Photosynthesis begins with the absorption of sunlight by a set of colorful molecules, mainly chlorophyll. They enable transfer of the absorbed energy to the places in the photosynthetic cell where primary chemical reactions will take place. It is this part of photosynthesis, preceding the chemical steps, that interests us. The time involved in the physical transfer process is quite small (about 100 picoseconds).
Our research is theoretical, but we work closely with experimental groups. Exciton theory is used to study photosynthetic systems by predicting their rates of energy flow, their ultrafast optical properties, and their overall efficiencies. This work in biological physics can be described as molecular physics, or chemical physics, or even condensed matter physics, but its focus is on the complex apparatus of photosynthetic systems.
We have developed a generalization of the theory of Kennard and Stepanov, sometimes known as the "Universal Relation," connecting fluorsecence and absorption spectra. See R. S. Knox, Acta Physica Polonica 95, 85 (1999) for references and an introduction. On the basis of this extended theory as applied to observed spectra, we have hypothesized a new fluorescing state of the chlorophyll molecule.
Global warming is directly affected by photosynthesis because of the continuous exchange of oxygen and carbon dioxide between plants and the atmosphere. In addition to the well-known effects of human activity on the chemical composition of the atmosphere, there is a possibility that over-usage of the non-solar energy will also have an effect on global temperature. While this effect is currently down in the noise, we consider it important to study, since it relates to the urban heat island effect on a local basis. An update of the old but useful Arrhenius model of global warming has been made [Phys. Lett. A 329, 250-256, 2004]. Code for the model used is available in spreadsheet form, as an Excel(TM) workbook GlobalModel. If you intend to use this spreadsheet, see the ReadMe file. More recently, we have pointed out an interesting anomaly in the temperature profiles above Iceland, and have used an energy balance model to interpret globally-averaged temperature data taken during the Pinatubo volcano eruption of 1991.
"Thermocline flux exchange during the Pinatubo event," D. H. Douglass, R. S. Knox, B. D. Pearson, and A. Clark, Jr., Geophys. Res. Lett. 33, L19711, doi:10.1029/2006GL026355 (2006)
“Climate forcing by the volcanic eruption of Mount Pinatubo,” David Douglass and Robert S. Knox, Geophys. Res. Lett. 32, L05710, doi:10.1029/2004GL022119 (5 p.) (2005)
“Iceland as a heat island,” D. H. Douglass, V. Patel, and R. S. Knox, Geophys. Res. Lett. 32, L03709, doi:10.1029/2004GL021816 (4 p.) (2005)
"Excited-state energy transfer in covalently linked multiporphyrin arrays: the essential contribution of energy transfer between nonadjacent chromophores," E. Hindin, R. A. Forties, R. S. Loewe, A. Ambroise, C. Kirmaier, D. F. Bocian, J. S. Lindsey, D. Holten, and R. S. Knox, J. Phys. Chem. B, 108, 12821-12832 (2004)
"Non-radiative energy flow in elementary climate models," R. S. Knox, Phys. Lett. A 329, 250-256 (2004)
"Temperature response of Earth to the annual solar irradiance cycle," D. H. Douglass, E. G. Blackman, and R. S. Knox, Phys. Lett. A 323, 315-322 (2004); corrigendum ibid. 325, 175-176 (2004)
"Comparison of excited-state energy transfer in arrays of hydroporphyrins (chlorins, oxochlorins) versus porphyrins: rates, mechanisms, and design criteria," M. Taniguchi, D. Ra, C. Kirmaier, E. Hindin, J. K. Schwartz, J. R. Diers, R. S. Knox, D. F. Bocian, J. S. Lindsey, and D. Holten. J. Amer. Chem. Soc. 125, 13461-13470 (2003)
"Development of an elementary climate model: two-layer cellular case," L. E. Schmidt, H. L. Helfer, and R. S. Knox, posted in physics archive, http://arXiv.org/abs/physics/0308061 (Aug. 15, 2003)
"Dipole strengths in the chlorophylls," R. S. Knox and B. Q. Spring, Photochem. and Photobiol. 77, 497-501 (2003).