Human skin oils are significant scavengers of atmospheric oxidants in occupied indoor environments. Many techniques used to study gas-phase transformations of surface films indoors have been limited to off-line bulk analysis, although more surface-selective methodologies are emerging. Here, we present a multi-prong analytical approach to characterizing skin oil ozonolysis. Skin...
The unique ability of plasmonic nanoparticles to localize and enhance resonant electromagnetic fields has enabled a wealth of discoveries from enhanced spectroscopies to driving chemical reactions on the nanoscale. In this thesis, we strive to both drive and observe chemistry on plasmonic surfaces. First, we examine the possibility of driving...
The three dimensional structure of a protein determines its biological function. How a protein folds, however, has been the central research problem for decades. The intermediates on the folding paths, which the protein can assume transiently, are of particular interest as they not only reveal the structural dynamics of a...
Biogenic secondary organic aerosol (SOA) particles, produced by forest ecosystems across the globe, are principal, yet poorly understood constituents in the climate system. These atmospheric particles form when biogenic volatile organic compounds (BVOCs) react with atmospheric oxidants, leading to increasingly lower volatility oxidation products that partition into the condensed phase...
This thesis document is comprised of three research projects. The first investigates the active vibrational modes involved in twisted intramolecular charge transfer in a Julolidine-BODIPY dyad using two-dimensional electronic spectroscopy along with DFT calculations. We identified two types of vibrations, compression and torsional motion, as playing an important role in...
In solar energy conversion ranging from artificial photosynthesis to photocatalysis, transition metal complexes (TMC) are essential building blocks due to several attractive properties: intense absorption within the solar spectrum, presence of charge-transfer excited state, and substrate binding capability through coordination geometry changes. In order to gain insight into controlling solar...
Organic semiconductors have shown great promise for optoelectronic applications, particularly solar photovoltaics. Critical to their success is the ability to understand and manipulate the relationship between molecular structure and bulk properties. Substantial progress on understanding structural influences on electronic properties has been made for the conjugated polymers and small molecules...
Electrochemical reactions on the nanoscale play a pivotal role in a variety of areas, including electrocatalysis, energy conversion and storage, corrosion prevention, plasmon driven chemistry, and so forth. An in-depth knowledge of how site-specific compositions and morphologies locally affect the electron transfer kinetics will greatly benefit the design of catalysts,...
This dissertation explores ways to utilize physical parameters at the nanoscale interface to control the properties of mixed-dimensional heterojunctions (MDHJs). MDHJs combine the desirable properties of different classes of low-dimensional nanomaterials (materials that are quantum confined in at least one dimension). While MDHJs have achieved superlative performance for a variety...
Many processes in nature and human-made settings rely on the unique properties of charged metal oxide:aqueous interfaces. Despite their ubiquity, these buried interfaces are challenging to study, since any analytical technique aiming to overcome the relatively small number density of interfacial versus bulk species must be highly sensitive and surface-selective....
This dissertation focuses on the study of the superionic state in multicomponent systems, where the smaller component exhibits delocalization and mobility while still maintaining system compactness through component attractions. Superionic behavior is widely observed in various systems and plays a crucial role in ceramic superionic conductors, which offer high ion...
Spin-orbit coupling (SOC) underlies myriad phenomena in chemistry and physics. Arbitrary manipulation of spin-orbit coupling would enable precise control over such parameters as magnetic anisotropy, the sensitivity of quantum sensors, and even the selectivity of certain catalytic processes. Herein, I describe my efforts directed towards utilizing SOC as a handle...
Numerous photophysical processes in both natural and artificial systems are dictated by the interaction between chromophores. For example, in photosynthesis, light is absorbed by an antenna complex composed of an array of chlorophyll chromophores that collectively transfer the energy to the reaction center where interactions between a series of redox...
Increasing industrialization and the resulting negative environmental impacts highlight the need to develop alternative renewable energy sources. The Sun is a massive source and organic solar cells are a growing field of study. As new materials are synthesized, the efficiencies of organic solar cells continue to grow, but without an...
Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical technique that can detect single molecules and simultaneously obtain structural information. When an analyte molecule binds to a nanostructured noble metal surface, the otherwise weak normal Raman signal is enhanced by as much as a factor of 108. This makes SERS the...
The development and use of organic anionic chromophores that absorb the entire visible spectrum & into the near-infrared region while providing highly reducing equivalents is pinnacle for artificial photosynthesis. This dissertation investigates the rational design of new donor-acceptor systems for artificial photosynthesis that couple naphthalene diimide (NDI)/perylene diimide (PDI) radical...
Metal halide perovskites have recently emerged as one of the most promising active layers in solar cells for their high power conversion efficiency (>25%) and ease of synthesis and deposition. Spatial heterogeneity is inevitable with current fabrication methods for both monocrystalline and polycrystalline perovskite thin films and crystals. The morphology-dependent...
This dissertation describes the study of photoinduced charge transfer between QDs and molecular acceptors as a probe of the defects within ligand shells of QDs and as means to photocatalyze redox reactions. For charge transfer reactions to occur between QDs and molecules in bulk solution, the molecules must interact with...
Plasmonic nanoparticles have very large absorption cross sections and can concentrate the local density of photon states on the nano scale. When they are coupled to molecules or semiconductor nanocrystals and form different hybrid nanostructures, various light-matter interaction processes can be significantly enhanced or manipulated, including optical responses like fluorescence...
Quantum mechanical phenomena are playing tremendous roles in many areas of chemistry and materials science research. In recent years, the potential role of coupling between electronic and vibrational degrees of freedom in photochemical processes has been widely researched. Despite its potential to improve molecular technologies, the lack of studies focusing...
Organic photovoltaics offer an opportunity to make solar cells more affordable and widely accessible using cheap, solution-processable light-absorbing layers. In order to realize new technologies, a fundamental understanding of organic chromophore photophysics is required to overcome efficiency limitations. Throughout this doctoral work, I investigated the kinetic and physical characteristics of...
Creating sustainable and clean sources of energy is an outstanding problem of importance for the current generation of scientists to solve. Organic photovoltaics (OPVs) are a promising renewable energy source but require improvements to their architectures and better fundamental understanding of the effects of organic chromophore morphology on the resulting...
Over the past 15 years, there have been significant developments in expanding the singlet fission (SF) library and understanding the SF mechanism. SF has been a topic of interest in recent years due to its potential applications in organic photovoltaics. During SF, a singlet exciton energetically down-converts into two triplet...
In this Thesis, I describe some recent developments in the field of artificial molecular machines to which I have made contributions. In Chapter 1, I survey the rise and promise of molecular nanotopology, a relatively new discipline focusing on molecular knots and links that offers unprecedented opportunities to access high-energy...
This work examines important heterogeneous processes of organic molecules on surfaces, in the contexts of atmospheric and indoor environments. In large forest ecosystems, biogenic secondary organic aerosols (SOAs) constitute a dominant fraction of organic particulate matter in the atmosphere. The formation of SOAs starts from the emission of volatile organic...
Thermoelectric devices utilize semiconducting n-type and p-type thermoelectric materials to convert heat into electricity. Despite their promise for deep space power generation or waste heat recovery, most high-performing thermoelectric materials reported in literature are absent in practical applications - partially due to inconsistent synthesis and poor mechanical performance. This work...
When a collection of individual units behave synchronously, it is often useful to describe the actions of the group. Broadly speaking in Physics, individuals are described as particles and collective actions are described using waves. However, the dynamic symphony of life ordains that orchestral sections play in harmony for a...
Understanding the photophysical processes of organic materials is important for utilizing them as functional photonic materials. Typical photophysical processes include intersystem crossing, charge transfer (CT), symmetry-breaking charge separation (SB-CS), singlet fission (SF), etc. There are serval factors that can lead to different photophysical processes, such as the molecular energy levels,...
Recent developments in research concerning organic photovoltaics (OPVs) have overseen massive increases in device performance and the ascension of electron acceptor materials that outclass the preeminent acceptor compounds, buckminsterfullerene (C60) derivatives. New design strategies in the molecular structure of perylenediimides (PDIs) and fused-ring electron acceptors (FREAs) have increased single-junction photovoltaic...
This manuscript describes and contextualizes the research I performed as a PhD student in Northwestern University. The first three chapters, on Markov chains, stochastic thermodynamics, and large deviation theory, describe three interrelated topics that serve as the background for subsequent research detailed in the next three chapters, on understanding the...
Despite the increasing interest in biogenic secondary organic aerosols (SOAs), their role in the climate system remains the greatest source of uncertainty in global models. Cloud formation, critical for the net cooling effect provided by cloud cover, is dependent on the abundance of SOA particles and their ability to activate...
This thesis contains two research projects. The first research project examined the coherent nature of electron transfer in two donor-acceptor dyads – one single acceptor control compound and one dual acceptor molecule of interest. Using transient absorption spectroscopy in the ultraviolet/visible/near-infrared and mid-infrared regions, magnetic field effect experiments, and theoretical...
This thesis presents results on photophysics and spin dynamics of photoactive organic molecules that possess one unpaired electron spin in the ground state and two or three unpaired spins upon photoexcitation. The excited state dynamics of the systems were studied using transient optical absorption spectroscopies and non-Boltzmann population on the...
Recent progress in semiconductor synthesis and photophysics has revealed a host of new materials with exciting properties for applications in optoelectronic devices such as sensors, photovoltaics, solid state lighting, and more. One of the most significant recent additions to the field is the class of hybrid and inorganic materials that...
This dissertation examines the effects of phase transfers with thiol ligands on the optical properties of quantum dots (QDs) in water by investigating two systems: i) dihydrolipoic acid (DHLA)-capped PbS QDs and ii) thiolated DNA-capped core/shell CdSe/CdS QDs. QDs are bright, monodisperse, and tunable hydrophobic nanoparticles with high photoluminescence (PL)...
Semiconductor nanocrystals possess unique photophysical properties that make them desirable for many optoelectronic applications such as photovoltaics, LEDs, and quantum computing. When the size of a semiconductor is reduced to below the excitonic Bohr radius of the material, its carriers becomes quantum confined resulting in drastic changes to optical, electronic,...
Singlet Fission (SF) is a down-conversion process in organic chromophores where one high-energy singlet exciton is converted into two low-energy triplet excitons. Such carrier multiplication aspects of SF are promising in increasing the solar cell efficiency. The generation of two bound spin triplet states from the same singlet exciton also...
How molecular chirality manifests at the nano- to macroscale has been a scientific puzzle since Louis Pasteur discovered biochirality. In general, amphiphilic molecules can organize into a variety of assembly shapes including micelles, spherical vesicles, cylindrical micelles, and planar bilayers. However, when such amphiphilic molecules are chiral, helical ribbons, helicoidal...
The physical boundary layer, or interface, between two different phases of matter is the site of chemical and physical processes that are critical to many research fields. Many of these interfaces contain electric charge, which influences the structure and composition of the interfacial region and the interactions between the interface...
Although electrostatics interactions in fluids have been studied for many decades, new results in this field are still challenging our classical understanding of electrolytes. The combination of electrostatics and self-assembly yields many interesting yet challenging problems that are of fundamental scientific interest and show promise for industrial applications. In this...
This thesis describes the relationships between nanoscale structure and particle transport in two systems: i) the transport and conversion of excitons in colloidal quantum dot (QD) assemblies and ii) the transport of carriers in flashing electron ratchets. One major crux in the creation of efficient photocatalytic systems is the low...
Spin-orbit coupling (SOC) is a powerful phenomenon that dictates the functional properties of transition metal complexes essential for information processing, catalysis, and magnetism. Though it is relegated to lower energy scales within the orbital description of first-row transition metal complexes, SOC impacts crucial aspects of electronic structure such as promoting...
In this thesis, I present the development and benchmarking of several theoretical methods designed to enable the rigorous modeling of magnetic properties of molecules containing one or a few heavy atoms, particularly single-molecule magnets. The new methods use a full four-component treatment of relativity, allowing spin–orbit effects to be taken...
This thesis describes a series of fundamental studies that address the role of electrostatic interactions in modulating i) the permeability of the ligand shell of a colloidal quantum dot (QD) to an anionic redox probe; ii) the resulting yield of photoinduced electron exchange within the QD ‒ redox probe complex;...
Colloidal crystals are promising candidates for nanophotonic applications due to their strong interactions with light and the capability to tailor such interactions through crystal design and engineering. DNA-programmable assembly, in particular, allows for precise structural control down to the sub-nanometer length scale. In this thesis, ways of designing, synthesizing, and...