Laser photolysis studies of endothermic triplet energy transfer in solution

用纳秒激光闪光光解方法测定了溶液中三重态α-萘基苯基酮(NPK)到α-萘甲基苯硫醚(NMPs)的双分子速率常数(Δ_q)和能量转移效率(Tet&gt)，其中能差为1.7kcal。根据κ_q值的Arrhenius图，得到内能三重态能量转移的活化能(ΔE_a)为2.6kcal摩尔~(-1)~(-1)，大于吸热能隙(ΔE_T=1.7kcal~(？)研究了2，11-二氮杂并[3，3](9，10)-2，11-二氮杂并[3，3](9，10)-2，11-二氮杂并[3，3](9，10)菲环番衍生物5的光致异构体标题双二氮杂菲体系6的三重态敏化光反应。在XT-SENSI…上通过绝热环反和形式[2πa+2πa+2σS]重排，得到了光致异构体6、环芳烃5和新的多环产物7。用激光光解技术测定了形成环5的最大量子产率(0.69)和形成多环7的上限效率(0.31)。对于BP敏化的光解异构体6，除了环磷烷5和多环7外，还通过Paterno-Buchi反应生成了氧杂环烷8。光致异构体6对三重态光敏剂的猝灭速率常数(κ_q)，BP(3.4×10^8dm^3molt；-1)比XT(5.0x10^9dm^3)小一个数量级，光异构体6的三重态能级估算为71kcal。基于κ_q与三重态施主-受主能隙的关系。敏化光解所涉及的光化学和光物理过程在能量反应图中进行了总结和详细的讨论。较少

A bimolecular rate constant (κ_q) and an efficiency (α_<TET>) of an endoergonic triplet energy transfer from triplet α-naphthyl phenyl ketone(NPK) to α-naphthylmethyl phenyl sulfide(NMPS) in solution, where the energy difference (ΔE_T) is 1.7 kcal mol^<-1>, have been determined by means of nanosecond laser flash photolysis. Base on the Arrhenius plots of the κ_q value for the NPK-NMPS system, an activation energy (ΔE_a) for the endoergonic triplet energy transfer is found to be 2.6 kcal mol^<-1>, which is larger than the endothermic energy gap (ΔE_T=1.7 kcal mol^<-1>). The endoergonic triplet energy transfer in solution is demonstrated to proceed with the aid of thermal activation for the first time.The triplet-sensitized photoreactions of the title biplanophane system 6, the photoisomer of a 2.11-diaza[3,3](9,10)anthracenoparacyclophane derivative 5, were investigated by stationary and laser flash photolyses using xanthone(XT) and benzophenone(BP) as triplet sensitizers. Upon XT-sensi … More tized irradiation of the photoisomer 6, a cyclophane 5 and a novel polycyclic product 7 were obtained via an adiabatic cycloreversion and a formal [2πa+2πa+ 2σs] rearrangement. The maximum quantum yield for formation of the cyclophane 5 (0.69) and the upper-limit efficiency for formation of the polycycle 7 (0.31) were determined by laser photolysis techniques. For BP-sensitized photolysis of the photoisomer 6, an oxetane 8 was formed via a Paterno-Buchi reaction in addition to cyclophane 5 and polycycle 7. Quenching rate constant (κ_q) of the triplet sensitizers by photoisomer 6 was smaller by one order of magnitude for BP (3.4x 10^8 dm^3 mol^<-1> s^<-1>) than for XT (5.0x10^9 dm^3 mol^<-1> s^<-1>) and the triplet energy level of photoisomer 6 was estimated as 71 kcal mol^<-1> based on the relationship between κ_q and triplet donor-acceptor energy gap. The photochemical and the photophysical processes involved in the sensitized photolyses are summarized in an energetic reaction diagram and discussed in detail. Less