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Theodore Goodson1

1, Univ of Michigan, Ann Arbor, Michigan, United States

Metal nanoclusters are now excellent candidates for applications in optical limiting and other nonlinear optical processes. The use of nanoclusters as building blocks for larger structures has found new interest due to the unique optical and electronic properties. In this presentation it will be shown that one can synthesize chromophore-Au25 nanocluster oligomers and investigate their linear and nonlinear optical properties. The chromophore-Au25 nanocluster oligomers were separated by polyacrylamide gel electrophoresis and characterized by matrix assisted laser desorption ionization mass spectrometry and scanning transmission electron microscopy imaging. The linear optical properties of the systems were investigated by steady state UV-vis absorption and fluorescence spectroscopy. The chromophore-Au25 nanocluster oligomers showed increased oscillator strength and transition dipole moment compared to single Au25 nanoclusters. Energy transfer from the chromophore 4,4’-thiodibenzenethiol (TBT) to the metal cluster was observed in the chromophore-Au25 nanocluster dimer system. The excited state and fluorescence dynamics were investigated by transient absorption spectroscopy, time-resolved fluorescence up-conversion and time-correlated single photon counting. The chromophore-Au25 nanocluster oligomers have a long-lived surface state, due to the contribution of energy transfer by two nanocluster cores. The two-photon absorption cross sections of the chromophore-Au25 nanocluster oligomers showed an increasing enhancement trend with increasing oligomer length. An enhancement factor of up to 68 times was found compared to single Au25 nanoclusters. These Chromophore-Au-Chromophore oligomers are excellent candidates for applications in nonlinear optics.

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