Molecular Origins of Optoelectronic Properties in Coumarins 343, 314T, 445, and 522B

The relationships between the structure and laser dye properties of four coumarin derivatives are investigated to assist in knowledge-based molecular design of coumarins for various optoelectronic applications. Four new crystal structures of coumarins 343, 314T, 445, and 522B are determined at 120 K and analyzed via the empirical harmonic–oscillator–stabilization–energy and bond-length–alternation models, based on resonance theory. Results from these analyses are used to rationalize the optoelectronic properties of these coumarins, such as their UV–vis peak absorption wavelength, molar extinction coefficient, and fluorescence quantum efficiency. The specific molecular structural features of these four coumarins and the effects on their optoelectronic properties are further examined via a comparison with other similar coumarin derivatives, including coumarins 314, 500, and 522. These findings are corroborated by density functional theory (DFT) and time-dependent DFT calculations. The structure–property correlations revealed herein provide a foundation for the molecular engineering of coumarins with “dial-up” optoelectronic properties to suit a given device application.