Density Functional Theory for Charge Transfer:  The Nature of the N-Bands of Porphyrins and Chlorophylls Revealed through CAM-B3LYP, CASPT2, and SAC-CI Calculations

Abstract

While density functional theory (DFT) has been proven to be extremely useful for the prediction of thermodynamic and spectroscopic properties of molecules, to date most functionals used in common implementations of DFT display a systematic failure to predict the properties of charge-transfer processes. While this is explicitly manifest in Rydberg transitions of atoms and molecules and in molecular charge-transfer spectroscopy, it also becomes critical for systems containing extended conjugation such as polyenes and other conducting polymers, porphyrins, chlorophylls, etc. A new density functional, a Coulomb-attenuated hybrid exchange-correlation functional (CAM-B3LYP), has recently been developed specifically to overcome these limitations, and it has been shown to properly predict molecular charge-transfer spectra. Here, we demonstrate that it predicts qualitatively reasonable spectra for porphyrin, some oligoporphyrins, and chlorophyll. However, alternate density functionals developed to overcome the same limitations such as current-density functional theory are shown, in their present implementation, to remain inadequate. The CAM-B3LYP results are shown to be in excellent agreement with complete-active-space plus second-order Møller-Plesset perturbation theory and symmetry-adapted cluster configuration interaction calculations: These depict the N and higher bands of porphyrins and chlorophylls as being charge-transfer bands associated with localization of molecular orbitals on individual pyrrole rings. The validity of the basic Gouterman model for the spectra of porphyrins and chlorophylls is confirmed, rejecting modern suggestions that non-Gouterman transitions lie close in energy to the Q-bands of chlorophylls. As porphyrins and chlorophylls provide useful paradigms for problems involving extended conjugation, the results obtained suggest that many significant areas of nanotechnology and biotechnology may now be realistically treated by cost-effective density-functional-based computational methods.

Turbo charging time-dependent density-functional theory with Lanczos chains

“…In the last few years there have been several calculations of its low energy spectrum relying on different ab initio techniques. [57][58][59][60][61][62] Despite the fact that TDDFT seems to produce spurious charge transfer states in the visible region, 60 according to our calculations the overall shape of the low energy part of spectrum seems to be correctly predicted. Our calculations have been performed using a supercell of dimensions 35ϫ 45 ϫ 55a 0 3 with the PW91 XC functional 63 and USPPs.…”

TD-DFT calculations and MCD spectroscopy of porphyrin and phthalocyanine analogues: rational design of photosensitizers for PDT and NIR region sensor applications

“…A similar effect is observed when the frontier π -MOs of naphthalocyanine (9) and anthracocyanine (10) are compared to those of Pc (8), but it is smaller in magnitude since the additional rings lie further from the inner perimeter where the largest MO coefficients are anticipated for the frontier π -MOs derived from the HOMO and LUMO of the parent perimeter ( Figure 3). Benzo substitution has a destabilizing effect on the energy of the a MO because there is an antibonding interaction at the point of attachment of the C 4 H 4 bridges that are added upon fused-ring-expansion and there are also nodal planes on the 4 aza-nitrogens and hence a smaller stabilization effect due to the electronegativity (1), and its analogues fused-ring-expanded at the pyrrole β -carbons with benzene (2), 2,3-naphthalene (3), anthracene (4), phenanthrene (5), and phenanthroline (6) moieties, and the corresponding tetraazaporphyrins (7-12), β , β -tetrapyrazino-substituted tetraazaporphyrin (13), and its analogues fused-ring-expanded with benzene (14), 2,3-naphthalene (15), phenanthrene (16), and phenanthroline (17) moieties, and the corresponding β , β -tetrabenzopyrazino-substituted structures (18)(19)(20)(21)(22). Bolder black lines are used to highlight the 4 frontier π -MOs that are associated with Michl's perimeter model.…”

Push–pull type manganese(III)corroles: Synthesis, electronic structures and tunable interactions with ctDNA

“…TDDFT calculations were carried out in a similar manner with the CAMB3LYP functional, since its longrange correction is known to provide more accurate predictions in the context of porphyrinoids with closed shell electronic configurations for the energies of transitions with significant charge transfer character [27,28].…”