Abstract
Dye molecule 3SAH, gold nanoparticle (GNP), and 3SAH-GNP were measured by sub-picosecond transient absorption spectroscopy. The aggregation of 3SAH exists with concentrations larger than 1×10-6 M, and shows long emission lifetime due to more rigid structure. For 5 nm GNP, time constants of electron-phonon and phonon-phonon are obtained to be 2.3 and 140 ps, respectively in fitting to a two-temperature model. The dephasing time less than 60 fs indicates an ultrafast electron scattering. For 3SAH-GNP, the absorption of 3SAH+ arises less than 200 fs indicating the electron injection from excited 3SAH to GNP with high efficiency. The process of back electron transfer from GNP to 3SAH competes well with electron-phonon interaction in GNP, and becomes dominant under condition of large ratio of surface to volume in GNP. The participation of back electron transfer plays a second pathway for heat dissipation in GNP. Trinucleus metal complexes, Ni3(dpa)4(NCS)2, Ni3(dpa)4Cl2, Co3(dpa)4(NCS)2,and Cr3(dpa)4Cl2 are studied by transient absorption spectroscopy. Their ligand-center π-π* and charge transfer states are accessed via laser excitation then quickly transfer to ligand-field states at time constants 0.2-0.4 (Ni3), <0.1 (Co3), and <0.1 ps (Cr3), respectively. Time constants obtained for ligand-field states back to ground state are related to the spin-orbit coupling constants (Ni3 > Co3 > Cr3) and the energy gap between lowest-lying excited state and ground state (Cr3 > Co3 ≈ Ni3). They are obtained to be 3 (Ni3), 15 (Co3), and 200 ps (Cr3).