Excited State Frequencies of Chlorophyll f and Chlorophyll a and Evaluation of Displacement through Franck-Condon Progression Calculations.

Noura Zamzam,Jasper Van Thor

doi:10.3390/molecules24071326

Abstract

We present ground and excited state frequency calculations of the recently discovered extremely red-shifted chlorophyll f. We discuss the experimentally available vibrational mode assignments of chlorophyll f and chlorophyll a which are characterised by particularly large downshifts of 131-keto mode in the excited state. The accuracy of excited state frequencies and their displacements are evaluated by the construction of Franck–Condon (FC) and Herzberg–Teller (HT) progressions at the CAM-B3LYP/6-31G(d) level. Results show that while CAM-B3LYP results are improved relative to B3LYP calculations, the displacements and downshifts of high-frequency modes are underestimated still, and that the progressions calculated for low temperature are dominated by low-frequency modes rather than fingerprint modes that are Resonant Raman active.

Highlights

Chlorophylls found in photosynthetic organisms are responsible for light harvesting in the antenna complexes, and the subsequent transfer of excitation energy to photosynthetic reaction centres with almost 100% quantum efficiency
We present the density function theory (DFT) based calculations of vibrational frequencies of chlorophyll a and chlorophyll f in2004 the ground states using the exchange-correlation functional proposed by Yanai et al in which and usedexcited a Coulomb-attenuating two CAM-B3LYP, andtothe
We review the assignments of ground and excited states chlorophyll vibrational modes in experimental spectra of isolated chlorophyll a and reaction centres of photosystem I (PSI) and photosystem II (PSII), with a particular focus on carbonyl bands shown to downshift upon excited state formation

Summary

Introduction

Chlorophylls found in photosynthetic organisms are responsible for light harvesting in the antenna complexes, and the subsequent transfer of excitation energy to photosynthetic reaction centres with almost 100% quantum efficiency. Specific chlorophylls act as electron transfer cofactors and are involved in the initial charge separation processes [1]. The marked difference in the structure of chlorophyll f as compared to that of chlorophyll a is a formyl group replacing the methyl group at the 21 position. This extra carbonyl group in Chl f leads to different vibrational bands in the carbonyl absorption region of the infrared spectrum. We examine the vibrational properties of chlorophyll a and the newly discovered chlorophyll f in the ground and excited states considering experimental and theoretical data

Methods

Results

Conclusion