Computational Studies on Structural and Excited State Properties of Modified Chlorophyll f with Various Axial Ligands

TL;DR

This study uses TDDFT calculations to analyze the excited state properties of modified chlorophyll f with various axial ligands, revealing shifts in absorption bands and insights into electron donation and acceptance behavior.

Contribution

It provides computational evidence on how axial ligands influence the spectral and electronic properties of chlorophyll f derivatives, highlighting the role of specific substituents and ligands.

Findings

Red shift in Qy band due to extended delocalization from -CHO group

Absorption bands shift to higher wavelengths with axial ligands

Chlide f -Imidazole is a good electron donor, Chlide f -CH3COOH is a good electron acceptor

Abstract

Time Dependent Density Functional Theory (TDDFT) calculations have been used to understand the excited state properties of "modified-chlorophyll" f ('Chlide' f), Chlide a, Chlide b and axial ligated (with Imidazole, H2O, CH3OH, CH3COOH, C6H5OH) Chlide f molecules. The computed differences among the Qx, Qy, Bx and By band absorbance wavelengths of Chlide a, b and f molecules are found to be comparable with the experimentally observed shifts for these bands in 'chlorophyll' a ('chl' a), chl b and chl f molecules. Our computations provide an evidence that the red shift in Qy band of chl f is due to the extended delocaliztion of macrocycle chlorin ring due to the presence of -CHO group. The local contribution from the -CHO substituent to the macrocycle chlorin ring stabilizes the corresponding molecular orbitals (LUMO of the Chlide f and LUMO-1 of the Chlide b). All the absorption bands of Chlide f shift to higher wavelengths on the addition of axial ligands. Computed redox potentials show that, among the axial ligated Chlide f molecules, Chlide f -Imidazole acts as a good electron donor and Chlide f -CH3COOH acts as a good electron acceptor.