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Multiporphyrin Arrays on Cyclophosphazene Scaffolds: Synthesis and Studies
Author(s) -
Pareek Yogita,
Ravikanth Mangalampalli
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201200273
Subject(s) - porphyrin , proton nmr , chemistry , metalation , ring (chemistry) , crystallography , two dimensional nuclear magnetic resonance spectroscopy , hexa , spectral line , nmr spectra database , mass spectrum , stereochemistry , photochemistry , ion , organic chemistry , physics , astronomy
The stable and robust cyclotriphosphazene and cyclotetraphosphazene rings were used as scaffolds to prepare hexa‐ and octaporphyrin arrays by treating N 3 P 3 Cl 6 and N 4 P 4 Cl 8 , respectively, with 5‐(4‐hydroxyphenyl)‐10,15,20‐tri( p ‐tolyl)porphyrin (N 4 core) or with its thiaporphyrin analogues (N 3 S and N 2 S 2 cores) in THF in the presence of Cs 2 CO 3 under simple reaction conditions. Thiaporphyrins were examined in addition to the normal porphyrin to tune the electronic properties of the resultant arrays. Observation of the molecular ion peaks in the mass spectra confirmed the molecular structures of the arrays. 1D and 2D NMR techniques were employed to characterize the multiporphyrin arrays in detail. The 1 H NMR spectra of the multiporphyrin arrays each show a systematic set of signals, indicating that the porphyrin units are arranged in a symmetrical fashion around the cyclophosphazene rings. All signals in the 1 H NMR spectra were assigned with the aid of COSY and NOESY experiments. The protons of each porphyrin unit are subject to upfield and downfield shifts because of the ring‐current effects of neighboring porphyrin units. Optical, electrochemical, and fluorescence studies of the arrays indicated that the porphyrin units retain their independent ground‐ and excited‐state characteristics. Cu II and Ni II derivatives of hexaporphyrin and octaporphyrin arrays containing N 4 porphyrin units and N 3 S porphyrin units were synthesized, and complete metalation of the arrays was confirmed by their mass spectra and by detailed NMR characterization of the Ni II derivatives of hexa‐ and octaporphyrin arrays containing N 4 porphyrin units. Electrochemical studies indicated that Cu II and Ni II ions present in the thiaporphyrin units of the arrays can be stabilized in the +1 oxidation state, which is not possible with arrays containing normal porphyrin units.