Time-resolved spectroscopy of photosynthetic systems using synchrotron radiation

Chlorophyll fluorescence decay profiles of O3 -exposed spruce needles as measured by time-correlated single photon counting

Chlorophyll fluorescence decay profiles have been measured in the wavelength range 680-720 nm for needles from Norway spruce [Picea abies (L.) Karst] trees which have been exposed to ozone. All profiles required three exponential components of lifetime 100-150 ps, 400-600 ps and 3.5-5.0 ns to fit the experimental data. Compared to control samples, the ozone-treated needles exhibited a greater amount of the longest-lived chlorophyll fluorescence and a redistribution in intensity for both the other components from 720 + to 690 nm. These observations are interpreted in terms of disruption of energy transfer and break-up of light-harvesting complexes on exposure to ozone. The potential for use of the technique in monitoring forest decline is discussed.

Applications of ultrafast laser spectroscopy for the study of biological systems

The discovery of mode-locked laser operation now nearly two decades ago has started a development which enables researchers to probe the dynamics of ultrafast physical and chemical processes at the molecular level on shorter and shorter time scales. Naturally the first applications were in the fields of photophysics and photochemistry where it was then possible for the first time to probe electronic and vibrational relaxation processes on a sub-nanosecond timescale. The development went from lasers producing pulses of many picoseconds to the shortest pulses which are at present just a few femtoseconds long. Soon after their discovery ultrashort pulses were applied also to biological systems which has revealed a wealth of information contributing to our understanding of a broadrange of biological processes on the molecular level.It is the aim of this review to discuss the recent advances and point out some future trends in the study of ultrafast processes in biological systems using laser techniques. The emphasis will be mainly on new results obtained during the last 5 or 6 years. The term ultrafast means that I shall restrict myself to sub-nanosecond processes with a few exceptions.