Fluorescence modulation of cadmium sulfide quantum dots by azobenzene photochromic switches.
We have investigated the attachment of azobenzene photochromic switches on the modified surface of cadmium sulfide (CdS) quantum dots (QDs). The modification of CdS QDs is done by varying the concentration of the capping agent (mercaptoacetic acid) and NH3in order to control the size of the QDs. The X-ray diffraction studies revealed that the crystallite size of CdS QDs ranged from 6 to 10 nm. The azobenzene photochromic derivatives bis(4-hydroxybenzene-1-azo)4,4'(1,1' diphenylmethane) (I) and 4,4'-diazenyldibenzoic acid (II) were synthesized and attached with surface-modified CdS QDs to make fluorophore-photochrome CdS-(I) and CdS-(II) dyad assemblies. Upon UV irradiation, the photochromic compounds (I) and (II) undergo a reversibletrans-cisisomerization. The photo-inducedtrans-cistransformation helps to transfer photo-excited electrons from the conduction band of the CdS QDs to the lowest unoccupied molecular orbital ofcisisomer of photochromic compounds (I) and (II). As a result, the fluorescence of CdS-(I) and CdS-(II) dyads is suppressed approximately five times compared to bare CdS QDs. The fluorescence modulation in such systems could help to design luminescent probes for bioimaging applications.
Department of Chemistry , Quaid-i-Azam University , Islamabad 45320, Pakistan.
Hina
H
Javed
Department of Chemistry , Quaid-i-Azam University , Islamabad 45320, Pakistan.
Kalsoom
K
Fatima
Department of Chemistry , Quaid-i-Azam University , Islamabad 45320, Pakistan.
Zareen
Z
Akhter
Department of Chemistry , Quaid-i-Azam University , Islamabad 45320, Pakistan.
Muhammad Arif
MA
Nadeem
Department of Chemistry , Quaid-i-Azam University , Islamabad 45320, Pakistan.
Muhammad
M
Siddiq
Department of Chemistry , Quaid-i-Azam University , Islamabad 45320, Pakistan.
Azhar
A
Iqbal
azobenzene; cadmium sulfide; fluorescence modulation; photochromic switches; quantum dots