Amy Scott

Northwestern University
2145 Sheridan Road
Ryan Hall 1033
Office telephone number: 847-467-4948
Laser lab telephone number: 847-467-7653

e-mail: a-vega@northwestern.edu

Education:

ACS Certified BS in Chemistry with high distinction from the University of Colorado at Colorado Springs.

Publications:

E.T. Chernick, Q. Mi, A.M. Vega , J.V. Lockard, M.A. Ratner, M.R. Wasielewski. “Controlling Electron Transfer Dynamics in Donor-Bridge-Acceptor Molecules by Increasing Unpaired Spin Density on the Bridge,” Journal of Physical Chemistry B , 2007 , 111 , 6728

L. Kondrachova, K.E. Paris, P.C. Sanchez, A.M.Vega, Pyati, R., “Electrochemical Investigations of Platinum Phenyethynyl Complexes,” J. Electroanal. Chem., 2005, 576, 287

Amy M. Scott and Radha Pyati , “Solvent Viscosity and Interrelated Effects on Electrochemiluminescence Intensity of Tris (2,2’-bipyridyl) Ruthenium(II),” J. Phys. Chem. B., 2001, 105, 9011.

I study photoinduced electron transfer through organic donor-bridge-acceptor molecules using nanosecond transient absorption and magnetic field effect. Understanding fundamental charge transfer and spin transfer processes will allow us to utilize organic materials for solar cells, molecular electronic devices, and spintronics. More specifically, charge transport over long distances and the transporting medium (i.e. in this case the phenyl bridge) is important when designing efficient photonic devices. We have previously designed a series of PTZ-Ph n-PDI molecules that upon photoexcitation of the D-B-A system, subsequent ET results in a solvent stabilized radical pair (RP) with wire-like charge recombination. In our newly designed system (fig 1) the high energy and restricted nature of the donor play a role in charge transfer dynamics and charge recombination occurs via superexchange mechanism.

In organic systems where spin-orbit intersystem crossing (SO-ISC) is inefficient, the RP is generated initially in a spin-correlated singlet configuration. Spin evolution occurs as the radical pair experiences local nuclear hyperfine interactions, on the nanosecond timescale, that induces radical pair–intersystem crossing (RP-ISC) to the triplet state. The energy difference between the singlet and triplet energy levels of the RP results from an exchange interaction, 2J, between the two spins. The magnitude of 2J can be related to V DA to approximate the bonding interaction of the singlet and triplet states with their surrounding states. When an external magnetic field is applied, the Zeeman splitting between the triplet sublevels T i (i =-1,0,-1) occurs. Modulation of the RP-ISC rate with applied external magnetic field results in a 2J resonance, as the triplet sublevels becomes isoenergetic with the single RP state and the rate maximizes at that field. 8, 9 The treatment of these effects is described by the Radical Pair Mechanism (RPM). Direct measurement of 2J is obtained by monitoring the triplet yield with applied magnetic field and gives information on the electron coupling of the donor and acceptor (see figure 3).

Temperature dependent MFE on DMJ-An-Ph 2-NI shows that lowering the temperature below 250 K reveals two resonances that contain two distinct electronic couplings. At 170 K the prominent 2J resonance appears at 1.5 mT and the other 2J feature at 43 mT diminishes into a broadened peak. Previous studies on a similar D-B-A triad with conformational freedom attribute the existence of two resonances to different, stable conformations when the equilibrium constant is changed with temperature