Energetic Probing for the Electron Transfer Reactions Sensitized by 9,10-Dicyanoanthracene and 9-Cyanoanthracene and Their Modified Zeolite Particles

Abstract

The photooxidation of diphenylamine (DPA) and triphenylphosphine (P(C6H5)3) sensitized by 9,10-dicyanoanthracene (DCA) and 9-cyanoanthracene (CA) was investigated in this work. Theoretically and evidently, DPA could quench the excited DCA and CA (denoted DCA* and CA*) via an electron transfer pathway. The Stern−Volmer quenching rate constants were calculated to be ca. 4 × 104 equiv-1 s-1 for both DCA* and CA*. In contrast to DPA, P(C6H5)3 showed no quenching effects on DCA* and CA* and only P(C6H5)3 was excited along with the sensitizers upon the exposure to UV light (260 nm). The formal potentials of DCA*/- and CA*/- were thus concluded to be located between the formal potentials of DPA+/0 (1.5 V vs SCE) and the formal potentials of P(C6H5)3+/0 (ca. 2 V vs SCE). Oxygen could significantly quench DCA* and CA* via an energy transfer pathway. Photooxygenations of P(C6H5)3 and (C6H5)3CH were carried out using the DCA- and CA-exchanged zeolite particles (denoted NaY/DCA and NaY/CA) as the heterogeneous catalysts. Noticeably, as DCA and CA were adsorbed on the zeolite particles, their excited states became longer-lived (ca. 100 ns) as compared to the solution counterparts (ca. 13 ns under nitrogen), which also caused a severe retardation to the electron transfer between the electron donors outside the zeolite particles and the DCA*(NaY) and CA*(NaY). Iron(II) ions could activate these retarded photoinduced electron transfer reactions. Under the photocatalysis of the NaY/Fe2+/DCA particle, P(C6H5)3O could be generated from P(C6H5)3 in aerated CH3CN. If AgF was added, the major product shifted from P(C6H5)3O to P(C6H5)3F2. Under a similar photolysis condition, (C6H5)3CF was the major derivative of triphenylmethane. These results suggested that P(C6H5)3+, P(C6H5)32+, and (C6H5)3C+ had been generated. Electron transfer reaction was evidenced to play a key role in the NaY/Fe2+/DCA- and NaY/Fe2+/CA-sensitized photoreactions.