Photosynthesis Research 80: 71–76, 2004. 71 © 2004 Kluwer Academic Publishers. Printed in the Netherlands. Tribute The contributions of James Franck to photosynthesis research: atribute Jerome L. Rosenberg Office of General Counsel, University of Pittsburgh, Pittsburgh, PA 15260, USA (e-mail: [email protected]; fax: +1-412-624-1606) Received 21 May 2003; accepted in revised form 4 June 2003 Key words: Zolton Bay and Robert Pearlstein, Niels Bohr, Warren Butler, excitation transfer, fluorescence, James Franck, Hans Gaffron, Karl Herzfeld, Eugene Rabinowitch, Edward Teller Abstract The scientific career of James Franck (26 August 1882–21 May 1964) spanned seven decades in which he was preoccupied with understanding the interaction of light with matter, starting with atoms and moving to the photosynthetic apparatus in green plants. The 1926 Nobel Prize in physics demonstration of the quantization of electronic states in molecules, photodissociation of molecules, the In a sense, James Franck’s (Figures 1 and 2) earli- quantization of energy in atomic and molecular fluo- est scientific contributions to photosynthesis were his rescence, and the first demonstration of sensitized experimental results that would lead to an under- fluorescence of an emitting species following absorp- standing of molecular photochemistry, begun almost tion of light by a different donor substance (Franck a century ago. An experimental physicist working 1923) and of sensitized photochemistry (Cario and in Berlin, Franck published his first papers with Franck 1922). His studies of polarization of fluo- Gustav Hertz on the collisions between electrons and rescence provided an early experimental method for gaseous atoms (Franck and Hertz 1914a, b). This determining the lifetime of fluorescent states. Other work was a demonstration of the existence of dis- important discoveries of that period which would have crete energy levels of excited electronic states of atoms an impact on much later work in photosynthesis re- and provided confirmation of Niels Bohr’s theoret- search included an analysis, supplemented by Edward ical proposal for the quantization of atomic energy Condon, of the shape of molecular absorption and levels. Franck and Hertz were jointly awarded the fluorescence spectra (Franck 1925; Condon 1926). Nobel Prize for this work in 1926. (For a discussion This is known as the Franck–Condon principle and is of the life and major discoveries of Franck, see Kuhn based on the rapidity of electronic transitions in con- 1965.) trast to the slower equilibration of the heavier nuclei that follows. Franck originally used this principle to explain the photodissociation of molecules, and Con- Discovery of sensitized don extended the principle to rationalize the shapes fluorescence and photochemistry of absorption and fluorescence bands, including the and of the Franck–Condon principle Stokes shift (named after Sir G.G. Stokes): the red shift of the fluorescence emission from that of the A continuation of these investigations over the fol- absorption maximum. Other findings of that period lowing two decades, first at Berlin and later at the included an understanding of competing processes for University of Göttingen, included an experimental de-excitation of higher electronic states of molecules, 72 Figure 3. Photograph of the author, Jerry Rosenberg, and his wife Shoshana. Political dissent in Germany Franck’s 12 productive years at Göttingen ended in Figure 1. A photograph of James Franck by Lotte Meitner-Graf, 1933 with his forthright entry into the arena of polit- daughter of Lisa Meitner, a colleague of Franck from his German ical dissent. His resignation from his professorship days. as a public protest against emerging Nazism became a cause celebre in Germany. Although his World War I army service would have spared him from dismissal from his post under the new anti-Semitic laws, although only for the short term as we now know, he refused to accept his orders to dismiss many of his faculty, staff, and students under the new edicts dealing with racial and ‘politically cor- rect’ classifications. Instead, he worked tirelessly as a private citizen from his home in Göttingen to locate scientific employment opportunities throughout the Western world for dozens of his colleagues. One of the beneficiaries of this activity was Eugene Rabinowitch, who spent some time with Niels Bohr (see Bannister 1972). Transition years Franck had a brief sojourn in Niels Bohr’s labora- tory in Copenhagen. One of his important papers from this period was his work with Eugene Rabinowitch Figure 2. From a portrait of James Franck painted by Martyl from photographs and from memory. The painting, hanging in the James (Franck and Rabinowitch 1934) on solution effects in Franck Institute at the University of Chicago, was unveiled in 1983, photochemical processes, in which rules for recombi- close to the 100th anniversary of James Franck’s birth. nation of photodissociation products were worked out. Here, the quantum yield of the photo-dissociation including internal conversion and the role of meta- in a liquid may be less than in the gas phase be- stable states. (These Franck publications, mostly in cause the primary photodissociation fragments, un- German, are summarized in Kuhn 1965.) able to escape the liquid ‘cage’ surrounding them, 73 may undergo recombination before the finishing reac- At Chicago, some of his early collaborators were tion can take place. Franck’s modesty did not allow visiting scientists, including the photochemist Robert him to refer to this work by its common name, the Livingston, the plant physiologist Allan Brown, and Franck–Rabinowitch cage effect. Instead, he used several younger scientists just beginning their research the term ‘the so-called Franck–Rabinowitch effect,’ careers, including C. Stacy French and Ted Puck, just as he always referred to his earlier work on followed after World War II by Henry Linschitz. I the shape of molecular absorption and fluorescence (Figure 3) joined the group in my first postdoctoral bands in terms of the ‘so-called Franck–Condon prin- position in 1949. Of Franck’s graduate students, most ciple.’ continued in scientific careers, including Sol Weller, George Zimmerman, Leonard Tolmach, John Brugger, Frank Allen and Sanford Lipsky. Best known to those Immigration to the United States and entry in photosynthesis research was Franck’s last doctoral into photosynthesis research student, Warren Butler (see Benson 1998, for Butler’s biography). Franck came to the United States in 1935, first to Johns Hopkins University in Baltimore, and later, in 1938, The Franck Report to the University of Chicago as Professor of Physical Chemistry. Franck began to think about turning his at- Franck’s second major foray into the public arena de- tention to photosynthesis at the time of his move to the veloped from his role as chairman of the Committee on United States. Perhaps he was discouraged about the Social and Political Implications of Atomic Energy, a prospects of setting up a modern laboratory in atomic small group of scientists working at the Metallurgical and molecular physics. A more likely explanation is Laboratory, the Chicago arm of the Manhattan Project that in 1938, at the age of 56, he felt challenged to which was formed by the US government near the be- tackle the major problem of photobiology. The Samuel ginning of World War II to develop nuclear weapons. Fels Foundation established a laboratory in photosyn- This committee issued its findings and recommenda- thesis for him in 1938 at the University of Chicago, tions in what came to be known as the Franck Report, where he became Professor of Physical Chemistry. delivered personally by Franck to the US Secretary Within a year he invited Hans Gaffron (for some of War Henry Stimson on 11 June 1945, shortly be- of the contributions of Gaffron, see Homann 2003) fore the detonation of the first nuclear test bomb in to join him, and the two constituted an interesting New Mexico. The report predicted a nuclear arms complementary pair, one emphasizing physical mech- race that would follow the introduction of this new anisms and the other comparative biochemistry and weapon into warfare and a concomitant threat to the plant physiology. security of all nations, including the United States. The report called for the first use of this weapon as a pre-announced demonstration release in an uninhab- Collaborators ited area. Although the chief recommendation of the report was not accepted, this episode reflects on the Franck continued a pattern established in Germany seriousness of purpose and of concern for human wel- of working with colleagues with whom he could fare shown by Franck and the other authors of this jointly think out a variety of explanations for com- historical document (Rabinowitch 1964). plex problems. His earliest senior co-workers in the area of photosynthesis in his brief sojourn at Johns Hopkins were physicists – the experimental spec- Photosynthesis research troscopist R.W. Wood and two theoreticians, Karl Herzfeld and Edward Teller. The papers with these Franck’s experimental work in photosynthesis dealt three were in the areas of chlorophyll fluores- mainly with chlorophyll fluorescence (Franck et al. cence (Franck and Wood 1936), general photo- 1941; Shiao and Franck 1947); flashing light exper- synthetic theory (Franck and Herzfeld 1937), and iments (Weller and Franck 1941); and ‘afterglow’ electronic energy migration (Franck and Teller 1938), (Brugger and Franck 1958). He spent most of his time respectively. and energy, however, in attempting to construct an 74 overall theory of photosynthesis consistent with the to all the technical discoveries and improvements of major observations, largely made by others. From his the past six decades, including the detailed exploita- first major paper with Herzfeld (Franck and Herzfeld tion of 14C as a tracer in the carbon pathway, the 1937) to his final one, with the author (Franck and technology of very short light flashes, the improve- Rosenberg 1964), his theories had some explana- ment in ‘monochromaticizing’ incident and emitted tory validity at the time they were advanced but often light, and the isolation and analysis of reaction centers.