Entering graduate studies, I had a clear vision: renewable, tunable, biodegradable
organic electronics. Renewable technologies and luxuries enjoyed by society might
prevent catastrophe due to energy shortage as demand increases. With this vision in mind,
my focus was to work towards applications of organic electronics. Specifically, work
towards the goal of biodegradable, tunable, renewable organic electronics was focused on
heterogeneous systems. Scientists and engineers most often work with composites,
mixtures, and amorphous materials and Nature has produced optimized structures that are
heterogeneous. Recognizing this and knowing that energy is the world’s primary concern
motivated the study of electronic processes in heterogeneous systems.
Being a physical chemist with a background in automotive repair meant having an
interest in both fundamental science and its applications. I believed that the farthest reaches
of computation could meet the farthest reaches of experiment on challenging but applicable
systems. Applicable implies commercially and industrially viable systems. This also
implies ease of processing which is often associated with an increase in heterogeneity.
Ideally, measuring charge transfer in heterogeneous organic electronics on a mechanical
level would enable their rational design. Mechanical here refers to ultrafast time scales or
molecular scales. For example, the measurement of the rate of individual charges hopping
would be the mechanical level as opposed to a thermodynamic bulk level measurement
like charge mobility or conductivity.
Researching the connection between mechanical properties like ultrafast
vibrational dynamics or molecular charge hopping and then correlating thermodynamic
bulk properties of heat capacity, charge mobility, or conductivity is still an enticing
challenge. Bulk properties that have been historically observed are catalysis reaction rates,
charge mobility, large-scale morphological changes like glass transition or annealing,
coefficient of thermal expansion, etc. Their mechanical corollaries would be molecules
reaching transition states, charge hopping between molecular sites or distinct subensembles
as opposed to bulk mobility, or ultrafast changes in vibrational correlation as these
processes occur. Catalysis is an example of why this might be of interest. For a rate of
catalysis with a given concentration, one could have 100% of the catalytic species
facilitating 10 times the uncatalyzed reaction rate. Alternatively, one could have 1% of the
catalytic species facilitating 1000 times the uncatalyzed reaction rate. Both scenarios
would appear the same on the thermodynamic level but would differ on the mechanical
level. Rational design of chemical systems begins at the mechanical level, but the effects
of interest are often observed on the bulk scale.
This connection between the quantum mechanical and the thermodynamic is an
open area of research both theoretically and experimentally. These connections are almost
completely obfuscated for disordered systems and in many respects are only approachable
with phenomenological analysis. Affirming or negating hypotheses that specific
vibrational dynamics unique to each molecular configuration give rise to protein function,
catalytic mechanisms, or are the source of the apparent charge mobility ceiling in organic
electronics (OEs) would change the direction of a tremendous amount of research effort.
To illustrate with another example, if it were known that charge mobility were limited byvi
charge hopping rates, and charge hopping was limited by molecular motions modulating
wavefunction overlap, then the applications of OEs would be limited. If this were known,
it would prevent wasted effort on applications that were practiallly beyond reach.
Similarly, if a catalytic species had only a small population of extremely active conformers
it would be necessary to know this in order to improve their function in an efficient rational
Given the challenges in applying theory to heterogeneous systems, comparative
experiments are one way to connect 2D-IR data to physical processes on both the
thermodynamic and mechanical level. This approach involves changing one variable
within the molecule or system, observing changes in spectra, and then connecting these to
system properties to enable rational design of systems or their moieties. The ultrafast time
scales of 2D-IR and its multidimensional nature allow one to decompose ensembles within
heterogeneous systems experimentally. Then the efficient application of theory to a subset
of a system is approachable. This is opposed to the currently intractable task of modeling
an entire heterogeneous system and all its properties at once. Ultrafast 2D-IR is a technique
capable of decomposing ensemble measurements and monitoring their dynamics on
femtosecond time scales. The capabilities of this technique are manifest in the results
below: measurement of temperature dependent intramolecular proton exchange rates, gas
adsorption and exchange within heterogeneous systems, solvent effects on complex
formation, and morphological changes in the surfaces of nanoparticles
University of Minnesota Ph.D. dissertation. 2020. Major: Chemistry. Advisor: Aaron Massari. 1 computer file (PDF); 181 pages.
Two-Dimensional Infrared Spectroscopy of Heterogeneous Systems: On the Path to Measuring Charge Transfer in Solution Processed Organic Electronic Thin Films.
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