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Effect of Substitution on the ESR Spectra and Electronic Ground State of ZnTPP Cation Radicals
Author(s) -
Dave Paresh C.,
Srinivas D.
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(200003)2000:3<447::aid-ejic447>3.0.co;2-z
Subject(s) - chemistry , radical , substitution (logic) , spectral line , ground state , photochemistry , electronic structure , computational chemistry , atomic physics , organic chemistry , physics , astronomy , computer science , programming language
Zinc(II) complexes of substituted tetraphenylporphyrins, Zn[T(X–P)P], where X = H, p ‐F, p ‐Cl, m ‐Cl, p ‐CH 3 O, and m ‐CH 3 O, have been synthesized and characterized. Peripheral substitution shows marked changes in the chemical shifts of the phenyl proton resonances and E 1/2 values of the redox couples in the anodic region while the UV/Vis spectra are unaffected. The monocation radicals of these complexes are generated by chemical oxidation with bromine. The ESR spectra reveal the formation of two types of radical species, Zn[T(X–P)P] + · Br – (species I ) and Zn[T(X–P)(Br n –P)] + · Br – (species II ): Species I at 298 K shows a spectrum, with well‐resolved bromine hyperfine features, characteristic of a 2 A 2u electronic ground state while species II , except for the complex with X = m ‐CH 3 O, shows a featureless, isotropic resonance attributable to a 2 A 1u state. Zn[T( m ‐CH 3 O–P)(Br n –P)] + · Br – , on the other hand, exhibits nine resolved nitrogen hyperfine features corresponding to a 2 A 2u state. Variable temperature ESR spectra (77–298 K) indicate reduction in the bromine and nitrogen hyperfine coupling constants and an increase in the g value of species I from 2.0049 to 2.0060 with lowering temperature and suggest a labile electronic ground state for species I . The p ‐CH 3 O substituted complex exhibits an electronic transformation from 2 A 2u to 2 A 1u while the remaining complexes, including m ‐CH 3 O, show a transformation from 2 A 2u to an admixed 2 A 1u / 2 A 2u state. The effect of substitution on the variable temperature ESR spectra are discussed.