Structure-Photochemical Function Relationships in Nitrogen-Containing Heterocyclic Aromatic Photobases Derived from Quinoline.

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. 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. 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 → S vertical excitation energy into the visible region while still maintaining a p > 14. Overall, the structure-function relationships developed in this study provide new insights to guide the development of new photocatalysts that employ photobasicity.