Substituent effect on the photoinduced electron-transfer reaction of para-substituted triphenylphosphines sensitised by 9,10-dicyanoanthracene

The photoinduced electron-transfer reaction of para-substituted triphenylph osphines sensitised by 9,10-dicyanoanthracene (DCA) occurred in acetonitril e containing 2 vol% water to form the corresponding triphenylphosphine oxid e. Transient absorption spectral measurements were carried out during 355 n m laser flash photolysis of a mixture of the phosphine and DCA. The electro n transfer from the phosphine to singlet excited DCA initiated the reaction . A para substituent on the benzene ring affects the quantum yields of the phosphine radical cation and phosphine oxide. The back electron transfer fr om the DCA radical anion to the phosphine radical cation governed the quant um yield of the phosphine radical cation. The quantum yield of the phosphin e oxide was dependent on the conjugation between the pi-electron of the ben zene ring and the n-electron of the phosphorus atom in the phosphine radica l cation. The phosphine oxide forms through nucleophilic attack of H2O towa rd the phosphorus atom of the phosphine radical cation, producing the phosp horanyl radical.