Photochem

4-Dimethylamino-2′-hydroxy chalcone (DHC) 1 is an important natural compound that is nearly non-fluorescent in solution but highly fluorescent in its crystalline state. At room temperature, the weak fluorescence from the DHC solution is exclusively from its keto tautomer, without notable contribution from its enol tautomer. By using low-temperature fluorescence, the study found that the enol emission could be detected upon cooling with liquid N₂ in a protic solvent (e.g., EtOH). This led to observation of the fluorescence vibronic structure of enol tautomer, in addition to its enol emission λ_em ≈ 473 nm that is well separated from its keto tautomer emission (λ_em ≈ 600 nm). By freezing DHC in a solvent matrix, the study revealed the fluorescent characteristics of a single molecule in a rigid environment. Further comparison of DHC in a solvent matrix and crystalline state disclosed that the emission of crystalline DHC was primarily from the keto tautomer, along with some minor contribution from the enol tautomer, despite the tight packing environment in the crystalline state. Full article

TiO₂ is normally a preferred photocatalyst; however, its photocatalytic performance is constrained by its low surface area, wide band gap, and high electron–hole pair recombination rates. The objective of this study was to optimize the photocatalytic efficiency of TiO₂ by impregnating it onto activated carbon derived from Senegalia mellifera biomass. The quantitative study involved synthesizing TiO₂ using the precipitation technique and preparing AC through both chemical and physical activation methods. The prepared AC samples were impregnated with TiO₂ NPs using the wet impregnation method. The physicochemical properties of the samples were examined using several characterization techniques, namely, FTIR, EDS, Raman, UV reflectance, STA, SEM, and BET. The photocatalytic efficiency of AC/TiO₂ composites was evaluated through methyl orange degradation. The results showed significant improvement in photocatalytic performance when TiO₂ was supported on AC. The modified photocatalyst exhibited enhanced surface area, thus increased active sites for photocatalysis, improving electron–hole separation and reducing recombination. The 50%CO₂/AC-0.5TiO₂ composite demonstrated superior photocatalytic activity under both UV and visible light irradiation. It showed 52.1% MO removal under visible light and 76.1% MO removal under UV light. The study concludes that biomass-derived AC/TiO₂ composites present a promising, cost-effective and sustainable approach of enhancing photocatalytic activities. Full article

The increasing prevalence of antimicrobial resistance, together with recurring infectious disease outbreaks, has intensified the need for alternative strategies to control microbial infections beyond conventional antibiotic therapies. Antimicrobial photodynamic therapy has emerged as a promising non-antibiotic approach in which light-activated photosensitising compounds generate reactive oxygen species that induce oxidative damage to microbial cells. Plant-derived photosensitisers have attracted increasing attention due to their structural diversity, biocompatibility, natural abundance, and potential for sustainability. Natural compounds such as curcumin, hypericin, chlorophyll derivatives, flavonoids, anthraquinones, and riboflavin exhibit favourable photochemical properties that enable efficient production of reactive oxygen species upon irradiation with visible light. Through radical- and singlet-oxygen-mediated photochemical pathways, these molecules exhibit broad-spectrum antimicrobial activity against bacteria, fungi, viruses, and biofilm-associated microorganisms. This review examines the photophysical properties and mechanisms of reactive oxygen species generation associated with plant-derived photosensitisers, together with key factors influencing their antimicrobial performance. Recent advances in nanocarrier-based delivery systems, dual-wavelength activation strategies, and synergistic combination therapies are also discussed for their potential to improve photostability, enhance reactive oxygen species generation, and increase microbial inactivation efficiency. Finally, current progress, challenges, and future research directions for advancing plant-derived photosensitisers in antimicrobial photodynamic therapy are discussed. Full article

Seminaphtofluorones (SNAFRs) are a family of benzannulated xanthene dyes that exhibit strong fluorescence in both neutral and anionic states and can reach emission wavelengths in the deep-red to near-infrared region. Their optical response is highly sensitive to regioisomerism and functionalization, making them attractive candidates for systematic structure–property investigations. Here, we computed the photophysical properties of six SNAFR regioisomers for both neutral and anionic species and correlate the calculated results with available experimental data. From the six dyes, we further chose two of them, SNAFR4 and SNAFR6, to further investigate how phenyl-ring functionalization modulates SNAFR properties by introducing methyl (–CH₃) and carboxyl (–COOH) substituents at the ortho (o), meta (m), and para (p) positions. The calculations indicate that substitution induces measurable changes in geometries, as well as in excitation and emission energies, with particularly pronounced effects for the anionic derivatives. Overall, these results provide a computational framework for the rational tuning of SNAFRs’ optical properties and the design of derivatives with tailored optical characteristics for fluorescence imaging and applications in photodynamic therapy. Full article

Singlet oxygen (¹O₂) is a key mediator in photodynamic therapy (PDT), and its generation and reactivity in biological systems have been extensively studied. It has been shown that laser radiation at near-infrared (NIR) regions can be used to directly generate ¹O₂. In this work, we investigated photosensitizer-free ¹O₂ generation using an original all-fiber pulsed laser operating at 1066 nm and 1241 nm and evaluated its impact on mitochondrial activity in U-87 MG glioblastoma cells. Singlet oxygen was evaluated using the 1,3-diphenylisobenzofuran (DPBF) chemical probe and confirmed with argon-purging controls, demonstrating clear oxygen- and wavelength-dependent effects. Laser irradiation of glioblastoma cells demonstrated distinct effects depending on the wavelength, although decrease in cellular metabolic activity was observed in both cases. Interestingly, some inhibitory effect was also observed when the culture medium was pre-irradiated at 1241 nm and subsequently added to intact cells. These results demonstrate that laser radiation at both studied wavelengths can elicit measurable biological effects, although the relative efficiency in chemical versus cellular systems varies. Collectively, these findings provide a foundation for further systematic studies of wavelength-specific NIR interactions with cellular and molecular components in biological environments. Full article

All forms of neural communications, from cognition to emotion, are regulated by neurotransmitters, which are otherwise the chemical language of the brain. Precise detection of these neurotransmitters is essential for the perception of neurophysiology and diagnosis of neurodegenerative diseases as well. Among the existing techniques for the detection of these molecules, fluorescence sensing is evolving as a powerful approach in terms of high sensitivity, rapid response, and real-time visualization of the chemical events occurring in the neural system. In recent years, nanomaterials have transformed this field by integrating tunable optical properties, excellent photostability, and modifiable surface chemistry into biocompatible nanostructures. We summarize the recent advances of these architectures to show how the material type and dimensionality, as well as the surface functionality, play roles in sensing through the mechanisms of Förster resonance energy transfer (FRET), photoinduced electron transfer (PET), inner filter effect (IFE), and aggregation-induced emission (AIE). The discussion has also been extended to the correlation of fluorescence modulation with the selectivity and sensitivity in the mechanism-to-function relationship. The potential utility of such innovative technologies, including artificial intelligence, spectral deconvolution analysis via big data algorithms, and chip-integrated sensing, was explored as a means to enable real-time neurochemical detection. This converging area of nanotechnology and neuroscience leaves a mark not just in analytical accuracy, but also parallels human brain rhythms. Full article

The direct thermal conversion of thiourea on fluorine-doped tin oxide (FTO) substrates is widely used to fabricate sulfur-doped carbon nitride (S-CN) photoelectrodes; however, substrate-induced effects often contribute to photoelectrochemical response. Here, we show that the sulfurization of FTO during thermal treatment leads to the in-situ formation of a tin sulfide underlayer, mainly SnS₂, which significantly contributes to the observed photoresponse. A systematic study as a function of temperature reveals that the formation of sulfur-doped carbon nitride and tin sulfide occurs within a similar temperature window, making temperature control alone insufficient to suppress substrate sulfurization. To overcome this limitation, a thin compact carbon nitride interlayer synthesized from melamine was introduced between the FTO substrate and the S-CN film. This interlayer effectively prevents tin sulfide formation and enables the growth of an adherent S-CN film. The resulting photoanodes exhibit stable photoelectrochemical performance toward water oxidation under alkaline conditions (1M KOH), with an onset potential of ~+0.4 V vs. RHE and stable photocurrents up to 40 μA·cm⁻² under AM 1.5G illumination. Electrochemical impedance spectroscopy confirms that the compact carbon nitride interlayer also acts as an effective charge-blocking barrier. This work provides a reliable strategy to avoid substrate-induced artifacts and establishes clear design guidelines to prepare truly sulfur-doped carbon nitride photoelectrodes. Full article

Hollow fibers (HFs) have recently gained attention as an advantageous photocatalyst immobilizer for heterogeneous catalysis. Depending on their fabrication method, they can come up, or not, with a porous network within their structure. In this case, they are sometimes referred to as membranes, although they are not applied in liquid flow applications as filters. This work provides a concise overview of all the studies encountered in the literature on photocatalytic hollow fibers (HFs) and hollow fiber membranes (HFMs), clarifying the prevailing confusion about the topic. All publications are categorized with respect to their reported applications in batch liquid, flow, or gas experiments. Full article

Our recent work has focused on red light-mediated photoreduction of p-benzoquinones and both o-, and p-naphthoquinones using methylene blue and the chlorophyll metabolite, pheophorbide A as photosensitizers. Photoreduction of biologically relevant quinones mimics photoreduction of plastoquinone by chlorophyll in photosynthesis. We examined photo-oxidation and photoreduction reactions of catechols because their oxidation to o-quinones by reactive oxygen species is implicated in protein damage in neurodegeneration. Photo-oxidation of catecholamines including dopamine, epinephrine and norepinephrine required red light, methylene blue or pheophorbide A, and molecular oxygen. Their cyclized oxidation products, aminochrome, adrenochrome and noradrenochrome, were detected by UV/visible spectroscopy. Hydrogen peroxide was generated during photo-oxidation by singlet oxygen-dependent oxidation of catecholamines. Inclusion of tertiary amine electron donors decreased cyclized products but did not affect hydrogen peroxide yield consistent with concurrent photo-oxidation followed by photoreduction of the o-quinone intermediate. Unreacted dopamine and norepinephrine were quantified using 3-hydroxyphenyl boronic acid following photochemical reactions. Dopamine and norepinephrine boronate esters absorb at 417 and 550 nm. Photo-oxidation of dihydroxycaffeic acid and dihydroxyphenyl acetic acid was also evaluated by detecting their boronate esters at 475 nm. We hypothesize that photoreduction of transient o-quinones by the combination of red light and dietary chlorophyll metabolites may be a path to limit protein damage and to recycle catechol antioxidants. Full article

Gastrointestinal (GI) malignancies have caused tremendous disease burden around the world; however, conventional therapy strategies, such as radiotherapy, chemotherapy, and immunotherapy, have achieved limited efficacy in the diagnosis and treatment. In further exploration of GI tumors, the complexity and heterogeneity of the tumor microenvironment (TME) have been increasingly recognized. Appropriate strategies to modulate the TME are necessary to enhance the therapeutic effect. Photosensitizers (PSs) are chemical substances that are activated at specific wavelengths of light to initiate photodynamic effects. Nanotechnology provides a platform for the targeted delivery of PSs and small-molecule drugs, enabling precise targeting and remodeling of the TME. In this review, we summarize the principles and mechanisms of photochemical reactions and elaborate on the effect of photochemical nanoplatforms in modulating the TME of GI tumors. Finally, we discuss the potential value of photochemical nanoplatforms for diagnosing GI malignancies. Full article

Time-resolved (TR) resonance Raman (RR) spectroscopy with continuous-wave excitation is a fundamental technique that has contributed substantially to the understanding of the structure and dynamics of retinal proteins. However, the underlying principles were developed about fifty years ago for instrumentation that is hardly in use anymore. Thus, the adaptation of the technique to the current state-of-the-art equipment is needed to satisfy the increasing demand for the spectroscopic characterization of novel retinal proteins. In this work, we focus on pump–probe TR RR experiments with a confocal spectrometer using a rotating cell. We define the parameters ensuring fresh-sample condition and the photochemical innocence of the probe beam as a prerequisite for studying retinal proteins that undergo a cyclic photoinduced reaction sequence. For the measurements of intermediate states and reaction kinetics, pump–probe experiments are required in which the two laser beams hit the flowing sample with a defined but variable delay time. An appropriate set-up for such two-beam experiments with a confocal spectrometer is proposed and tested in TR experiments of bacteriorhodopsin. The comparison with the results obtained with classical slit spectrometers using a 90-degree scattering illustrates the advantages and disadvantages of the confocal arrangement. It is shown that modern confocal spectrometers substantially decrease the spectra acquisition time but require a more demanding optical set-up. Furthermore, the extent of photoconversion by the pump beam is lower than for the 90-degree-scattering arrangement, which reduces the accuracy of kinetic measurements. Full article

The transition to more sustainable models of production and consumption has encouraged the scientific community to seek innovative solutions that promote environmental responsibility and reduce waste. The cosmetic industry, in particular, has increasingly invested in natural and eco-friendly ingredients as alternatives to synthetic and environmentally harmful components. In this context, plant-derived bioactive compounds with antioxidant and anti-inflammatory potential have gained attention for their ability to enhance photoprotection and reduce the concentration of conventional ultraviolet (UV) filters in sunscreens. Humulus lupulus L. (hop), a plant traditionally used in the brewing industry, generates large amounts of organic waste after the beer production process, especially through the dry-hopping technique. Despite often being discarded, this residual biomass retains important secondary metabolites with high biological value. Our investigation researched the sustainable valorization of hop brewing residues as a source of bioactive compounds for the development of more natural photoprotective products. We performed HLPC-MS/MS analysis and confirmed the presence of α-acids in both pure and reused hop material extracts, while a xanthohumol-like prenylated flavonoid was tentatively detected exclusively in the extract obtained from reused hop extract. In vitro tests demonstrated that sunscreens containing extract obtained from reused material significantly increased the sun protection factor (SPF) without negatively altering the critical wavelength when water was used as the solvent. None of the samples developed higher UVAPF values compared to the control. Our investigation, to the best of our knowledge, constitutes the first successful proof of concept demonstrating the use of both pure (non-reused) and reused hop material extracts as functional photoprotective adjuvants in sunscreen formulations evaluated by a robust, standardized in vitro methodology. This work highlights the dual benefit of reducing industrial waste and developing more sustainable, consumer-friendly cosmetic products. Full article

Sosnovsky’s hogweed (Heracleum sosnowskyi Manden.) is an invasive plant species widely distributed across Eastern Europe and Russia that poses a serious threat to human health due to its pronounced phototoxic properties. Contact with the plant sap followed by exposure to solar ultraviolet (UV) radiation frequently results in phytophotodermatitis, which is characterized by erythema, blistering, ulceration, and persistent hyperpigmentation. The development of these photochemical injuries—most notably furanocoumarins—act as potent photosensitizers and induce cellular and DNA damage upon UV activation. This review provides an integrated overview of the geographical spread and invasiveness of H. sosnowskyi, the chemical composition of its biologically active metabolites, and the molecular mechanisms underlying hogweed-induced skin injury. Particular emphasis is placed on the photochemical transformations of furanocoumarins, including psoralens and their photooxidation products, such as 1,2-dioxetanes, which generate reactive oxygen species and DNA crosslinks. In addition, the review examines other compounds derived from hogweed biomass—including furan derivatives, aromatic compounds, fatty acids, sterols, and their oxidative products—that may contribute to phototoxic and cytotoxic effects. Clinical manifestations of hogweed-induced burns, their classification, symptomatology, and current therapeutic approaches are critically discussed, highlighting the absence of standardized treatment guidelines. Rather than serving as a purely clinical or botanical survey, this review frames Sosnovsky’s hogweed injury as a solar-light-activated photochemical hazard, tracing the sequence from environmental sunlight exposure through molecular photochemistry to biological tissue damage. By integrating chemical, biological, and dermatological perspectives, the review aims to clarify injury mechanisms and support the development of more effective preventive and mitigation strategies under real-world exposure conditions. Full article

We report the use of σ-alkynyl d⁶ electron-rich transition metal complexes as electron-releasing end-groups in octupolar molecules designed for nonlinear optical (NLO) applications, specifically, N,N′,N″-triarylisocyanurates (5,7,8,10,12) and 1,3,5-triarylbenzenes (6,9,11) functionalized by Fe(II) and Ru(II) organometallic moieties, and their NLO properties, as assessed by hyper-Rayleigh scattering (HRS) and Z-scan. The redox properties are briefly investigated through isolation of the corresponding Fe(III) trications 5[PF₆]₃ and 6[PF₆]₃. The second-harmonic generation (SHG) or two-photon absorption (2PA) performance of the Fe(II) and Ru(II) parents is compared with the help of TD-DFT calculations performed on models. Comparison with tris-ferrocenyl isocyanurate 4 reveals that the σ-connection of the metallic centers to the π-manifold is superior to the η⁵-connection for enhancing NLO properties. The positive effect of organometallic end-groups on NLO properties relative to purely organic electron-releasing substituents is established. The mechanism by which NLO enhancement occurs is complex and possibly connected to the polarizable π-electrons in the ligands surrounding the metal alkynyl units, but in most cases, the observed NLO enhancement must arise from the transition metal centers interacting with the central π-manifold. Full article

Synthesizing natural substances has always been a significant challenge for organic chemists. The key to a successful total synthesis lies in utilizing reactions that generate molecular complexity with high stereocontrol. Photochemical reactions offer immense potential in this regard, though their complex mechanisms require careful mastery. This review explores recent examples from the literature where light-mediated reactions are crucial, often irreplaceable by thermal alternatives. The manuscript is organized by different photochemical processes, each introduced with relevant background. This review does not offer a complete analysis of all recent light-assisted syntheses; rather, it offers a glimpse into the growing trend of using photo-driven transformations to address significant synthetic challenges. Full article

Titanium dioxide (TiO₂) thin films were deposited by DC magnetron sputtering and subsequently treated in hot water at 50, 70, and 95 °C for 72 h to investigate the influence of low temperature on their structural optical and functional properties. XRD analysis revealed a progressive transformation from amorphous to anatase phase with increasing treatment temperature, accompanied by an increase in crystallite size from 5.2 to 15.1 nm. FT-IR spectroscopy confirmed enhanced surface hydroxylation and contact angle measurements showed a decrease from 77.4° to 19.7°, indicating a significant improvement in superior wettability. The transmittance spectroscopy revealed a slight narrowing of the optical band gap from 3.34 to 3.21 eV, consistent with improved visible-light absorption. Photocatalytic tests using the Resazurin indicator demonstrated that the film treated at 95 °C exhibited the highest activity, achieving a bleaching time of 245 s three times faster than treated at 50 °C and twice as fast as treated at 70 °C. Under low-intensity solar irradiation, the same sample achieved complete E. coli inactivation within 90 min. These improvements are attributed to increased crystallinity, surface hydroxyl density, and enhanced ROS generation. Overall, this study demonstrates that mild hot-water treatment is an effective, substrate-friendly route to enhance TiO₂ film wettability and multifunctional performance, enabling the fabrication of self-cleaning and antibacterial coatings on fragile materials such as plastics and textiles. Full article

The increasing atmospheric concentration of CO₂ is a major contributor to global climate change, underscoring the urgent need for effective strategies to convert CO₂ into value-added products. In this sense, a composite was successfully synthesized by combining clinoptilolite zeolite (CZ) with varying amounts of copper oxide (CuO-1% and 10%) for CO₂ photoreduction. The composites were characterized using insightful techniques, including XRD, nitrogen physisorption, DRS, and SEM. The results confirmed the incorporation and dispersion of CuO within the CZ support. The XRD analysis revealed characteristic crystalline CuO peaks. Despite the low surface area (<15 m²·g⁻¹) and macroporous nature of the samples, EDS imaging revealed an effective and homogeneous dispersion of CuO, indicating efficient surface distribution. UV–Vis diffuse reflectance spectroscopy revealed band gap energies of 3.30 eV (CZ), 3.38 eV (1%-CuO/CZ), and 1.75 eV (10%-CuO/CZ), highlighting the pronounced electronic changes resulting from CuO incorporation. Photocatalytic tests conducted under UVC irradiation (λ = 254 nm) revealed that 10%-CuO/CZ exhibited the highest CO and CH₄ production, 35 µmol·g⁻¹ and 3.6 µmol·g⁻¹, respectively. The composite also delivered the highest CO productivity (5.91 µmol·g⁻¹·h⁻¹), approximately 3.5 times that of pristine CZ, in addition to achieving the highest CH₄ productivity (0.60 µmol·g⁻¹·h⁻¹). Furthermore, turnover frequency (TOF) analysis normalized per Cu site revealed that CuO incorporation not only enhances total productivity but also improves the intrinsic catalytic efficiency of the active copper centers. Overall, the synthesized composites demonstrate promising potential for CO₂ photoreduction, driven by synergistic structural, electronic, and morphological features. Full article

The photochemistry of transition metal complexes has been crucial for the development of many fundamental topics, as well as to pave the way for several important applications. However, in most cases, photoactive transition metal complexes involved precious metals, with luminescent ruthenium polypyridine complexes playing the dominant role. Developing photoactive species based on earth-abundant metals is highly important for fundamental and applicative reasons. Iron is one of the most abundant metals on Earth’s crust, so luminescent iron complexes are highly desired. The recent search for iron complexes with long-lived and luminescent excited states is here presented, including Fe(II) species with metal-to-ligand charge transfer (MLCT) excited states and Fe(III) species with luminescent ligand-to-metal charge transfer (LMCT) states. The excited-state equilibration approach to prolong the luminescence lifetimes of Fe(III) compounds in multichromophoric species is also discussed. This latter approach can increase the possibility of luminescent iron complexes being involved in bimolecular processes as well as in photoinduced electron and energy transfer at interfaces, which is relevant for many applications. Full article

Two-dimensional (2D) metal halide perovskites have attracted considerable interest for their markedly improved environmental stability and versatile compositional tunability compared to their three-dimensional (3D) counterparts. Nevertheless, the anisotropic charge transport caused by insulating organic spacers often leads to inefficient charge transport and limiting device performance. Precise control over crystallographic orientation, particularly achieving vertical alignment of the inorganic layers, is essential to facilitate out-of-plane charge transport and enhance device efficiency. This review systematically summarizes recent advances in understanding and controlling the crystallographic orientation of 2D perovskites, emphasizing manipulating strategies such as processing optimization, composition engineering, spacer design, solvent selection, and additive assistance to promote vertical alignment of inorganic layers and improve interlayer charge transport. We also discuss the influence of phase distribution, quantum well width, and crystal growth kinetics on device performance. Finally, we outline prevailing challenges and future opportunities for achieving the ideal microstructure and high-efficiency 2D perovskite solar cells. Full article