Abstract
Measurements of ultrafast transient processes, of temporal durations in the picosecond and femtosecond regime, are made possible by femtosecond pump probe transient absorption spectroscopy. Such an ultrafast pump probe transient absorption setup has been implemented at the CSIR National Laser Centre and has been applied to investigate energy transfer processes in different parts of photosynthetic systems. In this paper we report on our first results obtained with Malachite green as a benchmark. Malachite green was chosen because the lifetime of its excited state is well known. We also present experimental results of the ultrafast energy transfer of light-harvesting complexes in samples prepared from spinach leaves. Various pump wavelengths in the range 600–680 nm were used; the probe was a white light continuum spanning 420–700 nm. The experimental setup is described in detail in this paper. Results obtained with these samples are consistent with those expected and achieved by other researchers in this field.
Highlights
Photosynthesis is the process by which light energy is converted into chemical energy and through a complex series of biochemical and biophysical processes, to any one of a number of bio-machines.[1]
Circular dichroism measurements Circular dichroism (CD) was measured at room temperature using the Chirascan Circular Dichroism Spectrometer (Applied Photophysics) and the results can be presented in units of absorbance or millidegrees
The asymmetric bands at ~430–505 nm and ~675 nm indicate the formation of large macro-aggregates with long-range chiral order within the sample, which allows energy transfer
Summary
Photosynthesis is the process by which light energy is converted into chemical energy and through a complex series of biochemical and biophysical processes, to any one of a number of bio-machines.[1] There is a large diversity of photosynthetic organisms—higher plants, cyanobacteria and photosynthetic bacteria2 —for which some fundamental processes are common These are light absorption, excitation energy transfer, charge separation and vectoral charge transfer.[1] In the photosynthetic process, chlorophylls are light-absorbing pigments which bind to proteins and are known as pigment proteins. Many biological and chemical processes occur on relatively long time scales (from milliseconds to seconds) These long processes are the result of combinations of several very fast elementary processes ranging from femtoseconds to picoseconds.[33] This generally is referred to as the ultrafast or ultrashort pulse regime. Femtosecond transient absorption (pump probe) spectroscopy has become a widely-used and useful technique for studying ultrafast processes.[34]
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