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Title: Models for photosynthetic reaction center: Synthesis, structure and electrochemical properties of a cofacial di-palladium bisporphyrin
Authors: Chaudhary, Arvind
Patra, Ranjan
Rath, Sankar Prasad
Keywords: Porphyrins
Porphyrin dimers
Pi-pi interactions
Molecular motions
Electrochemical properties
Issue Date: Sep-2011
Publisher: NISCAIR-CSIR, India
Abstract: A novel cofacial dipalladium(II) bisporphyrin (Pd2DEP) 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 CH2Cl2, 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 Pd2DEP and also provides a means of switching, in a clapping motion, from a closed to an open Pacman structure under electrochemical stimulus.
Description: 1436-1442
ISSN: 0975-0975(Online); 0376-4710(Print)
Appears in Collections:IJC-A Vol.50A(09-10) [September-October 2011]

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