Proton-Induced Electro-Transfer Reaction from Triplet Methoxynaphthalenes to Benzophenone via Triplet Exciplex

Article abstract of DOI:10.1021/j100202a054

A laser flash photolysis study at 355 nm has been carried out on acetonitrile-water (4:1 v/v) mixtures of the methoxynaphthalene-benzophenone-H2SO4 system.It is found that the proton-assisted photoionization reaction of triplet 1- and 2-methoxynaphthalene (ROMe) produced by triplet sensitization of benzophenone (BP) effectively occurs to produce the corresponding methoxynaphthalene cation radical (ROMe(1+.)) and benzophenone ketyl radical (>C(.)OH).The triplet energy-transfer reaction from triplet benzophenone (³BP^*) to ROMe takes place as the primary event to produce triplet methoxynaphthalene (³ROMe^*).The 1:1 triplet exciplex ³(ROMe...>CO)^* having a weak charge-transfer structure is readily formed between ³ROMe^* and BP with the equilibrium constants K₁ (10.1 M^-1 for 1ROMe; 4.0 M^-1 for 2ROMe at 290 K).In the presence of protons, the triplet protonated exciplex ³(ROMe...>C(1+)OH)^* is also produced by protonation to ³(ROMe...>CO)^*.Subsequently, the intraexciplex electron-transfer reaction in ³(ROMe...>C(1+)OH)^* takes place effectively, resulting in the formation of ROMe(1+.) and >C(.)OH.The presence of protons in the ROMe-BP system assists the photoionization of ROMe with the much lower energy (triplet energy of ROMe) than its ionization potential.The reaction mechanism is discussed in detail.