Dr. David McCamant
From Denver, Colorado
Office: 1031 Nano, (847) 467-4944
Laser Lab: B011 Nano (847) 467-7653 and 467-2173
I am currently researching electron transfer dynamics in donor-bridge-acceptor molecules and in molecules containing an additional unpaired radical spin. The primary optical techniques I utilize are time-resolved fluorescence (TRF) and femtosecond transient absorption (fsTA).
I am studying the charge separation and recombination dynamics between a photoexcited julolidine-anthracene (JA) electron donor and a naphthalene-diimide (NI) electron acceptor, which are joined by an oligophenylene (n=1-5) bridge. We use transient absorption to observe the charge separation and recombination events by measuring the time-dependent rise and fall of the unique JA* excited state and subsequent NI anion absorption spectra following photoexcitation with a 100-fs laser pulse.
Radical Perturbed Electron Transfer:
We and others have observed the effect of external magnetic fields on the electron spin and charge recombination dynamics in donor-acceptor molecules.(1) This occurs primarily through an enhancement of the radical-pair intersystem crossing (RP-ISC) which can change the relative population of the radical pair singlet (net electron spin = 0) and triplet (net electron spin = 1) states, each of which will exhibit a unique spin-selective recombination rate. An additional way to induce this magnetic field effect is with the addition of a single unpaired electron (a “radical”) nearby the charge-separating species.(2) My colleague, Erin Chernick, has been able to successfully synthesize a variety of unique donor-bridge-acceptor-radical and donor-(radical bridge)-acceptor molecules. We are currently studying the ultrafast electron transfer dynamics in these unique systems.
(1) Weiss et al. J. Am. Chem. Soc.2004, 126, 9510-9511.
(2) Weiss et al. J. Am. Chem. Soc.2004, 126, 2326-2327.
Figure 2 - Kinetics of growth of NI •- signal in JA-ph n-NI compounds. Each intensity has been normalized for ground-state absorption and is calculated as the average intensity from 465-485 nm. The negative feature at Dt< 0.5 ps is due to stimulated Raman signal from the solvent. The charge separation time-constants are noted in parenthesis.