Measuring the spectral diffusion of chlorophyll a using two-dimensional electronic spectroscopy

Area of Science:

• Physical Chemistry
• Spectroscopy
• Biophysics

Background:

• Chlorophyll a is a crucial pigment in photosynthesis.
• Understanding its spectral dynamics is key to photosynthesis research.
• Solvation dynamics influence light-harvesting processes.

Purpose of the Study:

• To investigate the spectral diffusion of the Qy transition of chlorophyll a in methanol.
• To characterize the time scales of solvation dynamics affecting chlorophyll a.
• To differentiate between inertial solvation, diffusive processes, and structural inhomogeneity.

Main Methods:

• Utilized ultrafast two-dimensional electronic spectroscopy (2D ES).
• Employed the center line slope (CLS) method to measure the two-time frequency-fluctuation correlation function (FFCF).
• Optimized fitting of the linear spectrum was used in conjunction with CLS.

Main Results:

• The FFCF of the Qy transition exhibited decay over four distinct time scales.
• Identified three fast time constants: ~65 fs (inertial solvation), ~0.5 ps, and ~7 ps (spectrally diffusive solvation).
• A slower time constant (>1 ns) was attributed to chromophore structural inhomogeneity.

Conclusions:

• Spectral diffusion of chlorophyll a in methanol is a multi-timescale process.
• Fast dynamics are dominated by inertial and diffusive solvation.
• Longer time scales indicate contributions from chromophore structural variations.