We investigate how strong optical coupling between Cy7.5 dye molecules and gold (Au) nanorod plasmonic nanoparticles can influence the photobleaching (photodegradation) behavior of the dye. In typical conditions, dye molecules degrade when exposed to light due to transitions to reactive triplet states. However, when the dye molecules are strongly coupled to the plasmonic resonance of the nanoparticles, we observed a reduction in the photobleaching rate. Moreover, we found a resonance‑like effect: there is an optimal number of dye molecules around each nanoparticle at which photobleaching is minimized. This effect arises because coupling changes the energy levels of the hybrid dye–nanoparticle system, enhancing the depopulation of the triplet state that leads to degradation. These findings suggest that carefully engineered strong coupling can improve the stability of organic dyes under illumination, which may benefit optoelectronic and photovoltaic applications where dye durability is important.
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