Charge-Transfer Photochemistry from the Donor-Acceptor Complexes of Anthracenes with Tetranitromethane
Journal of Organic Chemistry
The formation of electron donor-acceptor or EDA complexes of a series of 9-substituted and 9,lO-disubstituted anthracenes with tetranitromethane (TNM) can be visually observed in dichloromethane solutions. The colors arise from charge-transfer (CT) transitions from the aromatic donor (An) to the tetranitromethane acceptor. Specific irradiation of the CT absorption band at X > 500 nm leads to the rapid bleaching of the solution, and high yields of photoadducts 1 can be isolated especially from those anthracenes bearing electron-withdrawing substituents. X-ray crystallography establishes the photoadducts 1 to derive from an overall anti addition of the TNM fragments, C(NO& and NOz, across the meso positions of 9-bromo- and 9-phenylanthracene. The high quantum yields me associated with the efficient dissociative electron transfer accompanying the charge-transfer excitation of the 1:l EDA complex. The subsequent multistep pathway by which the geminate species [An+-, C(N02)3-, NOz] combine regiospecifically and stereospecifically to form the photoadduct 1 is described. The structural elucidation of the byproducts underscores the efficiency of ion-pair and radical-pair interactions following the CT excitation of EDA complexes.
Masnovi, J. M.; Kochi, J. K. Charge-transfer photochemistry from the donor-acceptor complexes of anthracenes with tetranitromethane. J. Org. Chem. 1985, 50, 5245-5255.