Fourth-rank hypermagnetizability of medium-size planar conjugated molecules and fullerene

The fourth-rank hypermagnetizability tensor of a series of planar conjugated molecules—i.e., aromaticnaphthalene, nonaromatic borazine, antiaromatic flattened cyclo-octatetraene, pentalene, indacene, and the60-carbon fullerene,—has been evaluated at the coupled Hartree-Fock level of accuracy, within the conventionalcommon-origin approach, via extended Gaussian basis sets. The theoretical predictions indicate thatantiaromatic molecules are characterized by out-of-plane hypermagnetizability components much bigger thanbenzene’s. The fullerene cage has a hypermagnetizability exceeding that of planar aromatics by three orders ofmagnitude. However, the experimental determination of the hypermagnetizabilities constitutes a big challenge.Chemically substituted carbon clusters seem good candidates for detection of cubic magnetic response. Understandingof the calculated hypermagnetizabilities is eased by plots of the differential electron densityinduced by the applied field. It is found that a strong magnetic field perpendicular to the plane of antiaromaticmolecules causes a distortion of the electron charge density, which tends to break C-C double bonds. Thischarge stretching has a dynamical origin and may be qualitatively explained as a feedback effect due to theLorentz force acting on the electron current density.