A solvent sensitive coumarin derivative coupled with gold nanoparticles as selective fluorescent sensor for Pb2+ ions
Mehebub Ali Khan1, Surendra Meena2, Md Akhtarul Alam1
1Department of Chemistry, Aliah University, IIA/27, Action Area II, Newtown, Kolkata 700 160, India.
Abstract:
A coumarin based fluorescent molecule, 3-amino-2-cynano-3-(7-diethylamino-2-oxo-2H-chromen-3-yl)-acrylic acid ethyl ester (1) has been synthesized and characterised. Photophysical studies of 1 exhibit polarity dependent shift of its emission maxima which have been explained on the basis the existence of polar excited state of the molecule. Combination of compound 1 and citrate capped AuNPs (AuNPs/1 conjugate) has been used as a sensing tool for heavy metals. AuNPs/1 conjugate has been found to detect Pb2+ selectively by naked-eye color change as well as fluorescence enhancement. On addition of molecule 1 to gold nanoparticles solution, the color of the solution becomes reddish followed by quenching in fluorescence intensity. With gradual addition of Pb2+, the solution of AuNPs/1 conjugate becomes violet accompanied by a fluorescence enhancement. Excited state lifetime measurement revealed that compound 1 exhibits very fast decay pattern in aqueous medium whereas in AuNPs medium the lifetime of 1 increases. Upon addition of Pb2+ ions to that AuNPs/1 solution the lifetime of 1 decreases again. Based on the experimental observations the mechanism of sensing of lead has been proposed thoroughly. Initially compound 1 gets absorbed on the surface of the spherical gold nanoparticles. When Pb2+ is added, probably gold nanoparticles aggregates to form bigger particles by releasing compound 1 from its surface to show fluorescence enhancement.
