Professor David Blank

These researchers are using MSI for three projects.

• Two-photon absorption: MSI systems are used in several ways to analyze the behavior of two photon-absorption in caged molecules. The two-photon absorption spectrum of roughly 20 distinct molecular structures targeted at two-photon ungaging of biologically active therapeutics will be computed. The structure of each molecule is optimized using Gaussian 09. The optimized structures are then fed into Dalton, a quantum chemistry program, and spectra for both the one- and two-photon absorption of the molecules are calculated. This computational work will focus on a new set of biologically relevant molecules that are being synthesized in Professor Mark Distefano's group. The computational predictions will be directly compared with experimental measurements of two-photon absorption spectra.
• Energy transfer: A detailed knowledge of how energy moves in organic materials is critical to understanding and improving the efficiency of organic electronic devices. However, the factors that govern the motion of energy in these materials are complex. The quantum mechanical couplings that are relevant for determining simple bimolecular energy transfer events are typically modulated by structural variation on spanning the nano- and micro-meter length scales. Because of this complex interdependence between local structure and electronic coupling, the device relevant perspective of energy transport cannot be accurately modeled with analytic formulas based on continuum or lattice models. Realistic material structures must be generated and used directly with simulations which account for all the microscopic rates of energy transfer. These simulations are based on the kinetic Monte Carlo technique and can be used to great effect to understand the coupling of structure and the motion of energy. Though the simulations themselves are conceptually simple, this simplicity comes at the the expense of being computationally demanding. Conveniently, the kinetic Monte Carlo simulations can be easily implemented for parallel computing. Studies seek to understand how the orientational disorder of the lattice and the anisotropy of the energy transfer rates effect the measured diffusion length of the iconic phthalocyanine-based materials. Further studies will investigate how these factors effect the exciton annihilation observed in ultrafast transient absorption studies. Through these simulations we hope to connect our experiments more directly to the microscopic factors that govern the motion of energy in organic electronic materials.

• Intersystem crossing and spin-orbit coupling: To better understand the formation of triplets in a series of molecular dyads, the ORCA compuational chemistry package is being used to calculate the spin-orbit coupling. Some of these systems are designed to enhance triplet yields using a ping-pong type mechanism, where energy is transfered from the primary chromophore to a covalently bound moiety that undergoes intersystem crossing and then returns the energy in the form of a triplet.