Porphyrin Diacid-Polyelectrolyte Assemblies: Effective Photocatalysts in Solution

Abstract

Developing effective and versatile photocatalytic systems is of great potential in solar energy conversion. Here we investigate the formation of supramolecular catalysts by electrostatic self-assembly in aqueous solution: Combining positively charged porphyrins with negatively charged polyelectrolytes leads to nanoscale assemblies where, next to electrostatic interactions, π-π interactions also play an important role. Porphyrin diacid-polyelectrolyte assemblies exhibit a substantially enhanced catalytic activity for the light-driven oxidation of iodide. Aggregates with the hexavalent cationic porphyrin diacids show up to 22 times higher catalytic activity than the corresponding aggregates under neutral conditions. The catalytic activity can be increased by increasing the valency of the porphyrin and by choice of the loading ratio. The structural investigation of the supramolecular catalysts took place via atomic force microscopy and small angle neutron scattering. Hence, a new facile concept for the design of efficient and tunable self-assembled photocatalysts is presented.

Molecular Engineering of Free‐Base Porphyrins as Ligands—The N−H⋅⋅⋅X Binding Motif in Tetrapyrroles

“…Additionally,porphyrin diacid-polyelectrolyte supramolecules formed via electrostatic self-assembly in aqueous solution were used as effective photocatalytic systems for iodide oxidation. [101] Herein, the cationic porphyrin architectures showed asignificantly higher catalytic activity than aggregates under neutral conditions.P orphyrin dications have also generated some interest, for example,innonlinear optics (NLO), where laserinduced protonation of free-base porphyrin in chloroform gave apositive nonlinear absorption (NLA) due to conformational distortion. [102] Often, the more elusive porphyrin monocations are also saddle-distorted, although tendentially less than the corresponding diacids [103] and stand as a" missing species" in porphyrin chemistry since they are generally difficult to produce,c haracterize,a nd isolate.P orphyrin monoacids are usually less stable than their diprotonated counterparts;i tis likely that al arge saddle-distortion destabilizes the monoacids because their out-of-plane distortion significantly reduces the steric crowding of the remaining unprotonated nitrogen atom.…”

“…Specifically, the dihydrochloride salt of 64 , [H 4 DPP 2+ ][Cl − ] 2 , gave supramolecular architectures by self‐assembly based on intermolecular π—π interactions that could host tetrathiafulvalene and p ‐aminophenol. Additionally, porphyrin diacid–polyelectrolyte supramolecules formed via electrostatic self‐assembly in aqueous solution were used as effective photocatalytic systems for iodide oxidation . Herein, the cationic porphyrin architectures showed a significantly higher catalytic activity than aggregates under neutral conditions.…”

Visible-light photooxidation in water by 1O2-generating supramolecular hydrogels

“…[23][24][25][26][27][28] Most recent examples of hydrogel photocatalysts 29 involve co-assembling of the photocatalysts with gelators, where catalysts and gelators are two separate components. These hydrogel photocatalysts were used for the oxidation of iodide, 30 hydrogen production, 31 polymer crosslinking, 32 and articial photosynthesis. 33,34 There remain, however, several drawbacks with hydrogel photocatalysts, including the limited control of positioning and accessibility of photoactive sites and the possibility of dissociation of non-covalently bound photoactive sites from the gel.…”

Enhanced In-Vitro Hemozoin Polymerization by Optimized Process using Histidine-Rich Protein II (HRPII)

“…Following the reports, the heme (ferrous porphyrin complexes) has good conductivity and biocompatibility. It shows the different metal centers incorporated within the tetradentate ligand and the physical properties have a conformational flexibility of porphyrins with conductivity [7,8,9,10,11]. In addition, the heme has been found to have an oxidation-reduction activity, and it has also been reported to have a great influence on electron transfer under an oxidation-reduction reaction [34,35].…”

“…For example, conductive polymers containing porphyrin complexes, such as zinc-tetraphenylporphyrin (Zn), zinc-tetrabenzoporphyrin (Zn), iron-metalloporphyrins (Fe), ruthenium-metalloporphyrins (Ru), and osmium-metalloporphyrins (Os), are some of the well-known functional materials. These porphyrin structures show different metal centers incorporated within the tetradentate ligand, and the physical properties have a conformational flexibility of porphyrins with conductivity [7,8,9,10,11]. Thus, it is advantageous to develop advanced materials through control at the molecular level.…”