Photoswitching of the magnetic properties of one-dimensional pi-electron systems

The change of the magnetic properties of the isomeric forms of photorespons ive model polymers with photochromic diarylethene elementary units substitu ted with radical centers are investigated theoretically. The band theory is used to calculate the effective exchange integral of the photoisomeric one -dimensional many-electron pi -systems. It is shown that the magnetic prope rties can be reversibly switched from ferromagnetic to non-magnetic in some cases. In other cases the magnitude of the ferromagnetic exchange interact ion is either increased or decreased in the photoisomers. The practicabilit y of the photocyclization is estimated using reactivity indices in the exci ted state calculated in pi -electron approximation with the HMO method. In most cases a reversible photocyclization (ring opening) should be possible. (C) 2001 Elsevier Science B.V. All rights reserved.