Investigation of the Photoinduced Electron Transfer Reaction between 9,10-Dicyanoanthracene and 1-Methylnaphthalene in Acetonitrile Using Picosecond Transient Grating Spectroscopy

A spectroscopic and kinetic study of the photoinduced electron transfer (ET) reaction between 9,10-dicyanoanthracene (DCA) and 1-methylnaphthalene (MNA) in acetonitrile using the transient grating technique is reported. Apart from the bands assigned to 1 DCA* and DCA •-, the transient spectrum exhibits a band located at 580 nm and ascribed to MNA 2 •+ . This species is generated upon reaction of a second donor molecule with a 1:1 complex to form a 1:2 complex (DCA •- ·MNA 2 •+ ). Using chloranil as electron acceptor, the rate constant of this reaction has been measured to be 6.8 × 10 9 M -1 s -1 . From the donor concentration dependence of the kinetics of DCA •- diffraction intensity and of the free ion yield, the rates of back ET to the ground state within the 1:1 and the 1:2 complexes have been determined to be equal to 1.8 × 10 8 and 16.9 × 10 8 s -1, respectively, while their rate constants of separation into free ions are 1.6 × 10 8 and 1.1 × 10 8 s -1, respectively. These values have been obtained assuming a reaction scheme in which both forward and backward ET essentially take place at contact distance. In the case of the 1:1 complex, however, charge recombination within a loose ion pair cannot be ruled out.