Photophysical studies of CdTe quantum dots in the presence of a zinc cationic porphyrin

The photophysical properties of 2.3 nm thioglycolic acid (TGA) coated CdTe quantum dots (QDs) prepared by a reflux method have been studied in the presence of cationic meso-tetrakis(4-N-methylpyridyl) zinc porphyrin (ZnTMPyP4). Addition of the CdTe QDs to the porphyrin in H2O
results in a marked red-shift and hypochromism in the porphyrin
absorption spectrum, indicative of a non-covalent binding interaction
with the QD surface. Only low equivalents of the quantum dot were
required for complete quenching of the porphyrin fluorescence revealing
that one quantum dot may quench more than one porphyrin. Similarly
addition of porphyrin to the quantum dot provided evidence for very
efficient quenching of the CdTe photoluminescence, suggesting the
formation of CdTe'porphyrin aggregates. Definitive evidence for such
aggregates was gathered using small angle X-ray spectroscopy (SAXS).
Ultrafast transient absorption data are consistent with very rapid
photoinduced electron transfer (1.3 ps) and the resultant formation of a
long-lived porphyrin species.