A Study of the Binding of Cyanine Dyes to Colloidal Quantum Dots Using Spectral Signatures of Dye Aggregation

Abstract

This paper describes the use of the spectral signatures of near-infrared (NIR) absorbing cyanine dyes to quantitatively analyze their intermolecular interactions upon adsorption to colloidal CdSe quantum dots (QDs) with diameters of 2−3 nm. Spectroscopic characterization of the disaggregation of two types of sulfonate-functionalized cyanine molecules, IR783 and IR820, from H-aggregate dimers to monomers upon addition of methanol yields spectral signatures of aggregation used to analyze the response of the dyes to exposure to CdSe QDs. The spectrally distinct absorbances of the cyanines and QDs enable a factor analysis procedure that decomposes the absorbance spectrum of the QD/ cyanine mixture into three distinct componentssolution-phase cyanine molecules (in monomer and H-aggregate form), QDbound cyanine monomers, and disordered, QD-bound cyanine aggregatesas a function of the molar ratio of cyanine to QD. The presence of these three distinct components strongly suggests that cyanines initially bind to QDs as either disordered aggregates (for small molar ratios of QD:cyanine) or as monomers (for large molar ratios of QD:cyanine). Quantitative analysis of the adsorption motifs of cyanine dyes on nanocrystalline semiconductors is a first step in understanding the influence of binding geometry on the rate and mechanism of charge transfer across the organic−inorganic interface within cyanine-sensitized photoconversion materials.

Fluorescent J-aggregates of cyanine dyes: basic research and applications review

“…Nanotubular J-aggregates can be very efficient in this respect [218]. It was reported, however, that the strong heterogeneity may appear on their binding to QDs, which involves free and bound monomers in addition to J-aggregates [169]. Because of weak binding, such distribution between bound J-aggregates and free monomers can be concentration-dependent [156].…”

The influence of phthalocyanine aggregation in complexes with CdSe/ZnS quantum dots on the photophysical properties of the complexes

“…It is well-known that the aggregation of acceptor molecules can dramatically reduce the functionality of the complexes [19]. To our knowledge, there are only a few papers [28–29] devoted to the investigation of how the spatial arrangement of acceptor molecules –in complexes of QD donors with several acceptors– influences the photophysical properties of the complexes. Therefore, this problem important for PDT application needs to be clarified.…”

Density functional investigation and some optical experiments on dye-sensitized quantum dots

“…We note that charge transfer from the dye to the QD (or vice versa), depends on the QD material, size, interaction with the QD surface etc. 17,28,31,34 .…”