Colorants, Volume 4, Issue 2 (June 2025) – 5 articles

Aldehyde green, a dye first obtained by reacting fuchsine with acetaldehyde in 1862, consists of, according to analytical investigations carried out on a sample of this dye deposited in the Historical Dyestuff Collection of the Technical University Dresden and performed with liquid chromatography and high-resolution mass spectrometry, a mixture of various compounds in which the aniline groups of fuchsine are converted into quinaldine and dihydroquinaldine moieties. The dye owns its green color by two absorption bands in the visible range at 435 and 616 nm. Full article

The use of dyes as sensitizing agents to increase semiconductor activity is a strategy already adopted in the field of heterogeneous photocatalysis, but the compounds applied are noble metal-based and sometimes difficult to synthesize, which make it more expensive. In this work, it was discovered that methylene blue can perform such an effect on an iron molybdate functionalized with peroxo groups on the surface. This material, called MoOxoFe, was tested together with its analogue MoFe (produced without H₂O₂ in the synthesis) in the degradation of methylene blue. The rapid degradation of the dye led to the hypothesis of sensitization, which was investigated and proven by additional photocatalytic tests with sensitized material, MoOxoFe-MB, and spectroscopies, such as EPR and XPS. Full article

BODIPY (Boron-Dipyrromethene) dyes have emerged as versatile fluorescent probes in cellular imaging and therapeutic applications owing to their unique chemical properties, including high fluorescence quantum yield, strong extinction coefficients, and remarkable photostability. This review synthesizes the recent advancements in BODIPY dyes, focusing on their deployment in biological imaging and therapy. The exceptional ability of BODIPY dyes to selectively stain cellular structures enables precise visualization of lipids, proteins, and nucleic acids within live and tumor cells, thereby facilitating enhanced understanding of biochemical processes. Moreover, BODIPY derivatives are increasingly utilized in Photodynamic therapy (PDT) and Photothermal therapies (PTT) for targeting cancer cells, where their capability to generate cytotoxic reactive oxygen species upon light activation offers a promising approach to tumor treatment. Recently, BODIPY derivatives have been used for Boron Neutron Capture Therapy (BNCT) for various tumors, and it is a growing research field. Advancements in nanotechnology have allowed the fabrication of BODIPY dye-based nanomedicines, either alone or with the use of metallic nanoparticles as a matrix offering the development of a new class of bioimaging and theragnostic agents. This review also discusses innovative BODIPY-based formulations and strategies that amplify therapeutic efficacy while minimizing adverse effects, underscoring the potential of these dyes as integral components in next-generation diagnostic and therapeutic modalities. By summarizing current research and future perspectives, this review highlights the critical importance of BODIPY dyes in advancing the fields of cellular imaging and treatment methodologies. Full article

This perspective sets out to raise awareness about the chemical and photophysical properties of indigo, a highly distinguished colorant with an extraordinary history. Indigo, like many other dyes, was first extracted from plants at an inordinately low yield and at great ecological expense. Such was its popularity that indigo was among the first natural colorants to be synthesized in a laboratory before refinement and cost reduction resulted in its economical industrial-scale production. The color of indigo is highly characteristic but difficult to describe, since it falls at the blue/violet interface. It is a small, planar molecule with an exceptionally high degree of π-electron conjugation that pushes the absorption maximum to above 600 nm. Its structure helps explain the high level of photostability enjoyed by indigo, while recent spectroscopic studies have added to our understanding of the longevity of this emblematic colorant. The reversible formation of leuco-indigo increases the ways in which indigo can be used to add color to objects while helping to circumvent the effects of attack by free radicals. It is stressed that the journal Colorants would welcome submissions that describe the chemistry and/or spectroscopy of other representative colorants. Full article

Dyeing is a major contributor to pollution, with high concentrations of hydrolyzed dyes and electrolytes in its effluents. Recent studies suggest the possibility of dyeing cotton substrates with reactive dyes in an oil medium, reducing the need for electrolytes. This study evaluated the dyeing of cotton yarns with reactive Red 195 dye in an oil medium using crude and refined soybean oil. The method employed 75% oil and 25% water, with the oil recovered for reuse, significantly reducing water consumption and effluent generation. Dyeing with crude soybean oil showed higher color intensity than the conventional method and the use of refined soybean oil. Additionally, reducing electrolyte concentration from 75 to 18.75 g/L did not affect color intensity, yielding similar results to conventional aqueous dyeing. The dyed substrates were tested for washing, rubbing, and lightfastness, showing comparable performance to conventional methods. The dyeing followed pseudo-second-order kinetics, and the Freundlich isotherm model better fit the oil medium process. FTIR analysis revealed no changes in the functional groups on the yarn surface, and tensile strength tests showed similar results across methods. These findings indicate that oil medium dyeing can reduce electrolyte use, conserve water, and allow for oil reuse, demonstrating potential for industrial-scale application. Full article