Fluorescence Quenching of CdS Quantum Dots by 4‐Azetidinyl‐7‐Nitrobenz‐2‐Oxa‐1,3‐Diazole: A Mechanistic Study

Abstract

Fluorescence quenching of CdS quantum dots (QDs) by 4-azetidinyl-7-nitrobenz-2-oxa-1,3-diazole (NBD), where the two quenching partners satisfy the spectral overlap criterion necessary for Förster resonance energy transfer (FRET), is studied by steady-state and time-resolved fluorescence techniques. The fluorescence quenching of the QDs is accompanied by an enhancement of the acceptor fluorescence and a reduction of the average fluorescence lifetime of the donor. Even though these observations are suggestive of a dynamic energy transfer process, it is shown that the quenching actually proceeds through a static interaction between the quenching partners and is probably mediated by charge-transfer interactions. The bimolecular quenching rate constant estimated from the Stern-Volmer plot of the fluorescence intensities, is found to be exceptionally high and unrealistic for the dynamic quenching process. Hence, a kinetic model is employed for the estimation of actual quencher/QD ratio dependent exciton quenching rate constants of the fluorescence quenching of CdS by NBD. The present results point to the need for a deeper analysis of the experimental quenching data to avoid erroneous conclusions.

Ultrafast Transient Absorption Study of the Nature of Interaction between Oppositely Charged Photoexcited CdTe Quantum Dots and Cresyl Violet

“…In one of our earlier works, while we highlighted this important point using one specific example, we could not provide evidence of the alternate mechanism due to lack of ultrafast pump-probe facility at that time. 40 In this work, we study the interaction between water soluble mercaptopropanoic acid capped photoexcited CdTe QDs and CV, a pair chosen for satisfying excellent overlap of the emission spectrum of former with the absorption spectrum of the latter. We not only show that despite fulfilling the overlap criteria, the emission quenching of the QDs is not governed by FRET interaction of the two species, but employing femtosecond time-resolved transient absorption measurements we demonstrate that ultrafast photo-induced electron transfer from the conduction band of the QDs to CV is primarily response for the exciton quenching process.…”

“…Difference absorption spectra of the QDs (7 μM) in aqueous medium in the absence (a) and presence (b) of CV (7 μM) at various delay times(2,5,10,20,30,40,60, 70, 100 ps) after 350 nm excitation.…”

Studies on the Mechanism of Fluorescence Quenching of CdS quantum dots by 2‐Amino‐7‐Nitrofluorene and 2‐(N,N‐dimethylamino)‐7‐Nitrofluorene

“…Surface ligands depessivation can be one of the reasons for fluorescence quenching of nanocrystals . Due to depassivation of surface ligands by external influences, destruction of electron‐hole recombination state (exciton) takes place leading to quenching of fluorescence.…”

“…Recently, Santhosh et al . have shown that spectral overlap is not the sole criteria for resonance energy transfer between azetidinyl‐NBD and CdS quantum dots as in‐depth analysis over this system indicated the presence of static quenching and charge transfer between the dyad.…”

“…Fluorescence quenching of quantum dots due to resonance energy transfer and charge transfer have been studied extensively with CdSe and CdS core type quantum dots. [24, 25] However in some cases, processes like static quenching and surface charge depassivation have also been observed to be responsible for the fluorescence quenching of quantum dots . While quenching due to energy transfer is governed by spectral overlap between the donor and acceptor, quenching due to charge transfer is governed by redox potentials of donor and acceptor .…”