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

Diana-Paola Medina,Javier Fernández-Ariza,Tomás Torres,M Salomé Rodríguez-Morgade,Frédéric Sauvage,Maxence Urbani

doi:10.3390/molecules26082129

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 β-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.

Highlights

Owing to the vast number of studies performed on porphyrins (Ps) and phthalocyanines (Pcs) together with their applications in manifold fields, these porphyrinoids constitute the two main representatives of tetrapyrrolic macrocycles
This effective interaction of cyanovinyl substitution with the macrocycle is evidenced in UV/Vis spectroscopy, where a large splitting of the Q-band indicates strong desymmetrization of the Pz
Phthalocyanines consist of porphyrazines containing four fused benzene rings, the chemistry and applications of the former are so extensive [6] that they are considered a group apart, and the name of “porphyrazine” is usually reserved to tetraazaporphyrins that do not contain such fused benzene rings

Summary

Introduction

Owing to the vast number of studies performed on porphyrins (Ps) and phthalocyanines (Pcs) together with their applications in manifold fields, these porphyrinoids constitute the two main representatives of tetrapyrrolic macrocycles. Phthalocyanines consist of porphyrazines containing four fused benzene rings, the chemistry and applications of the former are so extensive [6] that they are considered a group apart, and the name of “porphyrazine” is usually reserved to tetraazaporphyrins that do not contain such fused benzene rings. Both Pcs and Pzs display absorption envelopes dominated by the so-called B and Q-bands. In octaamino-Pzs, the MgPz/MgPz+ and MgPz/MgPz− couples appear at −0.27 V and −1.61 V, respectively [11], whereas the MgPc/MgPc+ and MgPc/MgPc− couples of the corresponding octaamino-Pcs are detected at +0.09 and −1.36 V, respectively [10]

Methods

Results

Conclusion