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

摘要

The photooxidation of diphenylamine (DPA) and triphenylphosphine (P(C_6H_5)_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 * 10~4 equiv~(-1) s~(-1) for both DCA~* and CA~*. In contrast to DPA, P(C_6H_5)_3 showed no quenching effects on DCA~* and CA~* and only P(C_6H_5)_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(C_6H_5)_3~(+/0) (ca. 2 V vs SCE). Oxygen could significantly quench DCA~* and CA~* via an energy transfer pathway. Photooxygenations of P(C_6H_5)_3 and (C_6H_5)_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/Fe~(2+)/DCA particle, P(C_6H_5)_3O could be generated from P(C_6H_5)_3 in aerated CH_3CN. If AgF was added, the major product shifted from P(C_6H_5)_3O to P(C_6H_5)_3F_2. Under a similar photolysis condition, (C_6H_5)_3CF was the major derivative of triphenylmethane. These results suggested that P(C_6H_5)_3~+, P(C_6H_5)_3~(2+), and (C_6H_5)_3C~+ had been generated. Electron transfer reaction was evidenced to play a key role in the NaY/Fe~(2+)/DCA- and NaY/Fe~(2+)/CA-sensitized photoreactions.