Microviscosity is a key parameter controlling the rate of diffusion and reactions on the microscale. One of the most convenient tools for measuring microviscosity is by fluorescent viscosity sensors termed 'molecular rotors'. BODIPY-based molecular rotors in particular proved extremely useful in combination with fluorescence lifetime imaging microscopy, for providing quantitative viscosity maps of living cells as well as measuring dynamic changes in viscosity over time. In this work, we investigate several new BODIPY-based molecular rotors with the aim of improving on the current viscosity sensing capabilities and understanding how the structure of the fluorophore is related to its function. We demonstrate that due to subtle structural changes, BODIPY-based molecular rotors may become sensitive to temperature and polarity of their environment, as well as to viscosity, and provide a photophysical model explaining the nature of this sensitivity. Our data suggests that a thorough understanding of the photophysics of any new molecular rotor, in environments of different viscosity, temperature and polarity, is a must before moving on to applications in viscosity sensing.
Eleven formyl-containing BODIPY dyes were prepared by means of either the Liebeskind-Srogl cross-coupling reaction or the Vilsmeier reaction. These dyes were used as components in the Passerini reaction to give highly substituted BODIPY dyes. A joined spectroscopic and theoretical characterization of the synthesized compounds was conducted to unravel the impact of the structural rigidity/flexibility on the photophysical signatures. These dyes were tested as fluorescent trackers for phagocytosis. Additionally, they proved to be useful to stain different blood cells with an intense and stable signal at a very low exposure time.
A series of complex boronic acids
were prepared through multicomponent
reactions (MCRs). Both Passerini and Ugi MCRs were carried out in
which one component was an arylboronic acid. The resulting highly
functionalized boronic acids participated efficiently in the Liebeskind–Srogl
cross-coupling reaction with meso-methylthioBODIPY
derivatives to yield complex borondipyrromethene (BODIPY) dyes in
good yields. The joined spectroscopic and computational study points
out the deep impact of the arylated chromophoric position on the photophysical
signatures. Thus, unconstrained aryls grafted at the meso position
did not sway the spectral band positions but switched on new nonradiative
relaxation channels, whereas additional arylation at the opposite
α-pyrrolic position softened such fluorescence quenching and
shifted the emission to the red-edge of the visible spectrum. The
conducted biological analysis revealed that peripheral blood mononuclear
cells incubated with these new compounds showed reduced cytotoxicity
and retained their normal activities. Additionally, the dyes remained
stable inside the cells after 24 h of incubation. These results demonstrated
that these novel fluorescent probes based on BODIPY can be applied
for cell imaging and analysis, expanding their applications.
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