Spectroscopic Methods of Ion Detection Using Fluorescent Probes

Dear Colleagues,

The universal development of civilisation currently observed in virtually every facet of our lives sadly also means that, as a species, we have been producing unprecedented amounts of harmful substances that have been released into the natural environment at a truly alarming rate. One evident example is the oversaturation with antibiotics utilised not only in medicine but also in animal husbandry, which ultimately end up in environmental circulation, polluting the water reservoirs of regions, countries, and even entire continents. Furthermore, modern advanced agriculture requires the widespread use of a variety of pesticides at practically every stage of a plant’s development. Unavoidably, a considerable portion of such substances spreads into the surrounding environment, polluting the soil, air, and, above all, water. And given the extreme rate at which the world’s population continues to grow, the need to protect said global water resources is now more pressing than ever. The list of related threats obviously goes on, which only underscores the need for more effective approaches to safeguarding our water resources, e.g., by employing a variety of spectroscopic methods.

In this Special Issue, we wish to draw the readers’ attention to the potential of fast detection methods in identifying various environmental pollutants by using the techniques of stationary and time-resolved fluorescence spectroscopy. In the context of the described problem, it is also necessary to develop new fluorescent probes that can serve as very efficient detectors of different polluting ions. It is our intention to demonstrate the wide spectrum of possible scientific applications of such new tools in conjunction with both newly developed and long-known compounds. The sheer number of such applications as well as the speed and detection accuracy that the methods facilitate are beyond most other available approaches, be it spectroscopic or utilising more rudimentary chemical analyses. Given the above, we need to continue identifying new chemical compounds, superior or equivalent to the ones already known in terms of their photophysical properties. As evidenced by the latest publication trends, one can observe a constantly growing interest in chemical compounds that, on the one hand, can produce interesting spectroscopic effects such as ESIPT, AIE, and TICT, and on the other, can be viably used to detect various environmental pollutants. At the same time, the rapid development of modern spectroscopic techniques provides the means needed to efficiently explore such research areas.

Determining the molecular mechanisms that affect the already known and newly discovered molecules will ultimately help us to better protect our common environment by identifying and describing new compounds capable of detecting, e.g., hypochlorite ions, as well as many others, such as Fe³⁺, Hg²⁺, Na⁺, K⁺, SO₄^2-, Fe²⁺, Cl^-, Cu²⁺, NO^3-, and Zn²⁺. This Special Issue explores topics related to the use of advanced fluorescence spectroscopy methods in conjunction with fluorescent probes to detect such ions. We are particularly interested in the fluorescence effects related to the turn-on and turn-off mechanisms as well as ratiometric studies relevant to the detection of changes in the local environment. Fluorescent probes interact with the analyte (ions present in a solution) and produce various emission effects, e.g., chelation-enhanced fluorescence (CHEF) in the case of turn-on probes, or chelation enhancement of emission quenching (CHEQ) in the case of turn-off probes. There are also a number of other mechanisms related to the electronic and molecular structures of the fluorescent probes and analytes, including excited-state intramolecular proton transfer (ESIPT), photoinduced electron transfer (PET), intraligand charge transfer (ICT), and ligand–metal charge transfer (LMCT or MLCT), to name but a few.

We invite authors to submit papers related to the aforementioned subject matter, particularly in conjunction with the uses of nanoparticles and other modern materials. We welcome both original studies on the subject and literature reviews summarising recent advances in the relevant area of study. Papers exploring basic spectroscopic methods that play a particularly important role in this context as well as more advanced approaches are encouraged. We would particularly like to feature studies utilising quantum chemical calculations, DFT, [TD]DFT, and crystallographic observations, but the inclusion of the same is naturally not required.

We also welcome papers conveying the results of biological studies related to particular molecules or complexes relevant to the overarching topic. Authors are particularly encouraged to submit studies where a description of a number of interesting spectroscopic properties is provided alongside an interesting theoretical discussion, a consideration of biological properties, or an otherwise multifaceted approach. We are happy to consider experimental spectroscopic studies, theoretical considerations, biological explorations, or any combination thereof.

Dr. Arkadiusz Matwijczuk
Guest Editor

Dr. Iwona Budziak-Wieczorek
Dr. Luca Ceresa
Guest Editor Assistants

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• CHEF, CHEQ, ESIPT, AIE, TICT, and similar fluorescence effects
• small-molecule additives (various small molecules, e.g., thiadiazoles, coumarins, hybrid systems of small molecules, molecular sensors)
• fluorescent properties of small molecules
• detection of ions: Fe³⁺, Hg²⁺, Na⁺, K⁺, SO4^2-, Fe²⁺, Cl^-, Cu²⁺, NO^3-, Zn²⁺, etc.
• fluorescent probes
• biological tests on antifungal properties
• molecular spectroscopy (electronic absorption and emission, fluorescence lifetime, TCSPC, molecular electronic transition spectroscopy, FTIR and Raman spectroscopy, circular dichroism (CD), differential scanning calorimetry (DSC), NMR and NMR imaging spectroscopy, SPR, FLIM, confocal microscopy, fluorescence microscopy, and other spectroscopic methods)
• various nanoparticle-based additives
• fluorescent and phosphorescent effects in solvents, amorphous forms, and crystals
• quantum mechanical calculations for the obtained systems/compositions
• molecular aggregation changing the fluorescent and phosphorescent properties of the tested systems