Exploring viscosity, polarity and temperature sensitivity of BODIPY-based molecular rotors

Abstract

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.

A fluorogenic BODIPY molecular rotor as an apoptosis marker

“…These changes in the rate constants confirm that the observed increase in fluorescence efficiency at higher viscosity is due to the suppression of non-radiative processes as reported earlier for the parent BODIPY rotor. [36][37][38][39]47 As expected, we found a linear correlation of log f values versus log viscosity according to the Förster-Hoffmann equation with a slope of the plot of 0.6 ( Fig. 1c), in agreement with the literature data for BODIPY molecular rotors.…”

Molecular rotors report on changes in live cell plasma membrane microviscosity upon interaction with beta-amyloid aggregates

“…Our previous work has established that the calibration is still valid in non-polar mixtures, such as castor oil, and can be used for quantitative prediction of diffusion coefficients in lipid bilayers. 27 Importantly, BODIPY 1 provides lifetime vs viscosity calibration that is temperature independent, 26,42,43 i.e. is ideally suited for predictions of microviscosity in lipid membranes at variable temperature.…”

Regioisomeric BODIPY Benzodithiophene Dyads and Triads with Tunable Red Emission as Ratiometric Temperature and Viscosity Sensors

“…TICT rotors are promising viscosity probes because they exhibit emission enhancement due to restricted intramolecular rotation in solvents of increasing viscosity . Examples of ratiometric temperature and/or viscosity sensors based on TICT rotors involve fluorophores such as tetraphenylethylenes (TPE), indocyanines, porphyrins, 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY), arylboranes, N , N ‐dimethylaniline based compounds, and many others . Luminescent thermometers based on molecular rotors are being intensively investigated for temperature sensing of cellular microenvironments as well as of microfluidic devices .…”