Fluorescence Switching of Quantum Dot in Quantum Dot-Porphyrin-Cucurbit [7] Uril Assemblies

The fluorescence switching of alloy (Cd1-xZnxS) quantum dot (QD) in the presence of porphyrin and cucurbit [7] uril has been demonstrated using steady-state and time-resolved spectroscopy. The assemblies of Cd1-xZnxS QD, 5-(4-aminophenyl)- 10,15,20-triphenyl-21H,23H-porphyrin (APTPP), have been prepared by electrostatically attaching the negatively charged QD with positively charged APTPP. The drastic photoluminescence (PL) quenching and the shortening of decay time of alloy QD in the presence of porphyrin indicate the efficient energy transfer from QD to porphyrin. It is interesting to note that the PL quenching varies with changing the alloy composition, which reveals that the quenching of QD luminescence by porphyrin could be used as a probe for detection of porphyrin. Furthermore, in the presence of cucurbit [7] uril, CB[7] acts as a receptor to bind the porphyrin (quencher) and restore the luminescence of the QD by preventing the energy transfer from QD to porphyrin. Encapsulation of APTPP molecules within CB[7] is confirmed by steady-state and time-resolved anisotropic spectroscopy. The turn off/on fluorescence of luminescent QD opens a new opportunity for designing a new optical-based sensor for bioapplications.