LAUSR

Abstract A series of stable CuO quantum dots (QDs) in aqueous alkaline medium are prepared and protected against rapid oxidation by capping with mercaptoacetic acid (MAA). The MAA not only regulates the size of the CuO QDs but it also acts as pendent group for further functionalization of QDs. A specific concentration of MAA improves the crystallinity and increases the fluorescence lifetime by decreasing the density of surface trap states. The MAA capped CuO QDs are attached to (E)-5-((4-chlorophenyl) diazenyl)-2-hydroxybenzaldehyde (CPDHB) and upon UV irradiation at 300 nm the CPDHB experiences a reversible trans- to cis-isomerization. The absorption band of the cis-isomer of CPDHB overlaps with the fluorescing band of the CuO QDs, as a result the fluorescence of the QDs is strongly quenched. The photoluminescenc (PL) quenching is attributed due to the photoinjected electron transfer from the conduction band (CB) of the CuO QDs to the lowest unoccupied molecular orbital (LUMO) of the cis-isomer of CPDHB. Forster resonance energy transfer (FRET) is also observed but its contribution is minor. The fluorescence quenching of CuO QDs in QDs - CPDHB assembly upon ultra-violet excitation and reversible trans-cis interconversion of CPDHB may potentially suggests to design fluorescent probes for bioimaging and to develop data and energy storage devices.