Surface Properties, Interface Events and Energy Relaxation Processes in Nanoassemblies Based on Ag-In-S/ZnS Quantum Dots and Porphyrins

Abstract

Based on comparative experimental spectral-kinetic data and quantum chemical calculations (method MM+) it was argued that in water at pH 7.5 and ambient temperature, electrostatic interactions of positively charged 5,10,15,20-tetra(N-methyl-4-pyridyl)porphyrin molecules (free bases) with negatively charged glutathione stabilized core/shell semiconductor quantum dots (QD) AIS/ZnS/GSH lead to the formation of stable «QD-porphyrin» nanoassemblies. The obtained results indicate that interaction of AIS/ZnS/GSH QDs with positively charged H2P4+ molecules is not described appropriately by the Poisson statistics (the nanoassembly stoichiometry is 1:1), and followed by a very fast metalation of porphyrin free base (formation of the extra-ligated Zn-porphyrin complex) which is directly fixed on the QD surface. The detailed analysis of experimental results and structural parameters for the size-consistent 3D model of the above «QD-porphyrin» nanoassembly evidently showed for the first time that the non-radiative relaxation of QD excitonic excitation energy is due to competitive processes: FRET QD ® porphyrin and the electron tunneling through the ZnS barrier to the outer interface of the QD in conditions of quantum confinement.