1. Influence of Halogen Substituents on the Photophysical Properties of 7-Hydroxycoumarin: Insights from Experimental and Theoretical Studies.
- Author
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Hawkins, BA, Adair, L, Ryder, W, Du, J, Najib, E, New, E, Gale, P, Platts, J, Groundwater, P, Hibbs, D, Hawkins, BA, Adair, L, Ryder, W, Du, J, Najib, E, New, E, Gale, P, Platts, J, Groundwater, P, and Hibbs, D more...
- Abstract
Benzopyrone is a popular fluorescent scaffold, but how chemical modifications affect its properties is less understood. We investigated this using halogenated 7-hydroxycoumarin, unsubstituted 4-methylumbiliferone, and ortho-chloro and bromo substitutions on the phenolic ring. Experimental charge density data and computational methods revealed that halogenation at the ortho position significantly reduced quantum yield (QY). Specifically, 7-hydroxycoumarin (1) had a QY of 70%, while ortho-chloro (2) and ortho-bromo (3) had QYs of 61% and 30%, respectively. Experimental data showed that all probes excited similarly, but the electrostatic potential and dipole moments indicated that 2 and 3 dissipated excitation energy more easily due to charge separation. The heavy-atom effect of Cl and Br did not fully explain the QY reductions, suggesting other radiative decay processes were involved. By incorporating spin-orbit coupling (SOC) effects, we estimated intersystem crossing (ISC) and phosphorescence rates, providing theoretical QYs of 78% for 1, 59% for 2, and 15% for 3. The large deviation for 3 was attributed to its higher SOC potential. Our findings indicate that 3's reduced QY results from a mix of SOC-induced ISC and charge dissipation, while 2's reduction is primarily due to charge separation. Further studies are needed to validate this approach with other scaffolds. more...
- Published
- 2024