Cycloreversion Induced by Charge-Transfer Excitation of Electron Donor-Acceptor Complexes. Wavelength-Dependent Photochemistry of Dianthracene

Article abstract of DOI:10.1021/ja00310a006

The electron donor-acceptor or EDA complexes of dianthracene (An2 is the ?-dimer of anthracene) and its derivatives with tetracyanoethylene show two unusually well-resolved charge-transfer (CT) bands.Specific irradiation of each of these absorption bands with monochromatic light at five selected wavelengths ranging from 405 to 577 nm leads to the clean cycloreversion of An2 to anthracene.The striking wavelength-dependent quantum efficiency for cycloreversion is analyzed in terms of two different CT ion pairs derived from the photoexcitation of the first and second absorption bands, which correspond to electron promotion from the HOMO and SHOMO (second highest occupied molecular orbital) of the dianthracene donor, respectively.Orbital correlations between dianthracene ?-dimer reveal that electron promotion from the SHOMO of dianthracene leads to an excited radical ion An2(+) which is more dissociative than that derived from the HOMO transition.