Fig 1.

A) Schematic showing the concept behind FMRs, adapted from Levitt et al [13]. Normal absorption and fluorescence occurs when rotation is restricted, but a non-radiative pathway can be accessed when rotation is free. This influences the fluorescence lifetime. Note that while most FMRs are planar in the ground state, BODIPY rotors such as FMR-1 and FMR-2 are not [7]. B) Diagram of confocal FLIM microscope set-up using the scanning to get position and timing information. PMT: photomultiplier tube, TCSPC: time-correlated single photon counting. C) Diagram of the step involved in mitochondrial extraction.