Geometric description and electronic properties of the principal photosynthetic pigments of higher plants: a DFT study

Abstract

The geometric parameters, local and global chemical reactivity parameters (such as the ionization potential, electron affinity, electronegativity, hardness, softness, chemical potential, and electrophilicity index), as well as the energy levels (HOMO/LUMO) and HOMO-LUMO energy gaps have been determined for the principal carotenoids in higher plants. DFT calculations performed using the B3LYP functional in combination with the 6-31G(d,p) (for geometric parameters) and 6-31 + G(d,p) (for energy parameters) basis sets were carried out to study these structures. The HOMO-LUMO energy gaps obtained with the TPSSh functional were compared with the corresponding energy gaps obtained with B3LYP (when both functionals were used with the 6-31 + G(d,p) basis set). Upon analyzing all of the calculated parameters of the studied molecules, both carotenes were found to be the most reactive, followed by β-cryptoxanthin, zeaxanthin, lutein, violaxanthin, and finally neoxanthin, the least reactive molecule. The results reveal that all of the carotenoids show very high coplanarity in the photochemically active region, resulting in small HOMO-LUMO energy gaps. The calculated local and global chemical reactivity parameters indicate that all of the studied molecules may be classified as soft, as they are good electron donors/acceptors, making these molecules good candidates for use in artificial photosynthetic systems.

Electronic Structure of Carotenoids in Natural and Artificial Photosynthesis

“…In fact, a lower energy for LUMO is associated with a higher electronic affinity. These effects were explained in more detail in our published work [28] and can be studied by further reading Table 1 as shown ahead in this section.…”

Photosynthetic Pigments with Potential for a Photosynthetic Antenna: A DFT Analysis

“…Calculations were done in the Gaussian 09 software suite [14] using DFT [15] in ground-state computations and TD-DFT [16] for excited states. DFT is a robust level of theory to study molecules in their ground state, while TD-DFT is a widely used methodology to compute excited states, including those related to carotenoids and sensitizers for solar cells [13,17].…”

“…Regardless of the good performance of B3LYP hybrid functional in assessing a variety of properties such as molecular adsorption in cluster models of zeolite [20] or geometry and electronic properties of carotenoids [13], other hybrid functionals such as B3P86 should be tested. This functional has been less reported in literature, particularly in evaluating geometry and electronic properties of photosynthetic pigments.…”

“…Before evaluating the theoretical FRET efficiency of an artificial antenna (during subsequent computations not presented in this work), there must be a selection of the pigments that will be employed later, which is one of the aims of the present work. Previously, chemical reactivity indexes derived from conceptual CRDFT have been used, as well as energies (H-L, I, and A), to correlate them with the theoretical efficiency of a dye-sensitized solar cell which uses these kinds of dyes [12] and to assess theoretically carotenoids as potential candidates for a solar energyharvesting device [13]. The general objective of the current research is to find photosynthetic pigments capable of participating in a zeolite-dye system.…”

“…In connection with ω, it measures the ability of a molecule for getting saturated with electrons in maximum flux conditions [38]. Despite the fact that some authors have previously suggested that its value should be as low as possible, in order to improve the performance of theoretically assessed solar cells and artificial devices [12,13], our work and results suggest that desirable values for this property must be as high as possible, since it is conceived by its originators like a kind of power, and appropriate power values are usually needed to be as high as possible. Besides, in preliminary calculations ω of one of the most used synthetic dyes inside zeolite…”