On the diatropic perimeter of iterated altan-molecules.

Ab initio calculations of the current density induced by an external magnetic field in altan-[10,5]coronene 3 (or altan(2)-[10]annulene) indicate the onset of a diatropic current on the outer loop (the "perimeter"), thus in contrast to the intentional design of altan-molecules. Spectral decomposition of the current shows that the failure of the altanisation design can be expected whenever the perimeter of the altan-molecule is of nearly the same size as that of the parent molecule. Equal lengths of these two perimeters always occur in iterated altan-molecules, which contain a cycloacenic fragment. Like longer polyacenes and cycloacenes, altan(2)-[10]annulene 3 and altan-kekulene 2 are predicted to have an open-shell singlet ground state.