Illuminating the Science of Light and Molecules
1945-2019
On July 16, 2019, the scientific community lost a brilliant mind whose work had literally helped illuminate the molecular world. Enrique San Román (1945–2019) was not just a scientist; he was an architect of understanding, a researcher who dedicated his life to unraveling how light interacts with matter at the most fundamental level. As an Argentinian photochemist, San Román left behind a legacy of discovery that continues to influence how we understand everything from biological processes to new materials development.
"A meticulous and very knowledgeable scientist and teacher, a loyal friend and a generous and integer human being" 2
For over three decades, San Román led the Photochemistry and Chemical Kinetics research group at the University of Buenos Aires, where he mentored generations of scientists and produced a body of work that would earn him international recognition 1 .
To appreciate San Román's contributions, we must first understand the basics of photochemistry—the study of chemical reactions that are initiated by light. When molecules absorb light energy, they enter an excited state that makes them more reactive than they would normally be.
Events between light absorption and chemical reaction including fluorescence, energy transfer, and intersystem crossing.
Photosynthesis in plants, solar cell technology, and digital displays all rely on photochemical principles.
Throughout his career, San Román maintained a particular fascination with dye molecules—highly colored compounds that can absorb and emit light efficiently. His research encompassed several key areas:
How energy moves from one molecule to another
How molecules change shape when exposed to light
How and why molecules stop emitting light
How molecules transition to longer-lived excited states
One of San Román's significant contributions was his work on symmetrical carbocyanines—a class of dye molecules used in various technologies. In 1994, he and his colleagues published a landmark study examining how temperature and viscosity affect fluorescence and photoisomerization in these molecules 1 .
One of San Román's most compelling lines of research emerged in his later career—the investigation of what happens to dye molecules at extremely high concentrations.
In a 2018 study published in Photochemistry and Photobiology, San Román and his collaborators designed an elegant experiment to answer this question 1 . They focused on xanthene dyes at high concentrations in solid environments.
The team's findings challenged conventional wisdom about how dyes behave at high concentrations. Instead of simply quenching each other's fluorescence, the densely packed dye molecules were engaging in charge transfer interactions that led to the formation of triplet states.
| Observation | Traditional Expectation | San Román's Finding |
|---|---|---|
| Fluorescence intensity | Decreases with concentration | Decreases more rapidly than predicted |
| Triplet formation | Minimal at high concentration | Significant increase due to charge transfer |
| Quantum yield | Should remain constant | Changes with concentration |
| Response to UV radiation | Similar to dilute solutions | Enhanced sensitivity |
This was significant because triplet states have longer lifetimes than typical excited states and can participate in different chemical reactions. The discovery had implications for understanding photodegradation and for designing better organic LEDs and other optoelectronic devices.
San Román's research relied on both specialized equipment and carefully designed experimental materials.
| Reagent/Material | Function in Research | Key Studies |
|---|---|---|
| Xanthene dyes (fluorescein, rhodamine) | Model compounds for studying photophysics at high concentrations | Photophysics of Xanthene Dyes at High Concentrations (2018) |
| Symmetrical carbocyanines | Investigating photoisomerization and viscosity effects | Temperature-dependence of fluorescence (1994) |
| Fluorosulfate radicals | Studying recombination kinetics using flash photolysis | Cinética de la recombinación de radicales fluorosulfato (1982) |
| Chlorotrifluoride | Examining photochemical formation kinetics | Die Kinetik der Photochemischen Bildung von Chlortrifluorid (1970) |
| Light-scattering powder samples | Testing methods for measuring triplet quantum yields | Triplet quantum yields measured by LIOAS (2012) |
Beyond his experimental work, San Román made significant contributions to the theoretical framework of photochemistry. He played a key role in developing and standardizing methods for measuring photoluminescence quantum yield.
As co-coordinator of this project, San Román helped establish international standards that allowed researchers around the world to compare their results reliably 1 .
Enrique San Román's influence extended far beyond his specific research findings. As the leader of the Photochemistry and Chemical Kinetics research group at the University of Buenos Aires from 1984 until his death, he shaped the minds and careers of countless students and colleagues 2 .
Generations of scientists trained under his guidance
Known for generosity with time and ideas
| Field | Application of Research | Specific Contribution |
|---|---|---|
| Materials Science | Organic solar cell development | Understanding energy transfer at high dye concentrations |
| Biomedical Imaging | Fluorescent tags and sensors | Establishing standards for fluorescence measurements |
| Environmental Science | UV radiation impact assessment | Studying dye response to ultraviolet light |
| Analytical Chemistry | Chemical detection methods | Flash photolysis techniques for radical study |
| Education | Photochemistry curriculum | Mentoring students and developing standardized methods |
The international recognition of his work was evident in the session dedicated to his memory during the Encounter of Latin-American Photochemists (ELAFOT) held in Viña del Mar, Chile, in November 2019—just months after his passing 1 .
Enrique San Román's career demonstrates how curiosity-driven research into fundamental phenomena can yield insights with broad practical applications. His work to understand what happens when molecules absorb light—especially when they're packed together in unusual ways—has provided scientists with both theoretical frameworks and practical tools for advancing technology.
Perhaps more importantly, San Román exemplified the collaborative, generous spirit that drives science forward. His contributions to standardization and education ensured that his impact would multiply through the work of others. As we continue to develop technologies that harness light—from more efficient solar energy conversion to better medical diagnostics—we build upon the foundation that researchers like Enrique San Román have established.
In the end, San Román's story reminds us that science is both a personal and collective endeavor. The light he studied so meticulously becomes a fitting metaphor for his own career: just as excited molecules transfer their energy to neighbors, so too did San Román energize and illuminate the minds around him, creating chains of inspiration and discovery that will continue long after his passing.
Explore how dye concentration affects fluorescence:
Adjust the slider to see how increasing concentration affects photophysical processes based on San Román's findings.