Measuring the Ultrafast Correlation Dynamics between the Q x and Q y Bands in Chlorophyll Molecules.

We use two-dimensional electronic spectroscopy to measure the ultrafast correlation dynamics between the Q(x) and Q(y) transitions in chlorophyll molecules. We derive a variation to the center line slope method to quantify the frequency fluctuation cross-correlation function, C-xy(T-w). Compared with the frequency fluctuation correlation function of the Q(y) transition, we observe that there is only a minimal correlation between the Q(x) and Q(y) transition, even at the ultrashort timescale of similar to 100 fs, which then decays to zero in a time scale of similar to 2 ps.