanced light emission in the aggregated state, primarily due to the restriction of intramolecular motions, which reduces energy loss through non-radiative pathways. Tetraphenylethylene (TPE) and its derivatives are prominent examples of AIE-active materials, owing to their ease of synthesis, tuneable photophysical properties, and strong aggregation tendencies. This review provides an overview of the fundamental AIE mechanisms in TPE-based systems, with a focus on the role of restricted intramolecular rotation (RIR) and π-twisting in governing their emission behaviour. It explores the influence of molecular structure, electronic configuration, and intermolecular interactions on fluorescence properties. Furthermore, recent advances in practical applications of TPE-based AIE luminogens are highlighted across a spectrum of biological imaging domains, including cellular imaging, tissue and in vivo imaging, and organelle-targeted imaging. Additionally, their integration into multifunctional and theranostic platforms, along with the development of stimuli-responsive and self-assembled systems, underscores their versatility and expanding potential in biomedical research and diagnostics. This review aims to offer valuable insights into the design principles and functional potential of TPE-based AIE luminogens, guiding the development of next-generation materials for advanced bioimaging technologies. Full article

Accurate detection of water in organic solvents is essential for various industrial and analytical applications. In this study, we present a simple, rapid, and sensitive fluorescence-based method for water quantification using 1,5-diaminonaphthalene (1,5-DAN) as a solvatochromic probe. This method exploits the excited-state intramolecular charge transfer (ICT) behavior of 1,5-DAN, which undergoes a symmetry-breaking transition in the presence of protic solvents such as water, leading to a distinct redshift in its emission spectrum and a change from a structured double-band to a single ICT band. We demonstrate that, in solvents like acetonitrile and tetrahydrofuran, the emission maxima of 1,5-DAN correlate linearly with water content up to 100%, while ratiometric analysis of peak intensities allows for sensitive detection in low concentration ranges. This method achieved limits of detection as low as 0.08% (v/v) in MeCN, with high reproducibility and minimal sample preparation. Application to a real MeCN–water azeotrope confirms the method’s accuracy, matching classical refractometric measurements. Our findings highlight the potential of 1,5-DAN as a low-cost, efficient, and non-destructive fluorescent sensor for monitoring moisture in organic solvents, offering a practical alternative to conventional methods such as Karl Fischer titration for both bulk and trace water analysis. Full article

This study details how 3-(naphthalen-2-yl)-1-phenylprop-2-en-1-one (3NPEO) behaves in terms of photophysics when exposed to different solvents. The solvatochromic effect study reveals significant polarity shifts in the excited states of the 3NPEO compound, likely due to an intramolecular proton transfer mechanism. Measurements of dipole moments provide insight into their resonance structures in both ground and excited states. Electrochemical analysis revealed a reversible redox process, indicating a favorable charge transport potential. HOMO and LUMO energies of the compound were computed via oxidation and reduction potential standards. 3NPEO exhibits optimal one-photon and two-photon absorption characteristics, validating its suitability for visible wavelength laser applications in photonic devices. Furthermore, molecular docking and dynamics simulations demonstrated strong interactions between 3NPEO and the progesterone receptor enzyme, supported by structure–activity relationship (SAR) analyses. In vitro cytotoxicity assays on the MDAMB-231 breast cancer cell line showed moderate tumor cell inhibitory activity. Apoptosis studies confirmed the induction of both early and late apoptosis. These findings suggest that 3NPEO holds promise as a potential anticancer agent targeting the progesterone receptor in breast cancer cells. Overall, the findings highlight the substantial influence of solvent polarity on the photophysical properties and the design of more effective and stable therapeutic agents. Full article

Photosynthesis in plants and the electron transport chain in mitochondria are examples of life-sustaining electron transfer processes. The benzoquinones plastoquinone and ubiquinone are key components of these pathways that cycle through their oxidized and reduced forms. Previously, we reported direct photoreduction of biologically relevant quinones mediated by photosensitizers, red light and electron donors. Herein we examined direct photoreduction of the quinone imine 2,6-dichlorophenolindophenol (DCPIP) using red light, methylene blue as the photosensitizer and ethylenediaminetetraacetic acid (EDTA) as the electron donor. Photoreduction of DCPIP by methylene blue and EDTA was very pH-dependent, with three-fold enhanced rates at pH 6.9 vs. pH 7.4. Photochemical redox cycling of DCPIP produced hydrogen peroxide via singlet oxygen-dependent reoxidation of reduced DCPIP. Histidine enhanced photoreduction by scavenging singlet oxygen, whereas increased molecular oxygen exposure slowed DCPIP photoreduction. Attempts to photoreduce DCPIP with pheophorbide A, a chlorophyll metabolite, and triethanolamine as the electron donor in 20% dimethylformamide were unsuccessful. Photoreduced benzoquinones including 2,3-dimethoxy-5-methyl-p-benzoquinone (CoQ₀), methoxy-benzoquinone and methyl-benzoquinone were used to examine electron transfer to DCPIP. For photoreduced CoQ₀ and methoxy-benzoquinone, electron transfer to DCPIP was rapid and complete, whereas for reduced methyl benzoquinone, it was incomplete due to differences in reduction potential. Nonetheless, electron transfer from photoreduced quinols to DCPIP is a rapid and sensitive method to investigate quinone photoreduction by chlorophyll metabolites. Full article

Cyanotypes, known as photographs and architectural plans made by photo-reproduction from the 19th and 20th centuries, are subjects for conservation. Wet cleaning for conservation treatment has been reported to be unsuitable for cyanotypes because Prussian blue on cyanotypes is thought to move physically with the application of water. The manner in which Prussian blue is fixed onto the paper substrate is important for determining the treatment method. This study is the first step toward clarifying this mechanism. The presence of Prussian blue in cyanotypes was first confirmed using X-ray diffraction analysis (XRD). Then, the location of Prussian blue in the fibre was confirmed using optical microscopy and micro-Raman spectroscopy analysis, by observing the blue colour and by detecting its cyanide bond. With field-emission scanning electron microscopy (FE-SEM), particles approximately 20–100 nm in size were observed on the surface of cyanotype paper fibres, and particles approximately 20–50 nm in size were observed from the cross-section of the paper fibres. The location where the particles were observed agreed with the location where the blue colour was observed and cyanide bond was detected. The fact that the sensitiser solution soaked into the paper fibres and formed Prussian blue within the paper fibres when exposed to light is thought to be important for the blue fixation of cyanotypes. Full article

Quinolones and fluoroquinolones are heterocyclic compounds with important antibacterial properties, and they have been extensively used in medicinal chemistry to treat diverse bacterial infections. However, their clinical applications have been limited by several factors. On one side, there is an increasing number of resistant bacterial strains. On the other side, some of these heterocyclic compounds have shown several adverse effects such as photocarcinogenic cutaneous reactions, with the development of skin tumors. These adverse properties have motivated a large number of studies on the photophysical, photochemical and phototoxic properties of these compounds. In this review, several important chemical aspects about quinolones and fluoroquinolones are discussed. In the first sections, their basic structure is presented, along with some important physicochemical properties. In the next sections, their photochemical and photophysical processes are discussed. Upon photolysis in aqueous neutral conditions, these heterocyclic compounds generate several highly reactive intermediates that could initiate diverse reactions with molecules. In a biological environment, quinolones and fluoroquinolones are known to associate with biomolecules and generate complexes. Within these complexes, photophysical and photochemical processes generate intermediates, accelerating diverse reactions between biomolecules and these heterocyclic compounds. For several decades, diverse fluoroquinolones have been prepared for the treatment of a variety of bacterial infections. However, their prescription has been restricted due to the associated severe side effects. In the last decade, new derivatives have been developed and are already in use. Their introduction into actual practice extends the number of antibiotics and provides new options for difficult-to-treat infections. Thus, for new pharmaceutical compounds to be used in medicinal practice, it is important to investigate their biological activity, as well as other biological properties and adverse effects, such as phototoxicity. Full article

Understanding electron density migration along excited-state pathways in photochemical systems is critical for optimizing solar energy conversion processes. In this study, we investigate photoinduced electron transfer (PET) in a covalently linked donor–bridge–acceptor (D-B-A) system, where [Cu(I)-bis(1,10-phenanthroline)]⁺ acts as an electron donor, and anthraquinone, tethered to one of the phenanthroline ligands via a vibrationally active ethyne bridge, behaves as an electron acceptor. Visible transient absorption spectroscopy revealed the dynamic processes occurring in the excited state, including PET to the acceptor species. This was indicated by the spectral features of the anthraquinone radical anion that appeared on a timescale of 30 ps in polar solvents. Time-resolved infrared (TRIR) spectroscopy of the alkyne vibration (CC stretch) of the ethyne bridge provided insight into electronic structural changes in the metal-to-ligand charge transfer (MLCT) state and along the PET reaction coordinate. The observed spectral shift and enhanced transition dipole moment of the CC stretch demonstrated that there was already partial delocalization to the anthraquinone acceptor following MLCT excitation, verified by DFT calculations. An additional excited-state TRIR signal unrelated to the vibrational mode highlighted delocalization between the phenanthroline ligands in the MLCT state. This signal decayed and the CC stretch narrowed and shifted towards the ground-state frequency following PET, indicating a degree of localization onto the acceptor species. This study experimentally elucidates charge redistribution during PET in a Cu(I) diimine D-B-A system, yielding important information on the ligand design for optimizing PET reactions. Full article

Near-infrared (NIR) rhodamine dyes are pivotal for bioimaging due to the minimal tissue interference. Yet, their rational design is hindered by unreliable computational methods for excited-state property prediction. We benchmarked the time-dependent density functional theory (TDDFT) with the linear-response (LR) and state-specific (SS) solvation models across five functionals (CAM-B3LYP, M06-2X, ωB97X-D, B3LYP, MN15) and optimized the ground/excited states for 42 rhodamine derivatives. A robust linear calibration framework was established by connecting the computed and experimental wavelengths, which was rigorously validated through six-fold cross-validation. The key metrics included the mean absolute error (MAE) and R² to assess the prediction robustness. CAM-B3LYP combined with LR solvation achieved the highest accuracy (absorption: MAE = 6 nm, R² = 0.94; emission: MAE = 12 nm, R² = 0.72). By integrating the TDDFT with a calibrated linear-response solvation model, we achieved sub-12 nm accuracy in predicting the NIR fluorescence peaks. This framework enabled the rational design of nine novel rhodamine derivatives with emissions beyond 700 nm, offering a paradigm shift in bioimaging probe development. Full article

N-phenyl-1H-Indole-5-carboxamide (Ind-CA) exhibits previously unknown room-temperature phosphorescence (RTP) when immobilized in poly (vinyl alcohol) film (PVA film). High-fluorescence anisotropy of Ind-CA in PVA suggests that the fluorophores are strongly immobilized in a polymer matrix, while a relatively low (ca. 0.1) quantum yield indicates a strong non-radiative singlet excited state deactivation. With an increased triplet-state population, Ind-CA can be used for various phosphorescence studies. The room-temperature phosphorescence (RTP) capability of Ind-CA indicates that there is an intricate balance between RTP and the structure of the indole-containing luminophore, as an isomeric N-1H-indole-5-ylbenzamide (Ind-BA) does not show any appreciable levels of RTP. Moreover, the phosphorescence lifetime of Ind-CA is about two orders of magnitude longer than many other 5-substituted indoles. These results further highlight the prospects for the potential rational designs of small molecules with desired triplet-state configuration and RTP characteristics. Full article

Visible-light photoredox catalysis using biacetyl (BA) as a low-cost photosensitizer enables the efficient formation of triarylethylenes (TAEs) via a Mizoroki–Heck-type coupling. The reaction proceeds efficiently in acetonitrile upon blue LED irradiation under anaerobic conditions. Alternatively, supramolecular viscoelastic gels have also been explored as reaction media, allowing the possibility of working under aerobic atmosphere. Mechanistic investigations by means of transient absorption spectroscopy and quenching experiments support a charge-separated intermediate pathway. Reaction quantum yield measurements further validate the efficiency of BA, demonstrating its potential as an alternative to transition-metal catalysts. Overall, this work presents a sustainable and scalable strategy for TAEs synthesis, integrating photoredox catalysis with soft material engineering. These findings pave the way for broader applications in green chemistry and functional materials. Full article

IR-780 is a heptamethine cyanine dye that exhibits strong absorbance in the near-infrared region. Herein, we report IR-780 dye as a dual sensor for chromogenic cyanide detection and azide’s fluorogenic sensing in acetonitrile. Cyanide and hydroxide cause instant, dramatic color changes in the dye solution from green to yellow and dramatic spectral changes in the UV-Vis spectrum. The interaction of cyanide and hydroxide with the dye caused a dramatic decrease in the intensity of the strong absorption band at 780 nm and a concomitant band appearance at 435 nm. Other monovalent ions, including fluoride, chloride, bromide, iodide, dihydrogen phosphate, thiocyanate, acetate, and dihydrogen arsenate, caused no significant color or spectral changes. UV-Vis studies showed that the IR-780 dye is sensitive and selective to both ions. The detection limits for cyanide and azide are 0.39 µM and 0.50 µM, respectively. Interestingly, the IR-780 dye exhibited strong fluorescence at 535nm upon interaction with azide, while its initial emission at 809 nm was quenched. Both UV-Vis and fluorescence spectroscopy accomplished the detection of cyanide and azide using IR-780. Furthermore, the sensor’s effectiveness in fluorescence imaging of intracellular CN⁻ ions is demonstrated in live HeLa cells. Full article