Optical absorption and electronic spectra of chlorophylls a and b

Abstract

a Photosynthesis includes capturing sunlight by an assembly of molecules, called chlorophylls, and directing the harvested energy in the form of electronic excitations to the reaction center. Here we report, using realspace density functional theory and time-dependent density functional theory together with GW calculations, the optical and electronic properties of the two main chlorophylls in green plants, namely, chlorophylls a and b. Furthermore, we estimate the dipole and primitive quadrupole electric moments of these molecules. We employ Casida's assignment ansatz to study the absorption spectra of the chlorophylls in the two main red and blue regions at various environments with different exchangecorrelation functionals. In addition, we obtain the band gap of chlorophylls a and b, which are all in remarkable agreement with experimental observations.

Relaxation Dynamics of Chlorophyll b in the Sub-ps Ultrafast Timescale Measured by 2D Electronic Spectroscopy

“…respectively. In agreement with previous investigations, the lowest energy band at 650 nm (15,390 cm −1 ) is assigned to Qy(0,0) transition, while higher energy signals are attributed to the mixing of Qy(0,n) and Qx states [17,22,23]. As expected [24], the spectrum at 77 K is slightly blue, shifted with respect to the one at RT, and is characterized by narrower bandwidths.…”

“…According to this model, the lowest energy transitions are labeled as Q-bands. They are the result of two partially overlapping electronic transitions identified as Q x (S 0 → S 2 ) and Q y (S 0 → S 1 ), with x and y indicating the polarization directions within the macrocycle plane [22]. At RT, these bands are broadened by inhomogeneous effects and by the activation of low-frequency molecular vibrations.…”

Vibronic structure of photosynthetic pigments probed by polarized two-dimensional electronic spectroscopy andab initiocalculations

“…For both molecules the phytyl-containing side groups were removed to reduce computational costs, since they have no impact on spectral properties. 61,96,97 Either zero, one, or two solvent molecules were added explicitly, giving rise to an unligated (tetra-), monoaxially ligated (penta-), or biaxially ligated (hexa-coordinated) central Mg ion, respectively. 98,99 The split-valence double-zeta basis set 6-31++G(d,p) 100 was used for all calculations.…”

Physicochemical, antioxidant properties of carotenoids and its optoelectronic and interaction studies with chlorophyll pigments

“…2 a). For Chla and Chlb, the ionization potentials are determined to be 4.19 eV and 4.45 eV in the PBE/DPZ level; however, it is obtained 4.96 and 5.22 by using the Octopus code, as well as 4.79 and 5.17 by applying the B3LYP/6-31G* hybrid functionals, The dipole moment of Chla (4.79 D) is larger than that of Chlb (1.36 D) 43 . Carotenoids are well-known antioxidants and they have the ability to quench singlet oxygen and scavenge toxic free radicals preventing or reducing damage to living cells.…”