Optically-active nanoparticles derived from a group of uniform materials based on organic salts (GUMBOS) offer exciting possibilities for advances in optoelectronics due to their highly diverse functional and photodynamic properties. We have used ultrafast pump-probe transient absorption (TA) spectroscopy to study size-selected crystalline nanoparticles of tris(2,2'-bipyridyl) ruthenium(II) and (pentafluoroethylsulfonyl) imide, or [Ru(bipy)3][BETI] 2, in aqueous colloidal suspensions, with the results compared to corresponding measurements of aqueous Ru(bipy)3Cl2 solutions. Time-resolved TA spectra from Ru(bipy)3Cl2 in water are described by two excited-state lifetimes corresponding to the metal-to-ligand charge-transfer (MLCT) complex and the metal-centered (MC) complex. Time-resolved TA spectra from size-selected [Ru(bipy)3][BETI]2 nanoparticles are described by three excited-state lifetimes corresponding to the MLCT complex, the MC complex, and intermolecular energy transfer (IMET). Representative TA results from 23 nm nanoparticles are shown in Figure 1.  These results suggest that IMET occurs rapidly, while the crystalline material confines molecular motion to lengthen excited-state lifetimes. Additionally, large acoustic phonon oscillations in the TA spectra persist during the entire excited-state relaxation timescales with oscillation periods that depend on nanoparticle size. This indicates very low coupling between electronic and phonon degrees of freedom. Additional work on similar systems which include various metal-centered organometallic dyes is discussed for potential applications in dye-sensitized solar cells and other optoelectronic devices.

Transient absorption studies of nanoparticles composed of optically-active molecular salts

248th National Meeting (2014)

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