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 ∼100 fs, which then decays to zero in a time scale of ∼2 ps.