Photoswitching of Redox Potentials and Spectroscopic Properties in the UV/vis Region
The photoswitching of optical and electrochemical properties of di-donor, di-acceptor and donor-acceptor substituted photochromic tetrahydropyrene - [2,2]metacyclophanene and dihydropyrene - [2,2]metacyclophanediene systems has been studied theoretically. A switching of the halfwave oxidation and reduction potentials should be possible in the case of bis(pyridinium) and bis(hydroxyphenyl) substituted systems. Because of the relatively great perturbation of the planarity of the π-electron systems by large torsion of the substituents out of the π-electron structure of the photochromic system and the stair-like structure of the ring-opened isomer, relatively large excitation energies for CT transitions have been calculated with the AM1-CI procedure. The ring-closed structures should absorb in the visible spectral region, and the open-ring isomers should have a longest-wavelength absorption in the UV region.