Tuning the Acceptor Unit of Push–Pull Porphyrazines for Dye-Sensitized Solar Cells

Abstract

A family of four push–pull porphyrazines of A3B type, where each unit A contains two peripheral propyl chains and the unit B is endowed with a carboxylic acid, were prepared. The carboxylic acid was attached to the b-position of the pyrrolic unit, either directly (Pz 10), or through cyanovinyl (Pz 11) and phenyl (Pz 7) groups. The fourth Pz (14) consisted in a pyrazinoporphyrazine wherein the dinitrogenated heterocycle provided intrinsic donor–acceptor character to the macrocycle and contained a carboxyphenyl substituent. The direct attachment of the carboxylic acid functions and their linkers to the porphyrazine core produces stronger perturbation on the electronic properties of the macrocycle, with respect to their connection through fused benzene or pyrazine rings in TT112 and 14, respectively. The HOMO and LUMO energies of the Pzs, which were estimated with DFT calculations, show little variation within the series, except upon introduction of the cyanovinyl spacer, which produces a decrease in both frontier orbital energetic levels. This effective interaction of cyanovinyl substitution with the macrocycle is also evidenced in UV/Vis spectroscopy, where a large splitting of the Q-band indicates strong desymmetrization of the Pz. The performance of the four Pzs as photosensitizers in DSSCs were also investigated.

Self-Assembled Monolayers of Push–Pull Chromophores as Active Layers and Their Applications

“…With such a seminal molecule, they obtained a PCE (power conversion efficiency) of 3.42% and opened the way for the improvement in panchromatic light harvesting by properly tuning the peripheral functions. In particular, in a more recent work, the authors studied the effect of tuning of the electron-donor unit of push-pull porphyrazines [87] (Figure 6), showing its effect on both adsorption and electron injection processes, thus highlighting that porphyrazine design is a delicate process with a significant effect on the electronic properties of organic dyes and therefore on DSSC operation. In particular, in a more recent work, the authors studied the effect of tuning of the electron-donor unit of push-pull porphyrazines [87] (Figure 6), showing its effect on both adsorption and electron injection processes, thus highlighting that porphyrazine design is a delicate process with a significant effect on the electronic properties of organic dyes and therefore on DSSC operation.…”

“…In particular, in a more recent work, the authors studied the effect of tuning of the electron-donor unit of push-pull porphyrazines [87] (Figure 6), showing its effect on both adsorption and electron injection processes, thus highlighting that porphyrazine design is a delicate process with a significant effect on the electronic properties of organic dyes and therefore on DSSC operation. In particular, in a more recent work, the authors studied the effect of tuning of the electron-donor unit of push-pull porphyrazines [87] (Figure 6), showing its effect on both adsorption and electron injection processes, thus highlighting that porphyrazine design is a delicate process with a significant effect on the electronic properties of organic dyes and therefore on DSSC operation. Variations on the push-pull structure have been studied on other several chromophores such as distyryl boron dipyrromethenes as near-infrared sensitizers [88], exhibiting a wide absorption range from UV-visible to near-infrared.…”

“…Figure 6. Chemical structures of A3B panchromatic push-pull porphyrazines studied in reference[87], still incorporating the electron-withdrawing B moiety of TT112 presented in Figure5but with subunits made of pyrrole rings substituted with different donor groups. No permission required.…”