The fluorescence of phenylhydrazones: understanding the critical role of substituents in influencing the intensity of fluorescence and the evolution of emissive materials.

The overproduction of pollutants resulting from the development of industry causes the deposition of large amounts of toxic and carcinogenic substances, including heavy metals, in the aquatic ecosystem and other ecosystems. This is a civilisation problem of the present times, posing a serious threat to the natural environment, including humans. For this reason, it has recently become extremely important to develop effective methods to minimise the concentration of heavy metal ions in the aquatic systems and thus reduce their negative impact on the environment. One such technique is adsorption, which is believed to be an effective method of removing contaminants such as heavy metal ions from aqueous solutions. Looking at the available literature of the last few years, it can be concluded that adsorbents of natural origin are becoming more and more important. These are agricultural waste, all kinds of biomass, and waste from various industries. The study attempts to present and evaluate the sorption capacity of materials of natural origin, including oat bran, chitosan, alginate, tree bark, coconut fibre, and lignin. The use of such biosorbents is more friendly for the environment compared to their synthetic counterparts and perfectly fits the concept of sustainable development and the circular economy.

Three magnesium coordination compounds were obtained to explore the influence of carboxylate anions on the pattern of the formed hydrogen bonds. For their synthesis, various salts of magnesium carboxylic acid (formate, acetate, and propionate) were utilized. As an N-donor ligand, hexamethylenetetramine was employed. The supramolecular structures of the obtained compounds were determined and evaluated in Hirshfeld analysis. The length of the carbon chain of the used carboxylate anions has been proven to have a considerable impact on the self-organization of the supramolecular system by altering the three-dimensional net of the created hydrogen bonds. IR spectroscopy was used to characterize the obtained compounds, revealing significant differences between distinct systems. The thermal analysis of the investigated compounds also shows noticeable differences, demonstrating better stability of the systems containing formate anions.

A new polymorf of Schiff base (N-(4′-methoxybenzylidene)-4-aminobenzoic acid) and five of its distinct salts (chloride, bromide, nitrate, hydrosulfate and dihydrophosphate) were designed and synthesized. Detailed examinations were conducted to determine the structure and spectral properties of these compounds, employing methods like X-ray diffraction, as well as IR, UV-Vis and fluorescence spectroscopy. Interestingly, all the synthesized Schiff base salts displayed fluorescence when in solid state. However, the intensity of this fluorescence was found to differ, depending on the type of anion present within the structure. This result provides evidence that a strategy similar to supramolecular complexation can effectively be used to adjust the emission wavelength and control the intensity of fluorescence in the resulting solid materials.

In response to the trend toward sustainable management of by-products from the pulp and paper industry as well as plant waste, practical and economical methods are being developed to use them in a way that does not pose a threat to the environment. The main aim of the research was to study the possibility of using lignin and plant biomass as biosorbents for the removal of zinc ions from aqueous solutions. The secondary aim was to build an optimal multilayer system made of biosorbents selected during the research in order to obtain the highest sorption efficiency and to determine the best conditions of the sorption process. The effectiveness of zinc ion sorption was assessed using an appropriate combination of sorbents such as lignin, oat bran, rice husk, chitosan, pectin, sodium alginate, pine bark, coconut fiber and activated carbon, selected on the basis of literature data and the preliminary results of tests carried out using FTIR and AAS. The main component of the sorption system was lignin separated from black liquor. Results indicate that the best Zn sorption system was based on coconut fiber, lignin, and pine bark, for which the maximum sorption efficiency was 95%. The research also showed that the increase in the process temperature, the mass of biosorbents used and the alkaline pH are the factors that increase the efficiency of the sorption. It can be concluded that lignin and plant biomass can be used as ecological sorbents of zinc ions from water solutions. They are safe for the environment, produced from renewable sources, and are by-products or waste materials, which is part of the sustainable development and circular economy currently promoted in the EU.

The rational design of advanced functional materials with tailored fluorescence hinges on a profound understanding of the complex interplay between a molecule’s intrinsic structure and its local solid-state environment. This work systematically investigates these factors by employing a dual approach that combines targeted molecular synthesis with the subsequent modulation of the fluorophore’s properties within polymer matrices. First, a series of phenylhydrazone derivatives was synthesized, providing compounds with intense, solid-state fluorescence in the blue spectrum (421–494 nm). It was demonstrated that their photophysical properties were intricately linked to the substituent’s nature, which simultaneously modulated their intramolecular electron density and conformational rigidity while also governing their specific intermolecular packing in the solid state. Subsequently, we investigated the role of the supramolecular environment by embedding two fluorophores with distinct electronic profiles into electrospun poly (N-vinylpyrrolidone) (PVP) and polystyrene (PS) matrices. Our results reveal that the polymer matrix is not a passive host but an active component; it governs dye aggregation, induces significant blue shifts, and most critically, can impart exceptional thermal stability. Specifically, the PVP matrix shielded the embedded dyes from thermal quenching, maintaining robust fluorescence up to 100 °C. By combining molecular-level synthesis with matrix-level engineering, this work demonstrates a powerful strategy for the rational design of emissive materials, where properties like color and operational stability can be deliberately tuned for demanding applications in optoelectronics and sensing.