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A semiempirical investigation of interelectronic exchange coupling in bisected poly(1,4‐phenylene) polycation model systems
Author(s) -
Lahti Paul M.
Publication year - 1992
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560440509
Subject(s) - dication , chemistry , singlet state , phenylene , ferromagnetism , ground state , diradical , computational chemistry , triplet state , crystallography , excited state , atomic physics , condensed matter physics , polymer , molecule , physics , organic chemistry
AM 1 SCF ‐ MO ‐ CI computations find the bisected biphenyl dication to have nearly degenerate triplet and singlet states, with the lowest‐energy state being a quininoid singlet planar dication. The bisected perchlorobiphenyl dication favors a triplet ground state by a small amount (0.4‐1.9 kcal/mol), in qualitative agreement with recent experimental findings and with theoretical expectations that such an orthogonal open‐shell pi‐system should exhibit ferromagnetic exchange coupling. The higher oligomeric bisected para ‐linked phenylenes polycations do not show an appreciable computational preference for a high‐spin multiplicity ground state either with or without perchlorine substitution. Chlorine substitution para to the 1,1′‐linkage may lend a unique stabilization to the biphenyl system, which is not available in higher oligomeric analogs of poly(1,4‐phenylene)s. The small magnitude of ferromagnetic exchange in these systems suggests that small geometric or substituent effects may confound experimental efforts to design polymeric ferromagnetic materials by this strategy. © 1992 John Wiley & Sons, Inc.