The Thomas lab
takes an interdisciplinary approach to the design, synthesis,
and testing of organic materials for a number of applications.
Members of the lab combine molecular and polymeric synthesis,
physical organic chemistry, materials characterization, photophysics,
lithography, and electrostatics to achieve these goals. Below are
several projects in the group:
Electrostatically-Responsive Materials: The Organic Chemistry of
Static Electricity
Materials that undergo a change in an observable property upon
exposure to a stimulus (such as light, electrical potential, a
chemical reagent, or a change in temperature) are responsive
materials. Some examples are piezoelectric materials
(response to change in volume is electrical potential) and
photochromic
materials (response to light is change in color. Our lab will
investigate a different type of material: those that respond to a
stimulus (light or a chemical reagent) by changing the sign of
charge they obtain upon contact electrification
(the process that
charges two contacting materials with opposite signs when they are
separated). Beyond empirical determination, a successful,
consistent theory that predicts the sign of charge that a material
will acquire upon contact. Recently, however, several
structure-property relationships have emerged. In this project, we
will use these structure-property relationships (and develop new
design rules) to guide the design of materials that will switch
their sign of charging. These materials will be useful in several
contexts:
- Next-generation
anti-static materials
- Chemomechanical
materials that combine sensing and actuation
- Reconfigurable
microfluidic devices
- Programmable
templates for electrostatic self-assembly
Optical Sensing
Materials: Turning the Light On with Conjugated Materials
Conjugated
materials are highly amplifying optical sensing materials because
mobile excited states can transfer their energy (or be quenched) by
electron, hole, or energy acceptors throughout the polymer
backbone. The output of nearly all sensing applications of these
materials is either fluorescence quenching or Förster Energy
Transfer, both of which have large background signal, therefore
limiting sensitivity and increasing the possibility of false
positives. Optimal sensitivity occurs when an emissive signal
appears against a dark background: existing sensing techniques with
conjugated polymers preclude this type of design. We will design
materials and films that combine amplification from mobile excitons
with dark-field sensing in several ways:
- Small
amounts of reactive quenching traps (covalently bound or dispersed
in film).
- Energy
transfer to lanthanide complexes for gated detection
- Prequenched
materials that radiate faster (e.g. by coupling to plasmons) upon
binding
Multifunctional
Polymers
Polymers can serve
as scaffolds for combining functional structural moieties that can
perform useful functions. For example, polymers that bear ligands
that bind specifically to targeted surfaces (such as cells) can
serve as inhibitors with larger binding constants than their
monomeric counterparts. Our lab will focus on multifunctional
polymers, which combine ligands for binding selectively to a surface
with other useful functions. In addition to random copolymers, we
will take advantage of recent developments in controlled
polymerization techniques to exert greater control over the
distribution and location of functional moieties. With these
materials, we will target a range of applications, including:
- Singlet
oxygen photosensitizers for photodynamic therapy
- Cationic
ammonium groups for biocidal and antibacterial applications
- Thermally
responsive materials for selective precipitation
