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para ‐Phenylene‐Bridged Spirobi(triarylamine) Dimer with Four Perpendicularly Linked Redox‐Active π Systems
Author(s) -
Ito Akihiro,
Hata Kazuhira,
Kawamoto Kensuke,
Hirao Yasukazu,
Tanaka Kazuyoshi,
Shiro Motoo,
Furukawa Ko,
Kato Tatsuhisa
Publication year - 2010
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.201000848
Subject(s) - moiety , chemistry , dication , radical ion , unpaired electron , dimer , delocalized electron , redox , photochemistry , electron paramagnetic resonance , diradical , crystallography , singlet state , radical , stereochemistry , molecule , ion , excited state , nuclear magnetic resonance , inorganic chemistry , physics , organic chemistry , nuclear physics
para ‐Phenylene‐bridged spirobi(triarylamine) dimer 2 , in which π conjugation through four redox‐active triarylamine subunits is partially segregated by the unique perpendicular conformation, was prepared and characterized by structural, electrochemical, and spectroscopic methods. Quantum chemical calculations (DFT and CASSCF) predicted that the frontier molecular orbitals of 2 are virtually fourfold degenerate, so that the oxidized states of 2 can give intriguing electronic and magnetic properties. In fact, the continuous‐wave ESR spectroscopy of radical cation 2 .+ showed that the unpaired electron was trapped in the inner two redox‐active dianisylamine subunits, and moreover was fully delocalized over them. Magnetic susceptibility measurements and pulsed ESR spectroscopy of the isolated salts of 2 , which can be prepared by treatment with SbCl 5 , revealed that the generated tetracation 2 4+ decomposed mainly into a mixture of 1) a decomposed tetra(radical cation) consisting of a tri(radical cation) moiety and a trianisylamine radical cation moiety (≈75 %) and 2) a diamagnetic quinoid dication in a tetraanisyl‐ p ‐phenylendiamine moiety and two trianisylamine radical cation moieties (≈25 %). Furthermore, the spin‐quartet state of the tri(radical cation) moiety in the decomposed tetra(radical cation) was found to be in the ground state lying 30 cal mol −1 below the competing spin‐doublet state.