Abstract
Photobleaching is a severely limiting factor in the optical study of single biomolecules. We investigate the photobleaching of rhodamine 6G (R6G) ensembles in poly(vinyl alcohol) (PVA) as a function of illumination time, excitation intensity, the presence of oxygen, and temperature. We observe nonexponential kinetics related to primary photobleaching through two dark statesthe triplet state and a radical anionand to secondary photobleaching after the optical excitation of those dark states. Reactions of the metastable states with oxygen can lead either to photoproducts or to a recovery of the ground state. Oxygen can therefore enhance or reduce photobleaching, depending on the experimental conditions. At low temperature, photobleaching is reduced although not completely suppressed. Despite the presence of the long-lived radical anion, we are able to observe single R6G molecules in PVA. At room temperature, only relatively bleaching-resistant molecules are resolved as individuals. At low temperature, the o...
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