Efficient Sunlight Harvesting by A4 β-Pyrrolic Substituted ZnII Porphyrins: A Mini-Review

Abstract

Dye-Sensitized Solar Cells (DSSCs) are a highly promising alternative to conventional photovoltaic silicon-based devices, due to the potential low cost and the interesting conversion efficiencies. A key-role is played by the dye, and porphyrin sensitizers have drawn great interest because of their excellent light harvesting properties mimicking photosynthesis. Indeed, porphyrins are characterized by strong electronic absorption bands in the visible region up to the near infrared and by long-lived π * singlet excited states. Moreover, the presence of four meso and eight β-pyrrolic positions allows a fine tuning of their photoelectrochemical properties through structural modification. Trans -A 2 BC push–pull Zn II porphyrins, characterized by a strong and directional electron excitation process along the push–pull system, have been extensively investigated. On the other hand, A 4 β-pyrrolic substituted tetraaryl Zn II porphyrins, which incorporate a tetraaryl porphyrinic core as a starting material, have received lower attention, even if they are synthetically more attractive and show several advantages such as a more sterically hindered architecture and enhanced solubility in most common organic solvents. The present contribution intends to review the most prominent A 4 β-substituted Zn II porphyrins reported in the literature so far for application in DSSCs, focusing on the strategies employed to enhance the light harvesting capability of the dye and on a comparison with meso -substituted analogs.

Electronic Properties of Electron-Deficient Zn(II) Porphyrins for HBr Splitting

“…The broadening of the B band is the result of the electronic and steric interaction between the porphyrin ring and the BTD moiety of the anchoring unit in the β-pyrrolic position, rather than an additional absorption peak due to the BTD unit itself [30]. Moreover, the spectrum is red-shifted in comparison to that of 2, confirming for the β-substituted molecular architecture a more favorable conjugation and charge transfer between the porphyrin core and the anchoring unit, with increased light-harvesting [31].…”

Second Order Nonlinear Optical Properties of 4-Styrylpyridines Axially Coordinated to A4 ZnII Porphyrins: A Comparative Experimental and Theoretical Investigation

“…Indeed, the asymmetric 10,20-diaryl substituted porphyrin core requires two reaction steps to be achieved and the further insertion of electron-donating and accepting pendants in 5,15-meso positions involves a tedious multistep pathway [30]. Instead, the β-pyrrolic substituted porphyrins, consisting of a more symmetric tetraaryl-substituted porphyrin core, are promptly accessible through a one-pot cyclo-condensation step among pyrrole and selected aldehydes [31,32]. However, the functionalization of β-pyrrolic positions and the subsequent introduction of proper substituents complicates the synthetic route [33,34].…”

The Role of Porphyrinoid Photosensitizers for Skin Wound Healing

“…Porphyrins and analogs are a class of N-heterocyclic macrocycles well-known for their mediation in important biological functions, such as respiration and photosynthesis, but also by their role in a wide range of clinical and non-clinical applications that have high impacts on human life [1][2][3]. Natural tetrapyrrolic macrocycles like heme (iron(II) complex of PP-IX) and chlorophylls (Figure 1), but also the synthetic porphyrins and analogs ones (e.g., benzoporphyrins, chlorins, phthalocyanines) [4,5] are recognized to present unique structural, physicochemical, and photochemical features to be used in the development of dyes for dye-sensitized solar cells (DSSC) [6][7][8][9][10][11][12][13], (chemo) sensors [14][15][16][17][18][19][20], (photo)catalysts [21][22][23][24][25][26][27], biomarkers [14,28,29] or as therapeutic photosensitizers (PS) [30][31][32][33][34][35][36][37][38][39][40], among other applications [1]. The strong absorption usually exhibited by these highly ...…”