ROLE OF ION-PAIRS IN THE PHOTOCHEMISTRY OF ELECTRON-DONOR ACCEPTOR COMPLEXES - PICOSECOND SPECTROSCOPIC STUDIES OF ARENE TETRACYANOETHYLENE SYSTEMS
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Photochemical excitation of the electron donor-acceptor (EDA) complexes of various 9-substituted anthracenes and indene as electron donors (D) with tetracyanoethylene as the common electron acceptor (A) is examined by means of time-resolved picosecond spectroscopy. It is unequivocally established for the first time that specific irradiation of the charge transfer absorption bands of these EDA complexes leads directly to the radical ion pair [D+A] within the time resolution of the laser pulse. The transient absorptions resulting from these geminate radical ions decay in ~60 ps after excitation. In the case of the anthracene-tetracyanoethylene complexes, the photogenerated radical ion pairs simply undergo rapid back electron transfer to afford the original EDA complex. However, the radical ion pair derived from the indene-tetracyanoethylene complex initially reacts to form a fleeting intermediate, and the original EDA complex is regenerated only after ~500 ps. 1984, American Chemical Society. All rights reserved.
