In this work, we present a theoretical study at the density functional theory (DFT) level and time-dependent DFT of the ground and singlet excited states of electron donor–acceptor complexes formed by porphyrin (TPP)/smaragdyrin (TPOS) (expanded porphyrin), as light-harvesting systems, and fullerene (C60)/graphene oxide (GO), as acceptor nanocarbon structure. We investigate the effect of the nanocarbon on UV–vis electronic absorption of porphyrin/smaragdyrin, using the functionals B3LYP, PBE, M06, and wB97XD. The results showed the lowest deviation of the Q-band for the functional M06 (0.01–0.02 eV). Electronic absorption spectra calculated for the complexes with M06 predict that (a) graphene oxide increases the intensity of the Soret band, (b) fullerene produces a red-shift of the Q bands (4 nm) with respect to graphene oxide, and (c) smaragdyrin causes a red-shift of Q (27–48 nm) and Soret (37 nm) absorption bands as compared to porphyrin. We also investigate the effect of the nanocarbon structure on the charge-transfer (CT) excited states. Using the perturbative delta-SCF method with the PBE functional, we found that the charge-transfer excitation energy increases as TPOS-C60 (2.53 eV) < TPP-GO (2.89 eV) < TPP-C60 (3.01 eV) < TPOS-GO (3.28 eV). The presence of a nanocarbon structure affects more strongly smaragdyrin (∼0.8 eV) than porphyrin (∼0.1 eV). We show that the binding between smaragdyrin and fullerene C60 favors the charge separation states with a lower energy cost, which means that these systems present an advantage for its application in photovoltaic cells.

Dye-sensitized solar cells (DSSC) are presented as an alternative among renewable energies where the dye plays an important role to obtain an effective device. Our goal in this work is to examine the influence of several bridging functional groups between the BODIPY and oxasmaragdyrin systems forming dyads (D), as potential components of DSSC, on the aromatic, photophysical, and charge transport properties. A set of 11 dyads made of the oxasmaragdyrin with 2,6-dimethoxyphenyl and methylamine groups in two of their meso carbons (S) and the 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY, B) moieties that differ in the binding bridge between them has been analyzed with density functional theory (DFT). The geometries were optimized with the B3LYP/6-311G­(d,p) level of theory employing D3 Grimme′s correction, and a set of six functionals (B3LYP, BHandHLYP, CAM-B3LYP, PBE0, wB97X, TPSSh) was evaluated for reference systems in time-dependent DFT calculations. We found that TPSSh presents the best agreement with the available data of UV–vis spectra, so it was used for calculation of the electronic absorption spectra of the 11 oxasmaragdyrins and 11 dyads. When the bridge between S and B consists of one (D3), two (D5), or three acetylene units (D6), a strong absorption band in the infrared region around 1000 nm can be achieved. These bands correspond to charge-separated excited states that favor a panchromatic absorption in that region. The aromaticity index NICS(0) computed at the macrocycle center ring critical point using the GIAO/B3LYP/6-311G­(d,p) level of theory shows in all these systems an aromatic character for the oxasmaragdyrin macrocycle (from −10.7 to −12.4 ppm). We also found that all dyads present a favorable electron injection toward the semiconductor TiO2 because the LUMO energy of the dyad is higher than the conduction band of the semiconductor (−4.3 eV) used in a solar cell. Besides, the HOMO energy of the dyads D3, D5, and D6 is lower than the redox potential (−4.8 eV) of a mediator as the I–/I3 – system used to recover it after circulation of electrons. Nonequilibrium Green′s function-based calculations performed for a couple of dyads, with (D6) and without (D4) a significant charge transfer band, connected to Au electrodes show that D6 was to be a better conductor, in agreement with the charge transfer results obtained from the photophysical properties. Finally, the Gibbs free energy for the formation of the dyads here investigated is calculated. All of them are shown to be exergonic reactions (ΔG solution < 0), which suggests that these systems could be synthesized.

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Porphyrins and expanded porphyrins are fascinating molecular structures, and its wide applicability in different fields of the nanoscience has produced an extensive number of scientific publications. The purpose of this article is to review the research performed on porphyrins and expanded porphyrins in the Latin American region at a theoretical level of quantum chemistry using different methodologies available. The present review is organized considering the most important applications that these molecular systems have found. In this way, we classify the reported works in the following fields studied by the nanoscience: molecular electronics, dye‐sensitized solar cells, and photodynamic therapy. Because of its relevance, we also highlight other reports focused on the topological analysis of the electron density and aromaticity. Current investigation on these topics applied to porphyrin‐ and expanded porphyrin‐based systems and the future perspective in this field are presented.

In the present work, we theoretically investigate the push–pull effect in new dyads of chromophores formed by substituted Zn­(II) porphyrin (P) and squaraine (SQ) that could be potential components of dye-sensitized solar cells (DSSCs). The effect of electron-donating moieties (amine, methoxy, and methyl) bound to porphyrin in meso-position C20 on the optical and charge transport properties of nine dyads (D1–D9) was studied, as well as the formation reaction of these. After a calibration procedure with 13 density functionals, the electronic spectra of the dyads were computed (TPSSh/def2-TZVP) with time-dependent density functional theory (TD-DFT). Dyads with amines (D5–D9) show a push effect denoted by the red-shifting of the Q-bands (up to 727 nm), while dyads with methyl or methoxy substituents (D1–D4) show no significative changes. Charge transfer bands computed with both TD-DFT and perturbative ΔSCF approaches preferably show a P → SQ transition, which indicates that porphyrin is a better electron-donating moiety (push effect), while squaraine is a better electron-withdrawing moiety (pull effect). Charge transport properties of the dyads calculated with the Keldysh nonequilibrium Green’s function (NEGF) formalism show a similar trend, with the current shifting P → SQ more favorably for dyads with amine groups. The latter would be more convenient for DSSCs.