Modernizing a Photochemistry Course

Chemistry professor Michael Therien Guest Post by Dr. Michael J. Therien, William R. Kenan, Jr. Professor of Chemistry, and recipient of a Jump Start Grant from Learning Innovation.

I have been teaching a course in photochemistry and photophysics (Chem 590) for many years, a class primarily designed for advanced undergraduates and first- and second-year graduate students whose research interests significantly involve physical chemistry (PCHEM). From this class, students are supposed to learn a variety of fundamentally important concepts in PCHEM, such as electronic, vibrational, and spin configurations of electronically excited states, radiative and nonradiative transitions between states, and inter-molecular energy transfer reactions. Such subjects may sound very unfamiliar to most people; in fact, they are also some of the most abstract and difficult concepts for students in the chemistry major, despite their importance for understanding light-related phenomena in modern chemistry research and in technologies that impact society.

For this class, textbooks with titles similar to “principles of photochemistry”, or “an introduction to photochemistry” are typically used; these books present key concepts in the language of quantum mechanics. Indeed, for many years, I have used such textbooks as a roadmap for the photochemistry class, simply because they are both comprehensive and accurate. However, at a more practical level, these standard text fail many students, as much of the knowledge conveyed is difficult to connect to modern research problems in photochemisty and photophysics. Another key problem is that many of the so-called standard textbooks for this subject emphasize research issues that were important more than thirty years ago.

Within this context, I have been thinking about modernizing this class to make better connections between course content and the students’ their own research activities at Duke. With the help of Dr. Yusong Bai, a postdoctoral fellow in my laboratory, Chem 590 has been updated – not only in terms of course content, but also in the way in which it is taught.

1. Teaching traditional photochemical knowledge with cutting-edge research examples.
On one hand, we updated my earlier lecture presentations by inserting new research examples tied closely to important concepts, and cut out unnecessary detailed material. Based on the core contents of each lecture, we screened research work published during the recent decade and incorporated examples of research problems not only closely related to lecture contents, but also those that matched student research interests and background. In this manner, we hoped to establish solid connections between the unfamiliar PCHEM concepts and modern research activities in the discipline.

On the other hand, we added entirely new lectures based on forefront research topics. For example, following lectures on light-induced transitions between states, and energy and electron transfer reactions in inorganic/organic molecules, multiple lectures on topics important for modern solar energy conversion technologies (e.g. exciton diffusion, organic photovoltaics and dye-sensitized solar cells) were presented, wherein fundamental knowledge taught in previous lectures was extensively exploited. We aimed to both reinforce student understanding of fundamental concepts, and make connections to modern research problems.

2. Building up hands-on learning modules
The most effective way of reinforcing new concepts is through hands-on experience. Chem 590 introduces many ideas that have their foundation in quantum mechanics, which can be quite difficult to understand in a lecture-only course format. In this regard, Yusong and I designed and incorporated four in-class experiments; these involved: (i) measuring absorption, emission and excitation spectra for organic molecules, (ii) determining fluorescence quantum yields of organic molecules in solution, (iii) measuring the fluorescence lifetimes of inorganic complexes, and (iv) acquiring nanosecond time domain pump-probe transient absorption spectra, which provide insights into how the properties of molecules are altered after they absorb light. All of these laboratory activities involved direct “hands-on” student use of many state-of-the-art spectroscopic instruments. These experiments helped the students translate abstract lecture concepts within a laboratory setting. For example, lectures were presented on “radiative transitions” and “nonradiative transitions” between states in molecules, but how are these processes made evident through real-world observations? To enhance student understanding, students actually measured a “fluorescence quantum yield”, a parameter that quantifies the efficiency of the “radiative transition” process, and a “fluorescence lifetime”, a dynamic parameter that reflects how fast a “radiative or nonradiative process” occurs in a given molecule. Furthermore, the experiments we incorporated in the class involved key techniques that are commonly used in the field of photophysics and photochemistry. As such, the students not only characterized real-world phenomena relevant to the course, but also acquired practical skills that may impact their own future research – the ultimate goal of this class.