Tuning of chalcogenide nanoparticles fluorescence by Schiff bases
Graphical abstract
The interactions among chalcogenide colloids and Schiff bases in the presence and absence of an electron withdrawing group (nitro group) in organic media was studied using fluorescence and fluorescence life time studies.
Highlights
► The chalcogenide nanoparticles (CN) have been synthesized using microwave technique. ► Lifetime measurements suggest the presence of dynamic quenching processes. ► Schiff base (SB) with a nitro substituent acts as an efficient quencher. ► Quenching efficiency of SB gives a way to control the luminescence properties of CN.
Introduction
Studies on chalcogenide nanoparticles have been at the focus of intense research due to their unique size-dependent physicochemical and optoelectronic properties [1]. This size quantization effect allows chemists and material scientists, a distinct opportunity to modify their surface properties in addition to their electronic and chemical properties simply by controlling the particle size [2]. The electronic properties of nanoparticles can be studied by monitoring their luminescence properties in the presence of electron or hole acceptors [3], [4].
Chalcogenide semiconductor nanoparticles, such as CdS and CdSe, have been extensively studied due to their potential applications in various fields such as solar cells, field effect transistors, light emitting diodes, photocatalysis, biological fluorescent labels and biological sensors [5], [6], [7]. Among the various methods available to synthesize chalcogenide nanoparticles [8], [9], [10], [11], [12], microwave technique has attracted significant attention due to the dramatic enhancement in reaction yields, reduction in reaction time, ease of purification, use of less solvent and greater flexibility in reaction conditions [13], [14], [15].
Recently, many groups [3], [4], [16], [17], [18] studied the interactions of chalcogenide nanoparticles with different substrates using steady-state and dynamic fluorescence spectroscopy, which are the main constructive tools in monitoring the electronic properties of nanoparticles.
In this work, we have studied the interactions of chalcogenide nanoparticles (CdS and CdSe) with Schiff bases in the presence and absence of an electron withdrawing group. Schiff bases, which are derived from the condensation of primary amines and aldehydes or ketones and characterized by the anil linkage HCN, possess structural similarities with natural biological substances. They have a wide variety of applications in biological, inorganic, clinical and analytical fields [19], [20]. They are known to exhibit potent antimicrobial (antibactericidal, antiviral and antifungal), anticonvulsant, anti-inflammatory and insecticidal activities [19], [20], [21]. In addition some Schiff bases show pharmacologically useful activities like anticancer (radical scavenging activity), anti-hypertensive, antifertility, analgesic, anthelmintic, and hypnotic activities [21].
Section snippets
Materials
Cadmium chloride, sodium sulfide, sodium selenite, hydrazine, salicylaldehyde, 4-nitroaniline and aniline were of analytical grade purchased from Aldrich chemicals and used as received. All solvents used were of extra pure analytical grade.
Microwave assisted synthesis of CdS nanoparticles
CdS nanoparticles were synthesized using the method by Yang et al. [22] 0.05 M Na2S, dissolved in distilled water (25 ml), was added drop-wise to a 100 ml round bottom flask containing 25 ml of 0.05 M aqueous solution of CdCl2. The mixture was stirred using
Characterization of CdS and CdSe nanoparticles
Fig. 1a shows the absorption spectra of microwave synthesized CdS and CdSe nanoparticles dissolved in DMF. They show absorption onsets at 480 nm (2.58 eV) for CdS and 556 nm (2.23 eV) for CdSe, whereas bulk CdS and CdSe particles show absorption onsets at 512 nm (2.42 eV) and 716 nm (1.73 eV), respectively. The apparent blue shift in the absorption onsets for both CdS and CdSe can be attributed to the quantum-size confinement effect [1], [2]. From the absorption onset, the mean grain size of
Conclusions
Platelet-like CdS and CdSe nanoparticles with average size of ∼5–10 nm and ∼8–12 nm were synthesized using a simple microwave technique. The interactions among chalcogenide nanoparticles and Schiff bases with and without electron withdrawing group were investigated using fluorescence studies. The results showed that Schiff base with a nitro substituent (N-salicylidene-4-nitroaniline) is an efficient quencher. Schiff bases might interact with the chalcogenide nanoparticles initiated through ground
Acknowledgements
Author SA and MA thanks DST, New Delhi (INT/AUS/P-1/07 dated 19th Sep 2007) and DEST, Australia for the sanction of INDIA-AUSTRALIAN strategic research fund for their collaborative research. Author SA thank DST, New Delhi (SR/S1/PC-49/2009) for major research project. Authors SA and SV thank DST for sanctioning FIST (SR/FST/CSI-190/2008 dated 16th March 2009) and Nanomission (SR/NM/NS-27/2008, dated 25th Feb 2009) projects. Also the authors thank Prof. P. Ramamurthy, Director, National Centre
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