Influence of Organic Solvents and Surface Passivating Ligands on the Stability of CdSe Nanoclusters

Charles D. Irving, Katie N. Lawrence, Sukanta Dolai, Meghan B. Teunis, and Rajesh Sardar*

Department of Chemistry & Chemical Biology, Indiana University Purdue University Indianapolis, Indianapolis, IN 46202, United States.

Synthesize PEG-thiolated monolayer protected nanoclustersSuccessfully transfer nanoclusters to an organic layer Determine post-synthetic stability of nanoclusters in

organic solvents. Investigate the influence of surface passivating ligands on

the stability of nanoclusters.Study the stability of nanoclusters over 48 h using common bench top storage techniques: dark/N2,dark/air, light/N2, light/airUse UV-Vis Spectroscopy, to determine if the integrity of the core is withheld.

Temperature and pH parameters were found to influence the growth and stability of our nanoclusters..

Our nanoclusters possessed unique solubility properties which allowed them to be reimmeresed in a variety of solvents.

The PEG18 chain length was found to have a stronger diffusion barrier than PEG6 thus producing more stable nanoclusters.

Photooxidation was found to be the most detrimental environment thus dark/N2 was found to be ideal.

The SNCs showed the longest stability in an isopropanol medium.

This work was supported by the Start-up Funds provided by IUPUI.

Stability is the key for long term use of CdSe nanoclusters (NCs) in many applications. For example, photovoltaic devices, which commonly use CdSe NCs suffer from insufficient efficiency due to the decomposition of NCs in an aqueous medium. Currently, Na2S is the most commonly used electrolyte, which captures the photo-generated holes and increases the stability. However, Na2S increases the solution pH ~13 during the photocurrent measurement and at this pH, CdSe NCs undergo decomposition. Therefore, a system should be developed where photocurrent measurement can be done in organic solvent/electrolyte medium using an organic hole scavenger. Recently we have developed a synthesis of PEG-thiolate protected CdSe NCs with unique solubility properties that allow the NCs to dissolve in a variety of solvents such as acetonitrile, ethanol, methanol, and dichloromethane. We believe that these newly synthesized CdSe NCs show promise for the use in photovoltaic devices to increase the efficiency since organic solvents could be substituted for the aqueous medium currently used. However, in order to design efficient photovoltaic devices with enhance stability, it is important to study the stability of these NCs in a variety of organic solvents and compare these results with the NC’s stability in an aqueous medium. Herein we present an investigation of the influence of organic solvents and thickness of the surface passivating ligands on the stability of CdSe NCs. We have used alcohol, chlorinated, and coordinating solvents due to their diverse polarity and electrolyte ion mobility. Time dependent stability of these CdSe NCs was monitored over 48 h under benchtop conditions such as light/air, light/N2, dark/air, and dark/N2.

Future studies will be performed on the synthesis of PEG-S- stabilized various metal chalcogenide nanoclusters, which include CdS, CdTe, ZnS, ZnSe, CuS, CuSe, AgSe, AgS, and CdSe/ZnS. Purification of these nanoclusters as well as their solution phase electrochemical properties will be investigated. An in depth look at their stability in both aqueous and organic mediums will also occur. These studies are in their preliminary stages.

Abstract

Research Objectives

Photophysical Stability Properties

pH/Temperature Study

Conclusion

Future Research

Acknowledgment

H2O CH3CNH2O* CHCl3 DCM THF C2H5OH PhCN

Synthesis of PEG-Thiolate Monolayer Protected CdSe Nanoclusters