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.

To date, the concept of DNA-based asymmetric catalysis has been successfully applied to various synthetic transformations by way of hybrid catalysts involving either an intercalator or an integrated ligand anchored through supramolecular interactions. We report here a new anchoring strategy based on the well-known groove-binder Hoechst 33258. The interaction between calf thymus DNA (ct-DNA) and poly­[d­(A-T)2] with a series of Hoechst 33258-derived ligands was studied by UV–vis absorption spectroscopy, thermal melting analysis, fluorescence emission, CD spectroscopy, mass spectrometry, and molecular docking. The results clearly show that a groove-binding anchoring strategy can be envisioned for DNA-based asymmetric catalysis, offering additional mechanistic insight on how the intrinsic chirality of DNA can be transferred to a reaction product. Most importantly, this new anchoring strategy offers interesting compartmentalization possibilities and provides a new way to reverse the enantioselectivity outcome of a given reaction.