Colorants, Volume 3, Issue 4 (December 2024) – 9 articles

Advancements in cellular imaging have significantly enhanced our understanding of membrane potential and Ca²⁺ dynamics, which are crucial for various cellular processes. Voltage-sensitive dyes (VSDs) are pivotal in this field, enabling non-invasive, high-resolution visualization of electrical activity in cells. This review discusses the various types of VSDs, including electrochromic, Förster Resonance Energy Transfer (FRET)-based, and Photoinduced Electron Transfer (PeT)-based dyes. VSDs are essential tools for studying mitochondrial activity and neuronal function and are frequently used in conjunction with Ca²⁺ indicators to elucidate the complex relationship between membrane potential and Ca²⁺ fluxes. The development of novel dyes with improved photostability and reduced toxicity continues to expand the potential of VSDs in biomedical research. This review underscores the importance of VSDs in advancing our understanding of cellular bioenergetics, signaling, and disease mechanisms. Full article

N-Phenylphenothiazine derivatives extended with various aryl groups were designed and synthesized. These derivatives have bent conformation in crystal and exhibit high solubility. Radical cations obtained by one-electron oxidation of these derivatives gave stable radical cations in solution and showed absorption in the near-infrared region. A radical cation was isolated as a stable salt, which exhibited heat resistance up to around 200 °C. A design strategy for radical cation-based near-infrared absorbing dyes, which are easily oxidized and stable not only as a solution but in solid form, is described. Full article

This study investigates the effects of varying CuO doping concentrations on the performance of titanium dioxide (TiO₂)-based or zinc oxide (ZnO)-based dye-sensitized solar cells (DSSCs). TiO₂ or ZnO mixed with CuO at different weight percentages (0–50 wt %) was employed as photoanodes in DSSCs, prepared via mechanical mixing. X-ray diffraction analysis revealed the structural changes, showing that as the CuO content increased in the hybrid, the CuO peaks (notably at 35.5° and 38.7°) became more prominent. Morphological and elemental characterizations were conducted using SEM and XRF, respectively. The solar cells were photosensitized by Vitis lasbrusca (V.L.) extract and N3 dye. The presence of anthocyanin molecules in the extracted V.L. was confirmed using UV-VIS and FTIR spectroscopy. The electrochemical characterization demonstrated optimal solar conversion efficiencies at a 20% doping level for both photosensitizers. Specifically, in the V.L. dye, TiO₂-CuO achieved a conversion efficiency of 7.18%, and ZnO-CuO reached 5.77%. In the N3 dye, TiO₂-CuO showed an efficiency of 11.34%, and ZnO-CuO, 9.55%. Notably, undoped photoanodes displayed a significantly lower photovoltaic performance: for V.L. dye, TiO₂ showed 1.12% and ZnO 0.87%; for N3 dye, TiO₂ showed 6.02% and ZnO 4.39%. Doping was therefore effective, yielding up to a seven-fold increase in performance in the case of V.L. with TiO₂, compared to undoped DSSCs. The results demonstrate that using the hybrid photoanode led to a considerable increase in performance compared to using only TiO₂ or ZnO photoanodes, highlighting the potential of DSSCs as sustainable energy sources. Full article

This work addresses the implementation of the co-sensitization technique to increase the energy efficiency of organic dye-sensitized solar cells (DSSCs). Fluorescent dyes derived from boron complexes— (BORANIL) and (BODIPY)— were successfully synthesized and used as co-sensitizers in different volume percentage ratios to verify the most effective concentration for photon capture through these sensitizers. The dyes were optically characterized using ultraviolet–visible spectroscopy (UV-VIS) and Fourier transform infrared (FTIR), analyzing them through the optical performance of each hybrid combination of dyes, an optimization of the photon collection capacity in the tests performed in a volume percentage ratio of 25:75 or 1:3. The morphology and surface roughness of the electrodes were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. Through electrochemical characterizations, it was found that the highest photovoltaic conversion efficiency was obtained with the ATH1005 (D) dye mixed with ATH032 (G) in the proportion of 25%:75% or DG 1:3, with efficiency (η) of 3.45%, against 2.43% and 1.90% for DG 1:1 and DG 3:1 cells, respectively. Cells with BODIPY dyes also present higher conversion efficiencies compared to BORANIL cells. The results corroborate the presentation of organic solar cells as a viable option for electricity generation. Full article

Hybrid pigments were obtained by combining zinc oxide with the anionic dye Congo red (CR), a breakthrough with significant environmental implications. By adjusting the ratio of solid mass to dye concentration, it is possible to obtain pigments with pink hues from a white solid (ZnO) through its adsorption of CR. The process involved using ZnO, prepared at 800 °C using cassava starch suspension as a suitable fuel. The oxide was characterized using XRD, SEM, and BET, and the results showed that the textural properties are typical of nanoparticles, with a size of 50.5 nm, a pore size of 3.48 nm, and a surface area of 3.03 nm, making it suitable for molecular dye removal. Controlling the adsorbent mass (in grams) and dye concentration (in mg L⁻¹) makes it possible to consistently produce hybrid pigments in various shades of pink that exhibit good thermal resistance. When dispersed in white waterborne paint, they are chemically stable in different solvents, have excellent painted surface coverage, and resist photochemical degradation. The results demonstrate technical feasibility and compatibility with the Sustainable Development Goals, particularly Goals 6, 11, 12, 14, 15, and 17, offering a promising solution for a more sustainable future. Full article

With the increasing awareness of socio-environmental issues, a global trend has emerged emphasizing the valorization of natural ingredients that promote health and well-being within sustainable production systems, such as microalgae-based carotenoids. Currently, little is understood about the correlation between biomass productivity and carotenoid content, which is a fundamental parameter for facilitating the immediate expansion of microalgae bioprocesses and ensuring the availability and industrial viability of these compounds. In this context, this study aims to investigate the carotenoid profile of Chlorella vulgaris through growth curve experiments conducted under photoautotrophic and heterotrophic regimes. Additionally, a trade-off analysis was performed for the production of carotenoids from microalgae. Carotenoids were quantified using high-performance liquid chromatography coupled with diode array and mass spectrometry detectors (HPLC-PDA-MS/MS). The performance of kinetic phases and energy demands across growth regimes was assessed to provide insights into production trade-offs. The results indicated that a total of 22 different carotenoids were identified in all the extracts. The all-trans-lutein and all-trans-β-carotene were the majority compounds. The total carotenoid content of Chlorella vulgaris revealed significant differences in the kinetic phases of carotenoid production, indicating that carotenoid volumetric production is only viable if the cultures are conducted until the log and stationary phases, based on the function of the biomass volumetric production (weight.volume⁻¹). Therefore, the best trade-off for the process was to provide photoautotrophic growth until the exponential phase (log). Under this condition, the maximum carotenoid and lutein content was 2921.70 µg.L⁻¹, reaching a maximum cell biomass of 1.46 g.L⁻¹. From an environmental/economic point of view, the energy demand was 7.74 kWh.L⁻¹. Finally, the scientific advances achieved in this study provide a holistic view of the influence of the main cultivation methods on the production of microalgae carotenoids, suggesting a viable initial direction for different industrial applications. Full article

(1) Background: This work evaluated the optical characterization of aqueous fluorescent chitosan-based carbon dots (or carbon nanoparticles CNPs) embedded in natural dye for potential functional packaging applications. Chitosan-based materials are nontoxic, biodegradable, biocompatible, bactericidal, and produced from renewable polymer sources. Anthocyanins are pigments of different colors with a large range of potential applications, such as in bioindicators and biomonitoring; (2) Methods: The CNPs were synthetized in aqueous solutions using chitosan as a carbon source. The natural dye was extracted from the leaves of Tradescantia pallida Purpurea in aqueous solutions. The fluorescence quantum efficiency (η) and fluorescence lifetime (τ) were determined using the mode-mismatched pump–probe thermal lens (TL) technique and time-resolved fluorescence lifetimes (TRFL) measurements, respectively; (3) Results: The η and τ were measured for CNPs embedded in natural dye solution at different concentrations (5.2, 12.09, and 21.57 mass percentage composition). The η and τ photophysical parameters obtained for CNPs embedded in natural dye were compared with those of other CNPs synthesized using different carbon sources, such as leaves, seeds, and protein; (4) Conclusions: Fluorescence spectra and time-resolved fluorescence measurements corroborate the TL results, and relatively high values of η were obtained for the CNP synthesized and embedded in natural dye. Full article

This perspective presents an account of the underlying features associated with the photofading of organic colorants. Photofading is commonly known to the scientific community as photodegradation or photooxidation, while in earlier times the more grandiose term “light fastness” was commonplace. This is a subject of immense diversity and significance, but there are many challenges to be faced when attempting mechanistic reasoning. The text is illustrated by descriptions of several systems taken from the scientific literature, together with anecdotes related to the principal researchers. The chemical challenges to be overcome in order to design photostable materials are outlined and reference is made to the natural world. It is stressed that the journal Colorants would welcome submissions in this field. Full article

Inorganic cool pigments are widely used as cooling agents in residential coatings due to their ability to achieve near-infrared reflectance. These coatings can be designed to exhibit a variety of colors independent of their reflectivity and absorption properties. Recent studies have highlighted the development of novel near-infrared (NIR) blue pigments, with an increasing emphasis on environmentally sustainable options that demonstrate high NIR reflectivity. This trend highlights the importance of creating novel and eco-friendly NIR reflective blue pigments. This study presents the synthesis of cobalt aluminates with varying concentrations of coloring ions (Co²⁺), achieved through the recycling of aluminum can seals via chemical precipitation. The formation of the spinel phase was confirmed through X-ray diffraction (XRD), and a colorimetric analysis was performed in the CIEL*a*b* color space. The synthesized pigments exhibited high near-infrared solar reflectance, with R% values ranging from 34 to 54%, indicating their potential as energy-efficient color pigments for use in coatings. Full article