This chapter discusses some of the techniques used in picoseconds spectroscopy and the impact the results have on the understanding of biological processes. The initial events of chemical and biological reactions occur during times ranging from less than one picosecond to greater than one nanosecond. It has been important, therefore, to develop means for investigating reaction kinetics on this time scale. Techniques for producing and characterizing picosecond pulses and for measuring ultrafast emission and absorption spectra have evolved during the past fourteen years so that these events can be probed with a temporal resolution of about one picosecond. The application of these techniques to biological systems has provided new information and has led to a better understanding of the primary processes involved in vision, photosynthesis, and energy relaxation mechanisms in porphyrins and the kinetics of photodissociation and ligand rebinding of heme proteins. The chapter restricts the description to the experimental systems used for probing the ultrafast kinetics of photobiology. The major components of the experiment are for (1) the generation of a picosecond pulse, (2) the conversion of that pulse into a wavelength appropriate for excitation, and (3) data collection and processing. The chapter explains both areas of picoseconds spectroscopy, absorption and emission. Emission experiments involve the collection and measurement of the time evolution and wavelength characteristics of the light emitted by excited states of the system. Absorption experiments, however, involve the measurement of the reaction kinetics as reflected by absorption changes at various wavelengths. The most extensive picosecond biological studies have been done on vision and bacteriochlorophyll; lately considerable interest has also been developed in the energy relaxation mechanisms of porphyrins and heme proteins. The chapter discusses each of these topics in brief. 1980, Academic Press Inc. (London) Ltd.
