Fluorescence modulation of CdTe nanowire by azobenzene photochromic switches

Abstract

Photoinduced electron transfer (ET) and Forster Resonance Energy Transfer (FRET) between azobenzene derivatives (Quencher) and CdTe nanowires have been investigated. Needle-like cadmium telluride (CdTe) 1D nanowires were successfully prepared. The surface modification was done by the capping agent 3-marcaptopropanoic acid (MPA) and NH3. The azobenzene derivatives (E)-5-((4-chlorophenyl) diazenyl)-2-hydroxybenzaldehyde Q(I) and (E)-4-((3-formyl-4-hydroxyphenyl) diazenyl) benzene sulfonic acid Q(II) have been prepared and glued to MPA capped CdTe nanowires. After UV treatment, the azo compounds Q(I) and Q(II) experience a reversible trans–cis isomerization. The photoinduced trans to cis change supports the transfer of electrons from the conduction band (CB) of the CdTe nanowires to the lowest unoccupied molecular orbital (LUMO) of cis isomer of the azo compounds and the overlapping absorbance spectra of acceptor (QI & QII) with the emission spectrum of donor (CdTe nanowires) also suggests quenching of PL due to Forster energy transfer (FRET). Using steady state (SSPL) and time resolved fluorescence (TRPL) measurements, we have noticed that with the increase in Quencher (I) & (II) concentrations, the fluorescence is quenched with a subsequent decrease in decay life time. Hence fluorescence can be modulated at different quencher concentrations.