Phosphorus(V) Porphyrin-Manganese(II) Terpyridine Conjugates: Synthesis, Spectroscopy, and Photo-Oxidation Studies on a SnO2 Surface

Prashanth K. Poddutoori, Gary N. Lim, Melanie Pilkington, Francis D'Souza, Art Van Der Est

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9 Scopus citations

Abstract

A major challenge in designing artificial photosynthetic systems is to find a suitable mimic of the highly oxidizing photoactive species P680 in photosystem II. High-potential phosphorus(V) porphyrins have many attractive properties for such a mimic but have not been widely studied. Here, we report the synthesis and photophysical characterization of a novel phosphorus(V) octaethylporphyrin-oxyphenyl-terpyridine conjugate (PPor-OPh-tpy, 1) and its corresponding manganese(II) complex (PPor-OPh-Mn(tpy)Cl2, 2). The X-ray structure of 2 shows that the Mn(II) and P(V) centers are 11.783 Å apart and that the phenoxy linker is not fully conjugated with the terpyridine ligand. The porphyrin fluorescence in 1 and 2 is strongly quenched and has a shorter lifetime compared to a reference compound without the terpyridine ligand. This suggests that electron transfer from tpy or Mn(tpy) to the excited singlet state of the PPor may be occurring. However, femtosecond transient absorbance data show that the rate of relaxation to the ground state in 1 and 2 is comparable to the fluorescence lifetimes. Thus, if charge separation is occurring, its lifetime is short. Because both 1 and 2 are positively charged, they can be electrostatically deposited onto the surface of negatively charged SnO2 nanoparticles. Freeze-trapping EPR studies of 2 electrostatically bound to SnO2 suggest that excitation of the porphyrin results in electron injection from 1PPor∗ into the conduction band of SnO2 and that the resulting PPor•+ species acquires enough potential to photo-oxidize the axially bound Mn(II) (tpy) moiety to Mn(III) (tpy).

Original languageEnglish (US)
Pages (from-to)11383-11395
Number of pages13
JournalInorganic chemistry
Volume55
Issue number21
DOIs
StatePublished - Nov 7 2016

Bibliographical note

Funding Information:
This work was supported by National Sciences and Engineering Research Council Canada (Discovery grants to A.v.d.E. and M.P.) and the Canada Foundation for Innovation (New Opportunities grant to MP and Innovation Fund grant to A.v.d.E.). Support by the National Science Foundation (Grant 1401188 to F.D.) is acknowledged.

Publisher Copyright:
© 2016 American Chemical Society.

Copyright:
Copyright 2016 Elsevier B.V., All rights reserved.

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