Computational Insights into Alizarin’s Suitability for Advanced Solar Energy Technologies

Understanding the photophysical properties of molecular dyes is essential for exploring their potential applications in solar energy conversion and storage. In this work, we investigate the excited-state behavior of alizarin and its potential applications in dyesensitized solar cells (DSSCs) and molecular solar thermal (MOST) systems. Using TD-DFT, MS-CASPT2, and MR-SF-TD-DFT calculations, we characterize its absorption and emission spectra and explore the ground-and excited-state potential energy surfaces. The calculated absorption spectrum shows good agreement with experimental data, while the emission is attributed to a conformer formed through excited-state intramolecular hydrogen transfer. The exploration of the potential energy surfaces reveals possible nonradiative relaxation pathways—specifically through the location of conical intersections—providing insight into the excitedstate deactivation mechanisms of alizarin. Furthermore, the identification of higher-energy conformers separated by substantial energy barriers suggests possible pathways for molecular energy storage. These results provide insight into the photophysical behavior of alizarin and its potential for solar energy applications.