Interaction between TPPS4 porphyrin and CdTe-3-MPA quantum dot: Proton and energy transfer

Abstract

Interaction between meso-tetrakis(p-sulfonato-phenyl)porphyrin (TPPS4) and cadmium telluride QD functionalized by 3-Mercaptopropionic Acid (CdTe-3-MPA QD) in water solution was investigated using the optical absorption and fluorescence spectroscopies. TPPS4 and QD spectral and temporal characteristics were studied separately and at their interaction at pH 4.0, where TPPS4 possesses charge 2- and QD are neutral, and at pH 7.0, where TPPS4 charge is 4- and QD are negatively charged. The analysis of quenching of the TPPS4 fluorescence by QD and QD luminescence by TPPS4 shows that the interaction reduces the intensities and lifetimes of the porphyrin fluorescence and QD luminescence. The interaction of TPPS4 with QD at pH 4.0 occurs via two mechanisms: proton transfer from the porphyrin to QD and the energy transfer from QD to porphyrin, while at pH 7.0 just energy transfer takes place. The CdTe-3-MPA QD luminescence has two components, which differ by their spectral position and lifetimes. These components are associated with the electron-hole annihilation in the QD CdTe core and in 3-MPA functionalization layer. Higher value of the accessibility factor at pH 4.0 (f1 = 0.95 ± 0.06) than that at pH 7.0 (f3 = 0.37 ± 0.03) shows that electrostatic interaction is important at the TPPS4 – QD interaction.