Theory and Simulations of Charge Transfer in Engineered Chemical Systems

Abstract

<p>Electron transfer is an essential process for life to exist and is the working principle of electronics. Fundamental knowledge of electron transfer is crucial for understanding biological processes and developing future devices. Here, we present our theoretical and experimental efforts to design, synthesize and characterize the electronic properties of charge-transfer complexes and approaches to control their charge flow. </p><p>Computational methods, including wave function-based methods, density functional theory, quantum mechanics/molecular mechanics, and molecular dynamics, were combined with synthesis, ultrafast spectroscopy and conductance measurements to design and characterize engineered chemical systems for efficient charge and energy transfer.</p><p>Compelling foundational questions explored in this dissertation include: 1) Can we control the photoinduced electron transfer rate of molecules with chemically innocent vibrational excitations? 2) Can we create, sustain, and exploit chemical coherences to harvest and transmit energy and information? 3) What chemical modifications lead to enhancing intrinsic charge transport properties of molecular devices?</p><p>First, we discuss the photophysics of highly conjugated organic and organometallic systems consisting of electron donor and acceptor units. Electronic structure calculations combined with ultrafast spectroscopy elucidated the excited-state dynamics of molecular candidates for controlling charge transfer with infrared pulses and directing energy transfer through nonthermal routes. Second, we introduce strategies to fabricate efficient DNA-based molecular wires and obtain abundant semiconducting carbon nanotubes. Molecular dynamics simulations and kinetic modeling revealed the chemical interactions relevant for engineering charge transport in nanostructures. The synergy between our theoretical calculations and experimental measurements provides guidelines to tailor the electronic properties of chemical systems and control charge flow in optically active charge-transfer complexes and nanostructures. </p>