This document summarizes research into the stability of CdSe nanoclusters in organic solvents and under different surface passivating ligands and conditions. The researchers synthesized PEG-thiolated CdSe nanoclusters and investigated their stability over 48 hours in various organic solvents and under dark/N2, dark/air, light/N2, and light/air conditions using UV-Vis spectroscopy. They found that the nanoclusters were most stable in isopropanol and under dark/N2 conditions, and that ligands with longer PEG chains provided better stability. Future work will explore synthesizing and studying the stability of other metal chalcogenide nanoclusters.

1. 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 nanoclusters
Successfully 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/air
Use 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