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RESEARCH PRODUCT

Characterisation of Chlorophyll a and Chlorophyll b Monomers in Various Solvent Environments with Ultrafast Spectroscopy

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In photosynthesis the energy from the sun is captured by light harvesting chlorophyll pigments and converted to stable chemical energy, by the photochemical reaction center. Photosynthetic energy transfer in the antenna systems of green plants has previously been studied by ultrafast time resolved spectroscopy. The characteristics of the chlorophyll pigments itself is important to study in order to understand the dynamics on a femtosecond timescale. One way to study the energy transfer is to use transient absorption spectroscopy and follow the increase or decrease in the transient absorption signal with time (1). Another way to study the energy transfer is to monitor the change in dichroism with time, following excitation with a short pulse of light, caused by the different orientation of the transition dipole moments at different chlorophyll molecules. This has been done for different light harvesting complexes (1), by measuring the anisotropy of the transient absorption signal. In this study we investigated how the initial (t=0) anisotropy signal depends on the probe wavelength and calculated the relative contributions of ground state bleaching, stimulated emission and excited state absorption to the transient absorption signal. This was done for chlorophyll a in pyridine and chlorophyll b in pyridine + 3-methylpentane. Pyridine was used as a solvent to make sure that we had monomers of the chlorophylls and no aggregation.