Fig. 4: Depopulation of the S₁ excited state of BODIPY/Motor in different solvents.

a Time-resolved PL transients of BODIPY (red) and BODIPY/Motor (green) in toluene (open dots) and in acetone (filled dots) under 510 nm excitation. The PL transients were obtained by integrating the PL maps (Supplementary Fig. 16) in the \(520-600{{{{{\rm{nm}}}}}}\) spectral region, where PL of BODIPY occurs. The gray curves show the fits to exponential functions convoluted to the Gaussian apparatus function. The fitting parameters of the exponential functions are summarized in Supplementary Table 11. The black arrows depict the PL quenching upon attaching the motor core to BODIPY. The black open dots and curve depict the apparatus function at 510 nm and the fit to the Gaussian distribution, \(y=\frac{1}{\sqrt{2{{{{{\rm{\pi }}}}}}{\sigma }^{2}}}{e}^{-\frac{{t}^{2}}{2{\sigma }^{2}}}\) with \(\sigma=10{{{{{\rm{ps}}}}}}\). b Average PL lifetime of BODIPY/Motor as a function of the solvent polarity index. The polarity indexes and viscosity values of the solvents are summarized in Supplementary Table 12. The green line shows the best fit to a single-exponential function, \({\tau }_{{ave}}={{\exp }}(-{pt})\), with \(p=0.9\), to the average PL lifetime \({\tau }_{{ave}}\) as a function of the solvent polarity index \(p\).