Understanding the dynamics of Fo''rster resonanceenergy transfer(FRET) in fluorophore-functionalized nanomaterials is critical fordeveloping and utilizing such materials in biomedical imaging andoptical sensing applications. However, structural dynamics of noncovalentlybound systems have a significant effect on the FRET properties affectingtheir applications in solutions. Here, we study the dynamics of theFRET in atomistic detail by disclosing the structural dynamics ofthe noncovalently bound azadioxotriangulenium dye (KU) and atomicallyprecise gold nanocluster (Au-25(p-MBA)(18), p-MBA = para-mercaptobenzoicacid) with a combination of experimental and computational methods.Two distinct subpopulations involved in the energy transfer processbetween the KU dye and the Au-25(p-MBA)(18) nanoclusters were resolved by time-resolved fluorescenceexperiments. Molecular dynamics simulations revealed that KU is boundto the surface of Au-25(p-MBA)(18) by interacting with the p-MBA ligands as a monomerand as a & pi;-& pi; stacked dimer where the center-to-centerdistance of the monomers to Au-25(p-MBA)(18) is separated by & SIM;0.2 nm, thus explaining the experimentalobservations. The ratio of the observed energy transfer rates wasin reasonably good agreement with the well-known 1/R (6) distance dependence for FRET. This work discloses thestructural dynamics of the noncovalently bound nanocluster-based systemin water solution, providing new insight into the dynamics and energytransfer mechanism of the fluorophore-functionalized gold nanoclusterat an atomistic level.
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