Our group explores charge and energy transfer dynamics in
with potential utilization in solar energy conversion and biosensing. Most of
our studies are based on time-resolved single particle methods. We
organic/inorganic nanomaterials, biological/inorganic nanostructures and
conjugated polymers. We use self-assembly methods to connect various
nanomaterials to obtain hybrids controlled
optical behavior. Various single particle methods are available in our
group and described in the Instrumentation page.
They can be accessed
through the CFN user program. Some of our recent work is briefly described
1. Hybrid Nanomaterials
for Solar Energy Conversion
Charge transfer and energy transfer are among the most important
processes occurring in hybrid solar cells. Nanoscale
characterization and control of such processes is an important research topic in our group.We use self-assembly methods to create quantum dot-based hybrid nanomaterials
with controlled behavior, in particular charge transfer, energy transfer and plasmon-assisted
emission. Through self-assembly we regulate molecular parameters
such as intercomponent distance, bandgap or metal nanoparticle size
to control the magnitude and fluctuation of various light-induced processes .
Some examples highlighting recent results are shown below.
- Qdot-bridge-fullerene hybrids with controlled ET
We developed a surface-based self-assembly method to produce donor-bridge-acceptor
with varying bridge length and varying Qdot core size (bandgap) that exhibit
transfer (ET) rate. With excellent, size-dependent light absorption properties
conferred by the incorporated Qdots, these dimeric hybrids are promising power generating nanounits for molecular electronics.
related articles in Angew.Chem.Intl.Ed.2011 and in
- Qdot/Conjugated Polymer hybrids with controlled HT
In collaboration with Maye's group at Syracuse, we produced a series of Qdot/conjugated polymer hybrids
with tunable hole transfer rate by using
core/shell Qdots with varying shell thickness and connecting the components by
electrostatic binding. (see
related article in ACS Nano).
In collaboration with Oleg Gang (BNL), we demonstrated control of
photoluminescence in plasmonic Qdot heterodimers composed of Qdots linked with
gold nanoparticles by DNA. Heterodimers with properly engineered interparticle
distances were found to exhibit photoluminescence enhancement as
large as 20x compared to a single Qdots when optically pumped at surface plasmon
related article in ChemComm 2010).
2. Hybrid Nanomaterials for Biosensing
We have been active in developing Qdot/protein hybrids for biosensing.
In a collaboration with Basil Swanson's group at LANL, we reported in
Small 2009 a Qdot/protein hybrid using a genetically engineered
chaperonin, the first reported Qdot/protein with controlled (1:1) stoichiometry
and with multiple binding sites allowing detection of target molecules with high
3. Structure-Function Relationship in
Conjugated polymers are cost-effective materials with high promise in
photovoltaic, light emitting diode and biosensing. The electronic and optical properties of
these materials strongly dependent on the polymer chain conformation and
aggregation state. Understanding structure/optical properties relationship in
such materials and developing synthetic or materials processing ways to control
the structure towards imroved performance is an area where we have been active
in collaboration with Hsing Lin Wang's group at LANL (polymer synthesis).
2011 we reported a method to fabricate conjugate
polymer based microporous thin films with high transparency and efficient
charge transfer with potential utilization as active substrates for transparent
PVs. These thin film show structural regularity over large areas consist of
hexagons with sizes 3-5μm, with most polymer material concentrated in the
hexagonal frame. Recently we have been successful in applying the method
to commercial conjugated polymers and to scale it up to sizes relevant to PV
- Water soluble nonionic conjugated polymers are explored in
organic light emitting diodes due to their environmental friendly processing. In
2010, we showed that polymer/solvent interactions can be employed
to control the polymer chain conformation in the case of a non-ionic conjugated
polymer. Depending on the polarity of the solvent, we found the polymer to
exhibit extended, coiled, and collapsed chain conformations in solutions, which
lead to distinct morphology and optical properties in solid films.
Applied Materials and Interfaces 2011 we reported a series of
water-soluble conjugated polymers with varying side chain length (
repeat units) with
side-chain-dependent conformation and solvent-dependent photoluminescence
properties. we found that an increase in EG repeat units induces changes in chain packing,
and affects crystallinity which evolves from semicrystalline to liquid
crystalline to completely amorphous.
we reported a temperature-dependent time resolved study that help us untangle
the role of polymer chain conformation and aggregation state in defining the
thermochromic properties of a PPV derivative.
- In a more recent collaboration with Wang's group, we
developed a label free DNA sensor with sequence specificity and based on a water
soluble cationic PPV and cationic intercalators and demonstrated sequence
specific optical behavior of a conjugated polymer.