Robin Main Hochstrasser (1931–2013), giant of physical chemistry

When Robin Main Hochstrasser died on February 27, 2013, science lost one of its truly great physical chemists: a pioneer in the application of lasers in chemistry. Using advanced laser-based techniques to address questions of molecular structure and dynamics, Robin’s work impacted all branches of chemistry. His trademark was creativity, repeatedly managing to carry out totally new kinds of experiments thought by his peers to be impossible at the time. The result was a constant stream of ground-breaking experiments and novel ideas from the early 1960s to just a few months ago. Because of the depth and breadth of his research, Robin left his mark on science, not only by his own original research, but also by inspiring and creating many scientific opportunities for others.

• Download figure
• Open in new tab
• Download powerpoint

Robin Hochstrasser with his daughter Jennie in Moscow, June 1990.

Robin possessed a larger-than-life personality and an immense intellect that was a major force in the lives of three generations of scientists. As a faculty member at the University of Pennsylvania for 50 years, he trained 75 doctoral students, including a Nobel Laureate, Ahmed Zewail, and more than 90 postdoctoral fellows. Beyond his laboratory, Robin’s influence on the whole scientific community was extraordinary, often challenging colleagues with insightful questions and inspiring them to think more deeply and to do even better work. At a memorial service attended by several hundred people at the University of Pennsylvania on April 4—many traveling long distances—eminent scientists, including David Chandler, Graham Fleming, Charles Harris, Harvey Rubin, Charles Shank, and Amos Smith, emphasized this characteristic of Robin in their public remarks.

Robin Hochstrasser was born and educated in Edinburgh, Scotland. His education as a teenager was unconventional, as he dropped out of high school at age 15 and spent a year mostly shooting pool. After receiving private lessons and taking special courses, Robin passed the college entrance examinations (with perfect scores in mathematics and chemistry), and received his Bachelor of Science degree from Heriot-Watt University in 1952 and his doctorate in chemistry from the University of Edinburgh in 1955. His thesis on photochemistry was supervised by Mowbray Ritchie. Following two years as an officer in the British Royal Air Force, Robin joined the faculty at the University of British Columbia in 1957, first as Instructor and then as Assistant Professor in 1960. During this period, he also worked at the National Research Council in Ottawa, Canada and at Florida State University with Michael Kasha. Robin moved to the University of Pennsylvania in 1963, where from 1968 he was the Blanchard Professor and, since 1983, the Donner Professor of Physical Sciences. Robin was Editor of Chemical Physics since 1975, and a Special Issue of this journal dedicated to him on the occasion of his retirement as editor in 2012 will soon appear. From 1979 Robin was Director of the Ultrafast Laser Research Resource, a national resource sponsored by the National Institutes of Health for the development and application of advanced laser technologies to problems in biomedicine. His other professional positions included visiting professorships at universities in Cambridge (United Kingdom), Canberra, Pasadena, Munich, Oxford, Paris, and Grenoble, and Chair of the John Scott Advisory Panel for the City of Philadelphia from 1988 to 2010.

With his arrival in 1963, Robin brought modern spectroscopy to the University of Pennsylvania. He decided to study molecules, oriented in crystals, under applied magnetic and electric fields, and characterized excited states and their coupling by analyzing Zeeman and Stark effects in the high-resolution spectra obtained at low temperatures. Robin brought modern quantum mechanical thinking to understand the much less-resolved broad-banded spectra that molecules exhibited in solution by showing how the effects of intramolecular state coupling and damping influence the shapes of molecular spectra, and demonstrated the role of damping in relating resonance Raman and fluorescence spectroscopies. This early work was extremely influential in moving molecular spectroscopy from the gas phase to the condensed phase. For the next almost five decades, Robin’s experiments and ideas created new areas of research in condensed phase chemistry. He published more than 500 original scientific papers and two books, Behavior of Electrons in Atoms (1) and Molecular Aspects of Symmetry (2).

In the late 1960s Robin, along with just a few other chemists worldwide, began to adapt various types of lasers for investigating molecules and created the “lasers in chemistry” revolution that continues to this day. From the birth of picosecond and femtosecond lasers, Robin realized that they could be used to gain a deeper understanding of molecular structure and dynamics. Just a few examples of Robin’s dozens of “firsts” include direct measurement of the redistribution of vibrational energy in an isolated molecule, of vibrational relaxation in liquids and molecular solids, and of a two-photon electronic spectrum of a molecule using a tunable dye laser. All of this work was accompanied by a deep understanding of the underlying theoretical concepts. In a classic Hochstrasser experiment in the 1980s, he was one of the first to observe the long sought after turnover of the rate as a function of friction predicted by Kramer’s theory for chemical reaction rates, by studying the isomerization reaction of an organic molecule as a function of pressure, density, and viscosity.

In addition to his fundamental research in physical chemistry, Robin, more than any other scientist, showed that it was possible to carry out spectroscopic experiments on large molecules, such as proteins, with the same rigor as research on small molecules. A beautiful example was his discovery in the late 1970s that when the iron-oxygen bond of hemoglobin breaks upon electronic excitation with a picosecond laser pulse, most of the oxygen rebinds in a unimolecular process on a subnanosecond time scale before escaping into the solvent and rebinding in a bimolecular process. This phenomenon, known as geminate recombination, has been key to understanding how hemoglobin binds oxygen cooperatively; at the same time, these experiments, using a picosecond laser continuum for measuring complete spectra, set a new standard for time-resolved spectroscopic measurements and opened up an entire new field of research in biophysical chemistry. In the 1980s Robin carried out ground-breaking work using femtosecond infrared laser pulses to monitor the changes in vibrational spectra of carbon monoxide moving inside hemoglobin. These were the first femtosecond time-scale measurements observed through vibrational spectra. This work was followed by his invention of a powerful new technique, 2D infrared (IR) spectroscopy in the late 1990s at an age when most scientists have effectively retired. Two-dimensional IR has changed the direction of research in dozens of laboratories around the world. Unlike 1D IR, in which structures are characterized by empirical correlations, 2D IR, like multidimensional NMR spectroscopy, yields 3D structure and dynamics by revealing the couplings between vibrational modes. However, nonequilibrium 2D IR experiments can be performed with at least nine orders-of-magnitude better time resolution than NMR. By means of isotope replacement experiments, Robin carried out extensive studies of the structures and dynamics of small peptides, α-helices, both globular and transmembrane proteins, and most recently, amyloid fibrils found in Alzheimer’s patients.

What was particularly unusual about Robin is that he was still developing state-of-the-art technology and producing forefront research into his 80s. He barely slowed down, even though he knew two years ago that he had a fatal illness. Unlike almost any other scientist at his age, the number of citations to Robin’s publications per year was still on the rise. Robin died “with his boots on.” One of his very last publications was an article in the March 2013 issue of Nature Chemistry (3), which also received a News and Views and was featured on the cover of the journal, a publication “hat trick.” In this work, Robin identified the molecular interactions between an AIDS drug and the enzyme reverse-transcriptase of HIV that explains how this molecule overcomes drug-resistant mutations.

Robin’s research contributions were recognized by many honors and prestigious awards, including election to the National Academy of Sciences in 1982, the year he became a naturalized citizen, the Benjamin Franklin Medal in Chemistry, the Centenary Silver Medal of the Royal Society of Chemistry, and National Awards of the American Chemical Society: the E. Bright Wilson Award in Spectroscopy and the Peter Debye Award in Physical Chemistry.

We were both very close friends of Robin and the Hochstrasser family for more than 40 years, so we witnessed all sides of Robin, both professionally and personally. What attracted us and so many people to him was that he was such an incredibly smart person with a sophisticated and often hilarious sense of humor. He had a lot of style and a ton of charisma. Robin did everything with great gusto, whether it was watching sports or playing sports—tennis, golf, skiing—playing bridge, shooting pool, discussing politics, or playing chess with his grandson. Although he very much enjoyed traveling all over Europe and spending sabbaticals in England, Germany, and Italy, Robin was a thorough Francophile. He loved French culture, French food and wine— he had an impressive collection of French wines—and spoke the language well enough to give scientific lectures in French.

Dinner with Robin was always a special event, because as many scientists know, Robin knew a great deal about food and wine and was a gourmet chef. There is objective evidence of Robin’s fine palate. In 1988 when Robin was on sabbatical leave in Paris, he and one of us made a one-day trip to the champagne country, stopping at various vineyards to sample their champagne. A stop at one small vineyard in Damery was the most interesting. Robin was making such insightful comments that the owner kept offering him better and better quality champagne. Impressed with what Robin had to say, the owner asked Robin if he could hire him as a taster for those critical times when the sweetness of the champagne is adjusted just before the final corking of the bottles. For a moment Robin actually considered accepting the job.

Robin was an extremely courageous soul. We knew, and he knew, that when he received the dreadful diagnosis of idiopathic pulmonary fibrosis that he would live for no more than two years. He managed to conceal this¸ and carried on in public as though he were in good health until he finally required a wheel chair to get around two months before he died. In our many, many conversations during these two past years, Robin never once uttered a complaint or expressed a fear of dying. Finally, if we had to characterize Robin in a single sentence, we would say that it was always extremely interesting, very rewarding, and simply great fun to be with him in any situation. There was never a dull moment with Robin in the room. His passing has left a gigantic hole not only in our lives but the lives of so many others.