Restless Pioneer

Robin M. Hochstrasser, Donner Professor of Physical Sciences, leaves behind a trail of breakthroughs.
April 2013

Some scientists are content to spend their careers doing good, solid work, not breaking much new ground but building upon the foundations laid by others, making small and quiet contributions where they can. Others burst into the limelight early in their careers with a major discovery or theory that shakes their field to its roots, then spend the rest of their lives basking in the singular glow of that achievement.

Robin Hochstrasser, who died February 27, was neither type. The Donner Professor of Physical Sciences was that rare breed of scientist who forged an entirely new direction in his chosen field, physical chemistry, and then spent the rest of his life building and expanding upon the possibilities created by the breakthroughs he had authored. Along the way, he led innumerable other scientists to their full potential and countless new discoveries.

For most chemists, Hochstrasser's name is synonymous with laser spectroscopy, and for good reason: He was one of the pioneers of the field, beginning not long after the laser itself was invented. "He was a very early adopter of laser technology, which is one of the reasons he was so successful in the experimental work he did," says Stuart A. Rice of the University of Chicago. "He was one of the principal experimental spectroscopists who studied molecular crystals with high resolution. And I and my colleagues were interested in the theory, so we had a natural overlap of interests [with Hochstrasser]. We made some predictions separately, and Robin did experiments that verified them."

But Hochstrasser's adoption of lasers for chemical research did far more than confirm theory: It literally shifted the entire experimental paradigm of physical chemistry. Berkeley chemistry professor Charles B. Harris observes, "When I started in chemistry, physical chemistry around the country, especially at Berkeley, was studies of molecules in the gas phase. But from that time in the 1970s until now, there's been an enormous transition from work in the gas phase to work in the condensed phase. And that's been a huge transformation. You hardly have people working in the gas phase anymore. What used to be the numbers of people working in the gas phase in the 1970s are now the numbers of people working in the condensed phase, in a wide variety of areas."

Harris credits Hochstrasser as a major impetus in this shift of emphasis to condensed-matter studies. "Robin is, in my view, one of the principal architects of that transition, along with his students who've gone on to follow up on his work. Robin was the leader in the spectroscopy of the condensed phase in many ways. He innovated some of the most important techniques that are used to this day."

Those techniques quickly found application not just in chemistry and physics but in biology, particularly Hochstrasser's perfection of time-resolved spectroscopy. Using multiple laser beams, such methods can reveal the unfolding of molecular biological processes in real time as they happen. One of Hochstrasser's first graduate students at the University of Pennsylvania, an M.D./Ph.D. student named William A. Eaton, helped to inspire him in applying his spectroscopic techniques to questions of biology and medicine.

"I was his first graduate student who worked in the biological area," says Eaton, who is now Chief of the Laboratory of Chemical Physics at the National Institutes of Health. "Even though he called it biology, it was what everybody else calls biophysics or biophysical chemistry. My thesis had to do with protein crystals, and at that time he was heavily involved in looking at the electronic structure of molecules in crystals, where the crystals were put in high magnetic or electric fields. And he became quite curious about the behavior of protein crystals."

Applying that curiosity in this fresh scientific realm, Hochstrasser developed methods that allowed the direct observation of protein molecules interacting with drugs designed to treat AIDS, Alzheimer's disease, and various influenza strains. "He showed that you could do the same kind of very rigorous molecular spectroscopy on large biological molecules that you could do on the small molecules that occupy the time of most chemical physicists," Eaton explains.

Hochstrasser's techniques made it possible to work at the unprecedented time scale of the femtosecond (a trillionth of a second), opening an entirely new window to molecular biological processes that were previously invisible to researchers. Such work led to the development in the 1990s of what many regard as his crowning achievement, two-dimensional infrared laser spectroscopy. "That has become a big field now in itself," Eaton says. "The reason is that you can get structural information at unprecedented time resolution. There's no other technique where you can watch a system change in time with this kind of time resolution." Stuart Rice agrees: "The major thing he'll be remembered for is the participation and development of 2D spectroscopy."

But Hochstrasser's contributions range far beyond his own work to encompass the thousands of scientists he taught, collaborated with, influenced, and inspired. "His students have gone on to carry on his work," says Charles Harris. Perhaps the most famous is his former student Ahmed Zewail, now a professor at the California Institute of Technology and a 1999 Nobel Laureate, who notes, "Robin was a great mentor to me and to many other graduate students. He was an extraordinary scientist as evidenced by the depth and breadth of his contributions to the lexicon of knowledge. The world has lost a first-rate spectroscopist and physical chemist whose work laid the foundation for some of today's leading advances in ultrafast science."

After such an illustrious career, most scientists would be perfectly happy to slow down and take it easy, but again, Robin Hochstrasser wasn't like most scientists. "Very few scientists kept on producing at the rate that Robin did," says William Eaton. "If you look at his citation record, it's rare because it was increasing." Even just before the time of his passing at age 82, "he was working very hard on new ideas and thinking about new things."

Hochstrasser's contributions extended beyond the merely scientific. "Robin was very dedicated to having science open around the world, and he spent considerable effort in trying to get scientists out of the Soviet Union and other Eastern bloc countries before the wall came down, before the fall of the Soviet Union," remembers Charles Harris. "I was involved with some of that, so I know firsthand what he tried to do. He was quiet about it, he never talked much about it, but he made a significant contribution."

Even with his many important and lasting scientific contributions, his friends and colleagues remember him for more. Eaton recalls, "He did everything with gusto. Everything he did, he did with a passion, whether it was playing tennis or watching a football game between the Glasgow Celtic and the Tottenham Hotspurs. I don't think there was ever a boring moment with Robin Hochstrasser." 

Even the many researchers who never knew him personally but who continue to use the techniques he developed and build upon the discoveries he made possible in chemistry, physics, and biomedicine will agree with Charles Harris's summation of Robin Hochstrasser: "He's a giant."