Measuring the Spectral Diffusion of Chlorophyll a Using Two-Dimensional Electronic Spectroscopy

Ultrafast two-dimensional electronic spectroscopy has been used to study the spectral diffusion of the Q(y) transition of chlorophyll a in methanol. The two time frequency-fluctuation correlation function (FFCF) of the transition has been measured using the center line slope method, together with optimized fitting of the linear spectrum. The FFCF was measured to decay over four time scales. The three fastest time constants of which were measured to be similar to 65 fs, similar to 0.5 ps, and similar to 7 ps. These are assigned as the inertial component of solvation and spectrally diffusive solvation processes respectively. The fourth time constant (>1 ns) may be attributed to the chromophore structural inhomogeneity.