Undergraduate Research Experience Publications

Our recently published joint experiment-theory study of the photo-oxidative intramolecular cyclization of 2′-alkynylacetophenone oximes, performed in collaboration with the de Lijser group, presented the first reported formation of isoindole N -oxides. That study focused on determining a mechanistic explanation for the unexpected chemistry observed when three 2′-alkynylacetophenone oximes were photo-oxidized with 9,10-dicyanoanthracene (DCA), specifically the derivatives with a phenyl, isopropyl, or n -butyl substituent at the alkynyl group. Here, we use density functional theory to develop a broader understanding of the scope of this chemistry. In particular, we demonstrate that substituents on the alkynyl group and on the central benzene ring can significantly modulate the thermodynamic driving force for oxime radical cation generation when DCA is used as the photosensitizer. In contrast, substituents are shown to have a small impact on the chemical reactivity of the radical cation intermediates. In particular, 5-exo radical cation cyclization, which ultimately results in an isoindole N -oxide product, is always kinetically and sometimes also thermodynamically preferred over 6-endo radical cation cyclization, which would produce an isoquinoline N -oxide product. Overall, this study provides mechanistic insights into the diversity of isoindole N -oxides that can be produced through the photo-oxidative cyclization of 2′-alkynylacetophenone oximes .

Photobases are compounds that become more basic when promoted to an excited electronic state. Previous experimental and computational studies have demonstrated that several quinoline and quinoline-derived compounds are strong photobases (pK _a ^* > 14). Moreover, the strength of photobasicity was shown to depend strongly on the identity and position of the substituent group(s), with the strongest photobases having multiple electron-donating substituents on a fused benzene ring as opposed to the ring containing the photobasic nitrogen atom. These electron-donating substituents build up electron density on one side of the molecule that shifts onto the nitrogen-containing ring in the electronic transition. This shift in electron density produces an increase in negative charge on the ring nitrogen atom responsible for the photobasicity. In this paper, we expand on our previous investigation to study the effect of an additional ring nitrogen atom on photobasicity in aromatic heterocycles. In particular, we consider how the thermodynamic driving force for excited-state protonation can be tuned by changing the relative placement of the ring nitrogen atoms and varying the position and number of electron-donating substituents. In the set of 112 molecules screened, we identified 42 strong photobases with generally comparable pK _a ^* but lower vertical excitation energies than the quinoline derivatives with only a single ring nitrogen atom. We additionally explored photobasicity in substituted azaindole and carboline derivatives, identifying 76 strongly photobasic compounds with pK _a ^* as large as 22.6 out of the 155 compounds that we considered. Overall, this work provides new insights into the design principles necessary to develop next-generation photocatalysts that employ photobasicity.

Active matter systems exhibit rich emergent behavior due to constant injection and dissipation of energy at the level of individual agents. Since these systems are far from equilibrium, their dynamics and energetics cannot be understood using the framework of equilibrium statistical mechanics. Recent developments in stochastic thermodynamics extend classical concepts of work, heat, and energy dissipation to fluctuating non-equilibrium systems. We use recent advances in experiment and theory to study the non-thermal dissipation of individual light-activated self-propelled colloidal particles. We focus on characterizing the transition from thermal to non-thermal fluctuations and show that energy dissipation rates on the order of ∼k _B T s ⁻¹ are measurable from finite time series data.

Photobases are compounds that become strong bases after electronic excitation. Recent experimental studies have highlighted the photobasicity of the 5-R quinoline compounds, demonstrating a strong substituent dependence to the p K _a ^* . In this paper, we describe our systematic study of how the thermodynamic driving force for photobasicity is tuned through substituents in four families of nitrogen-containing heterocyclic aromatics. We show that substituent position and identity both significantly impact the p K _a ^* . We demonstrate that the substituent effects are additive and identify many disubstituted compounds with substantially greater photobasicity than the most photobasic 5-R quinoline compound identified previously. We show that the addition of a second fused benzene ring to quinoline, along with two electron-donating substituents, lowers the S ₀ → S _PBS vertical excitation energy into the visible region while still maintaining a p K _a ^* > 14. Overall, the structure–function relationships developed in this study provide new insights to guide the development of new photocatalysts that employ photobasicity. .