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|Title:||Models for photosynthetic reaction center: Synthesis, structure and electrochemical properties of a cofacial di-palladium bisporphyrin|
Rath, Sankar Prasad
|Abstract:||A novel cofacial dipalladium(II) bisporphyrin (Pd<sub>2</sub>DEP) of Pacman-type is reported herein. Structural characterization suggests very strong π-π interactions between two planar porphyrins that closely mimic the spatial orientation observed in the so called ‘special pair’. The electrochemical response reveals four consecutive ring-centered oxidations in CH<sub>2</sub>Cl<sub>2</sub>, indicative of strong through-space electronic communication between two redox-active Pd-porphyrins. At 0.66V, one Pd-porphyrin unit is oxidized to generate a radical cation at a potential much lower than that of monomeric unit (PdOEP), owing to the increased electron density in the bisporphyrin scaffold. However, due to the presence of strong inter-macrocyclic interactions, the second Pd-porphyrin is then oxidized at a significantly higher potential (0.97 V) to produce radical cation species. In the bis(radical cation) state, electrostatic repulsion induces change in the geometry due to flexible spacer which eventually forces an increase in the porphyrin-porphyrin distance. As a result, the second oxidation of both the porphyrin radical cations is observed at 1.42 V as a single reversible two-electron process. The overall oxidation process thus demonstrates strong electrostatic communication between the two macrocycles in Pd<sub>2</sub>DEP and also provides a means of switching, in a clapping motion, from a closed to an open Pacman structure under electrochemical stimulus.|
|Appears in Collections:||IJC-A Vol.50A(09-10) [September-October 2011]|
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|IJCA 50A(09-10) 1436-1442.pdf||270.61 kB||Adobe PDF||View/Open|
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