Highly Efficient Energy Transfer from Fluorescent Gold Nanoclusters to Organic J‑Aggregates

With an aim to understand the interaction between the inorganic and organic components in inorganic–organic hybrid nanostructured materials, we have designed and developed an inorganic–organic nanohybrid associate comprising inorganic fluorescent Au nanoclusters (NCs) and organic J-aggregates of a cyanine-based dye (S2165). The present system is quite interesting as in contrast to previously constructed nanohybrid systems where fluorescent quantum dots are integrated with an organic dye, the present system is developed using fluorescent gold nanoparticles and organic J-aggregates. The hybrid system has been characterized by spectroscopic and microscopic techniques. Steady-state absorption and emission and time-resolved fluorescence measurements have been performed to understand the optical properties of this hybrid system. In particular, the interparticle electronic interaction has been investigated by monitoring nonradiative energy transfer from fluorescent Au NCs (donor) to organic J-aggregates (acceptor). The fluorescence resonance energy transfer (FRET) event for the current system has been verified by various methods. ζ-Potential measurements and thermodynamic calculations have suggested that the interaction between Au NCs and J-aggregates in the hybrid associate is electrostatically driven. The analysis of data based on Förster theory has revealed that the energy transfer efficiency from inorganic to organic particles is very high. The observation of the high energy transfer efficiency in the present inorganic–organic hybrid associate is quite interesting as these results suggest that a metal-based system can also be very useful in designing a highly efficient light-harvesting system for various optoelectronic applications. Interestingly, both Au NCs and the Au–J-aggregate hybrid system are found to be cell-permeable and suitable for bioimaging studies. Additionally, because of the nontoxic nature of these systems, they can also be used in many biological applications.