Photoswitching of the magnetic properties of one-dimensional π-electron systems: III. Photochromic polymers with polymethine radicals in the elementary units

The switching of the magnetic properties of the photoisomeric structures of polymers with photochromic [2,2]-metacyclophanene, [2,2]-metacyclophanediene, 10-benzylidene-anthrone or 9-benzylidene-9,10-anthracene fragments and polymethine radical fragments of Wurster and Weitz type within the elementary units is investigated theoretically. The band theory is used to calculate the effective exchange interaction of the open-ring and closed-ring photoisomers, respectively. A real switching from a ferromagnetic to an anti-ferromagnetic state of the isomers has been found only for a few polymers, while in most cases an increase or decrease of the effective exchange integral at the photocyclization has been pointed out.