Fluorescence dynamics of zinc protoporphyrin in solution and inside anodized aluminum oxide (AAO) nano-channel arrays

Abstract

The excited-state relaxation dynamics of zinc protoporphyrin (ZnPP) in THF solution and inside nano-channel arrays of anodized aluminum oxide (AAO) have been investigated with time-correlated single-photon-counting (TCSPC) fluorescence spectra with S-2 excitation (lambda(ex) = 435 nm). We used three initial concentrations of immersion - 4.8 x 10(-6), 4.8 x 10(-5) and 4.8 x 10(-4) M - to examine the extent of aggregation of ZnPP inside the AAO nano-channel arrays of two pore sizes - 15 and 70 nm. Only one decay component corresponds to the aggregation of ZnPP in THF solution, whereas at least two decay components are required to describe the transient behavior of ZnPP inside AAO. The observed systematic variation of the decay coefficients and the corresponding amplitudes of the ZnPP/AAO samples are consistent with the observation of steady-state spectra of the system reported previously (JCCS 2006, 53, 201), but through fluorescence lifetime measurements we further highlight the significance of aggregation of ZnPP in the specific nanoporous environment that is not achievable in ZnPP/THF solutions in large concentrations.