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 x 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 x 10(8) and 16.9 x 10(8) s(-1), respectively, while their rate constants of separation into free ions are 1.6 x 10(8) and 1.1 x 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.