Fluorescence is a phenomenon in which, due to a light or electromagnetic stimulus, an electron is excited, which passes from the ground state to an excited state. When transitioning back to the ground state, it emits light of a longer wavelength than it absorbed, which is reflected in the form of a fluorescent compound. The process of excitation and emission is easier to present with the Jablonski diagram, which with arrows shows the transitions between individual electronic states and also within them. Compounds that are able to undergo electronic transitions and subsequently fluoresce are called fluorophores. These include coumarins and their subspecies merocyanines. They are characterized by the presence of aromatic rings and a carbonyl group. Both require modifications of the structure by binding different substituents, which can also affect the enhancement or increase of fluorescence.
As part of the master's thesis, we synthesized compounds from the merocyanine group. It is an important group of fluorescent dyes that are used in the investigation of cell structures with the help of fluorescence microscopy, which allows us to discover the biochemical background of pathological conditions. Based on this, we can carry out the effective development of new, and above all, effective active substances.
When synthesizing, we used NMR spectroscopy to confirm the structure of the desired compounds. We successfully synthesized 4 compounds, namely 10(1), 10(2), 12 and 9. We recorded their absorption and emission spectra and measured their fluorescence. We also used them for fluorescence microscopy analysis, thus evaluating their suitability for labeling lipophilic structures. We found that all compounds are suitable for STED microscopy, that they are so little environmentally affected by the conditions in the molecule's environment and that they are photostable, thus confirming their suitability for cell labeling purposes.
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