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Movers And Shakers

Tehshik P. Yoon wields light to open new possibilities for organic synthesis

This year’s Trailblazers guest editor also advocates for LGBTQ+ inclusion in chemistry

by Katherine Bourzac
April 8, 2022 | A version of this story appeared in Volume 100, Issue 12


A photo of Tehshik Yoon.
Credit: Lidia Sharapova
Tehshik Yoon

Tehshik P. Yoon is fascinated by photochemistry. He investigates how the energy-packed punch that photons deliver can open new realms of organic reactions. The University of Wisconsin–Madison professor specializes in developing photochemical techniques that drive a reaction to produce a desired molecule.


Hometown: Blacksburg, Virginia

Education: AB, Harvard University, 1996; MS, 1998, and PhD, 2002, California Institute of Technology

Current position: Professor, University of Wisconsin–Madison

LGBTQ+ identity: Gay man

Role model: Among my favorite moments as a new faculty member was getting to thank Carolyn Bertozzi during her seminar visit to Wisconsin. I can’t overstate how eye opening it was for an impressionable graduate student to see an unapologetically out, gay academic achieving at the highest level in our field.

Best professional advice you’ve received: The consistent message I’ve gotten from every mentor I’ve had is that no matter how successful your research might be, the real impact of an academic’s career is measured in the people you get to work with.

Go-to stress reliever: Classical music remains my emotional center. How amazing that the internet gives us immediate access to live performances by masters like Jessye Norman and Itzhak Perlman at their best.

This type of photochemistry has become a popular area of research over the past decade, according to David MacMillan, an organic chemist at Princeton University. “It’s now used all over medicinal chemistry, agrochemistry, everywhere.” And, he says, “it’s all germinating from the early studies that Tehshik did.”

Yoon, the guest editor of C&EN’s LGBTQ+ Trailblazers special issue, says his identity as a gay man is an integral part of his scientific success. “I could probably draw a straight line from the self-preservation mechanisms I put in place as a queer youngster all the way to where I am now,” he says. Stories like his highlight the fact that identity is not incidental to a chemist’s scientific work, he says. For him, it is central.

Yoon knew he was gay from a young age. It wasn’t easy for a gay kid growing up in the 1980s in Blacksburg, Virginia. Media representations of LGBTQ+ people were mostly negative, particularly once the AIDS epidemic took hold. Media coverage of the disease—which was initially called gay-related immune deficiency—perpetuated stereotypes about gay men and blamed them for their own deaths. Discrimination was rampant, with no legal protections to keep people from losing their jobs, housing, or medical care because of being gay.

Tehshik Yoon with his husband, Michael Velliquette.
Credit: Courtesy of Tehshik Yoon
Tehshik P. Yoon (left) with his husband, Michael Velliquette

“At that impressionable age, I internalized the message that this was something to be ashamed of; this is something you can’t talk about,” he says. “This is something that if you are open about it, it will impact your career.”

But he could see a place for himself in the arts. “The arts were a safe space for the outcasts,” he recalls. He played violin, oboe, flute, “everything I could get my hands on,” he says. “I had never heard of a queer scientist before. But I could see what my life could be like in the arts.”

When he went to Harvard University in 1992, his parents told him he could major in whatever he wanted—as long as he completed premed requirements.

Much to Yoon’s surprise, he fell in love with organic chemistry. “There’s a creativity to it. I found all the things in organic chemistry that I had been seeking in music and the arts,” he says. “The idea that you would be the very first person to try something, to make something that never existed before, I found that wonderfully stimulating.”

Yoon continued to pursue his interest in music, too, and sang in the Harvard Glee Club. “We made beautiful music, but you know, it was pretentious,” says Jake Yeston, who went to college with Yoon and is now editor of physical science research at Science. “We wore tailcoats and white bow ties like we were still living in the 1920s. Tehshik thrived a little on the pretentious aspect, and he had this dry, sharp sense of humor.”

Science seemed to bring out a different side of Yoon. “When it came to chemistry, Tehshik was always thoughtful and generous and curious. It was so refreshing,” Yeston says.

To this day, Yeston says, “he is the most successful person I can think of who is really interested in a rising tide that lifts all boats. He is interested in being supportive to everyone around him.”

Tehshik Yoon with the Harvard Glee Club
Credit: Courtesy of Tehshik Yoon
Tehshik P. Yoon (back row, third from left) singing with the Harvard Glee Club

Yoon’s first exposure to photochemistry was at the California Institute of Technology, where he was a graduate student working in the lab of Erick Carreira. Yoon was working on a complex synthesis of a molecule with a very long name (welwitindolinone A isonitrile). The synthesis included a photochemistry step. He put a yellow solution in a photoreactor chamber and turned on the light for 20 min, and the mixture turned clear. “The only reagent was light. I thought that was so cool. There’s no workup. There’s nothing to throw away,” Yoon says. That efficiency and lack of waste is why chemists like Yoon are drawn to the power of photochemistry.

When Carreira moved his lab to Switzerland, Yoon left Caltech with a master’s degree and moved to the University of California, Berkeley, to work on a PhD with MacMillan. Yoon started there in 1999, when MacMillan was a first-year assistant professor.

“If he hadn’t been there, I’m pretty sure my group wouldn’t have made it,” MacMillan says. Yoon drew on his lab experience from his undergraduate years and his master’s work to mentor other students in MacMillan’s lab. “Even though he was a grad student, he would sort of tell people what to do,” MacMillan says.

Tehshik Yoon playing the violin.
Credit: Courtesy of Tehshik Yoon
Tehshik P. Yoon playing violin in his high school senior recital

MacMillan shared the 2021 Nobel Prize in Chemistry for the development of asymmetric organocatalysis, a way of nudging reactions to produce a desired enantiomer. MacMillan recalls working with Yoon on an early paper related to this work, in which MacMillan coined the term organocatalysis. Yoon scratched it out every time he reviewed a draft, pointing out that it wasn’t a real word.

“After the prize I got a message from a technical dictionary that organocatalysis is now in the dictionary, so I sent it to him. See, it’s now a real word!” MacMillan says. “Every time we get together we crack up telling that story.”

While Yoon was having great success during his PhD work, he was struggling personally. He believed he had to hide that he was gay. He carried with him the message he’d internalized growing up that it was not possible to be out and have a career in science, or any professional field.

“I keenly remember feeling this incredible psychological strain of holding back part of my identity from anybody I worked with,” he says. “I can’t imagine if I had kept that going for the last 20 years. At some point I would have broken.”

Yoon’s perspective began to shift when he met Carolyn Bertozzi, a prominent chemical biologist and out lesbian who was then at UC Berkeley. “She was the first out queer faculty member I’d ever met. And not just any queer chemist. She’s Carolyn Bertozzi,” he says. Even as a junior faculty member, he says, Bertozzi, now at Stanford University, was a star.

“It’s an eye-opening experience where you meet somebody and you find out that they’re queer and you just realize, ‘Holy shit, anything is possible,’ ” he says. “And you realize, all of these assumptions you’d internalized about what was possible and what was not—they simply weren’t true.” For Yoon, staying in the closet didn’t seem necessary anymore. And soon, he began demonstrating how a gay scientist could be open about his identity and flourish. Yoon went back to Caltech in 2000 when the MacMillan lab relocated, and he completed his PhD there. Then he moved back to Harvard for a postdoc. In 2005, he started his own lab at the University of Wisconsin, where he soon began making major contributions to photochemistry and organocatalysis.

Yoon’s Wisconsin lab understands that light is a powerful tool for chemists. “When a molecule absorbs a photon of light, it gets pumped up to a highly energetic, highly reactive state,” Yoon says. For example, a photon of blue light packs a very useful amount of energy, 75 kcal per mole. “That’s on the same order of magnitude as a carbon-carbon bond—it’s larger than the strain energy of cyclopropane,” Yoon says. But the energy difference between two enantiomers might be only a single kilocalorie per mole, so delicate tuning of reaction conditions is required to get the desired enantiomer. That kind of careful control is what Yoon and his lab have been working on as they apply photochemical techniques to asymmetric catalysis.

“It was thought that you would need different strategies from other areas of asymmetric catalysis to really achieve the same levels of selectivity” with photochemistry, Yoon says. “Several of us have been discovering that asymmetric catalysis of photochemical reactions is possible and, more importantly, that the catalyst designs you would use are not completely different.”

It’s an eye-opening experience where you meet somebody and you find out that they’re queer and you just realize, ‘Holy s---, anything is possible.’ 

Sarah Reisman, a synthetic chemist at Caltech, says one of Yoon’s major contributions to the field is the development of techniques and photocatalysts that can drive reactions with visible, rather than ultraviolet, light (J. Am. Chem. Soc. 2008, DOI: 10.1021/ja805387f). With visible light, chemists can more carefully target particular functional groups, giving greater control over the synthesis of organic molecules. Systems that use visible light should also be easier to scale up for use in industry, Reisman says.

Reisman also admires Yoon’s advocacy work. She says Yoon “thinks really deeply about issues related to diversity, equity, and inclusion” and uses his stature—and substantial Twitter following—to advocate for those issues. She collaborated with Yoon on a 2020 editorial affirming the importance of diversity and inclusion in organic chemistry (ACS Cent. Sci. 2020, DOI: 10.1021/acscentsci.0c01027). It was a response to an infamous essay in the chemistry journal Angewandte Chemie International Edition that criticized efforts to diversify organic chemistry. (The original essay was removed from the journal’s website.)

The editorial in response, which Yoon and Reisman coauthored with Richmond Sarpong and Matthew Sigman, pulls no punches. “At the outset, we find it morally unjustifiable to remain silently complicit with a system that has historically disenfranchised multiple subgroups within our community,” they write. “Working to dismantle structural barriers that have prevented equitable participation of marginalized groups in STEM should be a mandate.”

Students also admire Yoon’s advocacy for diversity, equity, and inclusion. Seeing someone like Yoon, a brilliant, Korean American organic chemist who loves art and fashion and music and invites students to the home he shares with his husband, “abolishes the sense that any identity is a monolith,” says Stephanie Knezz, now a chemist at Northwestern University. Yoon was on Knezz’s PhD thesis committee.

“He was a prevalent force in my development, in figuring out what a professional chemist is,” she says. “Tehshik exemplified queer excellence.” Knezz, who is pansexual, sees a ripple effect from Bertozzi to Yoon to herself.

“I feel a strong obligation to try to support and mentor queer students,” Yoon says. It’s a way of paying forward what Bertozzi’s presence at Berkeley meant for him. He says it also brings him great joy. Talking to 20-year-olds, he says, helps him appreciate how quickly things have gotten better for LGBTQ+ people during his lifetime. Yoon points to legal victories such as the Supreme Court’s 2015 decision to uphold marriage equality and the fact that mainstream movies and TV shows now feature positive queer and transgender characters played by queer and trans actors.

But the fight is far from over, Yoon says. The scant data on representation in academia suggest that STEM fields have an LGBTQ+ retention problem on the same scale as that for women and for underrepresented racial and ethnic groups, Yoon says. LGBTQ+ people still face discrimination and marginalization in the larger society, and recent legislation targets children in particular. “State governments are trying to prevent us from talking about queer people in schools,” he says, referring to a recent education law in Florida. And in February, Texas governor Greg Abbott directed state agencies to designate gender-affirming care for transgender and nonbinary children (which is upheld by medical and mental health organizations) as a form of child abuse. These are just two recent examples that have made the national news. According to the American Civil Liberties Union, 147 anti-trans laws were debated in state legislatures in 2021; the organization is tracking 280 such laws already in 2022.


“There are real consequences for the lives, the safety, the employment of queer people right now,” Yoon says. “How can you think that this is not an important issue for scientists right now? I think as human beings, we have to have these discussions.”

Also, for many people, Yoon included, identity is interwoven with their scientific success. He says a great part of his photochemical intuition comes from the musical sense he developed as a young gay man drawn to the arts.

“We talk about wave functions, we talk about resonance, and those are all concepts that make sense to a musician,” he says. “I draw on all of my background in the work I do on a daily basis.”


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