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The Poly(Radical Cation) of a Star‐Shaped Oligoarylamine — Detection of Excited High‐Spin States
Author(s) -
Hirao Yasukazu,
Ishizaki Haruya,
Ito Akihiro,
Kato Tatsuhisa,
Tanaka Kazuyoshi
Publication year - 2007
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200600666
Subject(s) - chemistry , electron paramagnetic resonance , trifluoroacetic acid , dichloromethane , intramolecular force , excited state , photochemistry , radical ion , spectroscopy , analytical chemistry (journal) , nuclear magnetic resonance , organic chemistry , ion , atomic physics , physics , quantum mechanics , solvent
The intramolecular spin–spin interaction in the highly oxidized species of a star‐shaped oligoarylamine, namely hexakis{4‐[bis( p ‐methoxyphenyl)amino]phenyl}benzene ( 1 ), in which six diphenylamine units are introduced as redox‐active sites into a central hexaphenylbenzene core, has been investigated by EPR spectroscopy. The hexacation‐rich sample was prepared by chemical oxidation with 7.5 equivalents. of [bis(trifluoroacetoxy)iodo]benzene (PIFA) in the presence of 10 vol.‐% trifluoroacetic acid (TFA) in dichloromethane at 195 K. Variable‐temperature EPR measurements provided the non‐Curie temperature dependence of the signal intensity. The fine structure of the EPR spectrum also varies with temperature. In order to identify the spin multiplicity of the generated poly(radical cation), we carried out electron spin transient nutation (ESTN) measurements based on pulsed EPR spectroscopy at various temperatures. From the ESTN spectra, it was found that the high‐spin states are thermally populated with increasing temperature. These results indicate the low‐spin ground state of the poly(radical cation) of 1 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)