Photobleaching of randomly rotating fluorescently decorated particles

Randomly rotating particles that have been isotropically labeled with rigidly linked fluorophores will undergo non-isotropic (patchy) photobleaching under illumination due to the dipole coupling of fluorophores with light. For a rotational diffusion rate D of the particle and a photobleaching time scale $τ$ of the fluorophores, the dynamics of this process are characterized by the dimensionless combination $Dτ$⁠. We find significant interparticle fluctuations at intermediate $Dτ$⁠. These fluctuations vanish at both large and small $Dτ$ or at small or large elapsed times t. Associated with these fluctuations between particles, we also observe transient non-monotonicities of the brightness of individual particles. These non-monotonicities can be as much as 20% of the original brightness. We show that these novel photobleach-fluctuations dominate over variability of single-fluorophore orientation when there are at least 10³ fluorophores on individual particles.