| Abstract [eng] |
Viscosity plays a significant role on microscopic level in biosystems. It can determine the rate of diffusion-controlled processes, mass transport and intercellular molecular interactions. Atypical changes of intracellular microviscosity are associated with the development of diseases or pathologies. Thus, it is very important to monitor its variations within the cell. One of the most convenient methods to do that is by using viscosity-sensitive fluorophores, called fluorescent molecular rotors (FMRs). After FMR excitation intramolecular rotation occurs, which is dependent on the viscosity of the surroundings. Intramolecular rotation is fast in low viscosity solvents, which leads to an increased non-radiative relaxation, while in high viscosity solvents rotation is slow and fluorescence intensity, thus, increases. Besides the fluorescence intensity, quantum yield and decay time also increases. Boron-dipyrromethene (BODIPY) based FMRs are widely used as viscosity sensors. In between them, BODIPY-C10 and its other derivatives are the most popular molecular rotors. Their main advantages are easy functionalisation, photostability, monoexponential decay and relatively high molar extinction coefficient. However, their main drawback is absorption and fluorescence wavelengths. The most of the BODIPY based probes emit photons in a green spectral region. Red or near-infrared light is more desirable to obtain deeper tissue penetration and minimise light scattering when working with the biological samples. The main focus of this work is to characterise new BODIPY-based fluorescent molecular rotors and assess how changes in the molecular structure can influence their spectroscopic properties as well as sensitivity to the physical properties of a medium. Absorption and fluorescence emission spectra and fluorescence decays have been recorded to characterise spectroscopic properties of the samples. Dependences on polarity, viscosity, and temperature of the solvent were measured. The obtained results show that extension of the conjugated system in fluorophores results in a bathochromic shift of both absorption and fluorescence spectra. Moreover, it was found that addition of nitro group enhances viscosity sensitivity of fluorophores. Three new microviscosity probes (BP-Vinyl-NO2, BP-Ph-mMethyl-NO2, BP-Ph-oMethyl-NO2) were successfully investigated. Furthermore, it was shown that BP-Vinyl-NO2 fluorophore could be used to probe high microviscosity environments. |
