A quantum-chemical study of the chlorophyll phosphorescence spectrum: Electron-vibrational coupling and coordination effects

Abstract

The lowest triplet state and phosphorescence spectra of tetra-, penta- and hexacoordinated chlorophylls a, b and d were investigated by density functional theory and multimode harmonic approximation. We find good agreement between computed and experimental energies of the triplet state. Vibrational modes sensitive to coordination were identified. The simulated and experimental spectra are in reasonably good agreement. Comparing high-resolution simulated fluorescence and phosphorescence spectra we support an observation of Hartzler et al. (2014) [14] that the same vibrational modes govern lineshapes of phosphorescence and fluorescence spectra, although with different coupling strengths.