Photoinduced Electron Transfer of PAMAM Dendrimer–Zinc(II) Porphyrin Associates at Polarized Liquid|Liquid Interfaces

Abstract

The heterogeneous photoinduced electron-transfer reaction of the ion associates between NH2-terminated polyamidoamine (PAMAM) dendrimers and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato zinc(II) (ZnTPPS(4-)) was studied at the polarized water|1,2-dichloroethane (DCE) interface. The positive photocurrent arising from the photoreduction of ZnTPPS(4-) by a lipophilic quencher, decamethylferrocene, in the interfacial region was significantly enhanced by the ion association with the PAMAM dendrimers. The photocurrent response of the dendrimer-ZnTPPS(4-) associates was dependent on the pH condition and on the generation of dendrimer. A few cationic additives such as polyallylamine and n-octyltrimethyammonium were also examined as alternatives to the PAMAM dendrimer, but the magnitude of the photocurrent enhancement was rather small. The high photoreactivity of the dendrimer-ZnTPPS(4-) associates was interpreted mainly as a result of the high interfacial concentration of photoreactive porphyrin units associated stably with the dendrimer which was preferably adsorbed at the polarized water|DCE interface. The photochemical data observed in the second and fourth generation PAMAM dendrimer systems demonstrated that the higher generation dendrimer which can incorporate a porphyrin molecule more completely in the interior is less efficient for the photocurrent enhancement at the interface. These results indicated that the photoreactivity of ionic reactant at a polarized liquid|liquid interface can readily be modified via ion association with the charged dendrimer.

Preparation and crystal structure of tetraoctylphosphonium tetrakis(pentafluorophenyl)borate ionic liquid for electrochemistry at its interface with water

“…In metal ion extraction, a hydrophobic ligand is typically dissolved in the organic phase and coordinates with the metal ion either interfacially or in the bulk organic/aqeuous phase [13,14]. Conventional means of separation have been through physical mixing of the two phases [9,15]; however, as previously demonstrated [10][11][12]16], this process can also be investigated electrochemically using liquid|liquid electrochemistry performed at a polarizable interface between two immiscible electrolytic solutions (ITIES) [13,14,[17][18][19][20][21]. Furthermore, in order to reduce samples sizes and improve sensitivity, a micro-ITIES is often employed, such as at the tip of a pulled borosilicate glass capillary [11,16,[22][23][24].…”

Decorating soft electrified interfaces: From molecular assemblies to nano-objects

“…Photoinduced electron transfer reaction was also observed for similar porphyrin dimer and hexanethiolate monolayer protected gold nanoclusters dissolved in the DCE phase [76]. ZnTPPS 4+ association with positively charged polyallylamine polyelectrolyte and polyamidoamine dendrimers can also contribute to photocurrent amplification [77]. The best performance found for dendrimer-porphyrin conjugate was attributed to electrochemically driven interfacial deposit formation with high porphyrin loading and stable associate formation [41].…”

Pathway Complexity in Supramolecular Porphyrin Self-Assembly at an Immiscible Liquid|Liquid Interface

“…30 Due to their similarities to natural dyes functioning in photosynthetic systems, supramolecular assemblies of zinc(II) 5,10,15,20-(tetra-4-carboxyphenyl)porphyrin (ZnTPPc) molecules at immiscible liquid|liquid interfaces are of particular interest for solar energy conversion and storage applications. 31,32 Early work demonstrated that photocurrents obtained at porphyrin nanostructure functionalised liquid|liquid interfaces are remarkably dependent on the light polarization, indicating a well-ordered self-assembled nanostructure due to the templating interaction of the interface. 33 Recently, our group demonstrated that these interfacial ZnTPPc nanostructures are stabilized by cooperative hydrogen bonding and likely represent metastable or kinetically trapped non-equilibrium nanostructures.…”