Zeolite photochemistry : Investigation of cation-π interaction and diffusion of guest species

1. 沸石内来宾芳香族和稀土电荷补偿阳离子之间能量转移的动力学研究：通过测量脉冲激光激发来宾分子时，来宾芳香族、二苯甲酮和萘与稀土电荷补偿阳离子Tb^<3+>的^5D_4激发态发射的随时间上升和衰减，实时观察了faujasite沸石Y内来宾芳香族、二苯甲酮和萘之间的能量转移（ET）。相对于溶液体系，将客体物种限制在笼内会大大增强发射强度，从而通过促进激发态复合物的形成来促进ET。此外，发射的动力学行为表明，当二苯甲酮分子固定在笼内的质子位点时，萘分子仍然是可移动的，这导致了对Tb^<3+>发射的负载依赖性上升和衰减的显著观察。与激发态复合物的假设更一致的是，直接激发Tb^<3+>的^7F_6→^5D_4波段（488 nm）的吸收带，无论在不存在二苯甲酮或萘的情况下，都能产生寿命为2.4 ms的单指数发射衰减。吸附在沸石上的芳香族分子的晶间迁移和由此产生的光化学反应的视觉和光谱演示：我们应用荧光显微方法研究了吸附在faujasite沸石上的芳香族分子的晶间迁移。利用由特定电荷补偿阳离子辅助的系统间交叉和能量转移等光物理过程，以及包含在沸石中的客体物种之间的电荷转移（CT）和三重态-三重态能量转移等光化学反应作为指示反应，为单个沸石颗粒提供发光颜色特征。在60 ~ 120℃的温度下加热样品，证明了两种类型的迁移机制：分离沸石晶体之间的空间扩散转移模式和从负载晶体到另一个未负载晶体的分子注入过程，两者都处于接触状态。发现在少数情况下存在客体迁移的优先方向：例如，萘、菲和蒽等芳烃从钠形式的沸石X （Na^+-X）迁移到铊交换的沸石X （Tl^+-X）。另一方面，在给予电子的芳烃（如菲和蒽）和接受电子的1,2,4,5-四苯基苯之间，由于供体的迁移而形成CT配合物，这两种配合物都被纳入单独的沸石Na^+-X晶体中。少

1. A kinetic study on energy transfer between guest aromatic species and rare earth charge-compensating cations within zeolites :The real-time observation is made of energy transfer (ET) between guest aromatic species, benzophenone and naphthalene, and a rare-earth charge compensating cation, Tb^<3+> within a faujasite zeolite Y by the measurement of a time-dependent rise and decay of emission from the ^5D_4 excited-state of Tb^<3+> on excitation of the guest molecules with a pulsed-laser light. Confinement of the guest species within the cages leads to a greatly enhanced emission intensity relative to solution systems, thus facilitating the ET by enforcing the formation of excited-state complexes. Besides, the kinetic behavior of the emission reveals that while benzophenone molecules are immobilized at the protonic sites within the cages, naphthalene molecules are still mobile leading to a remarkable observation of the loading-dependent rise and decay of the Tb^<3+> emission. Consiste … More nt with the assumption of the excited-state complex, a direct excitation of the absorption band of ^7F_6→^5D_4 band (488 nm) of Tb^<3+> results in a single-exponential emission decay with a lifetime of 2.4 ms both in the absence and in the presence of benzophenone or naphthalene.2. Visual and spectroscopic demonstration of intercrystalline migration and resultant photochemical reactions of aromatic molecules adsorbed in zeolites :We applied a fluorescence microscopic method to investigate the intercrystalline migration of aromatic molecules adsorbed in faujasite zeolites. Photophysical processes such as intersystem crossing and energy transfer assisted by particular charge compensating cations, and photochemical reactions such as charge transfer (CT) and triplet-triplet energy transfer between guest species incorporated in the zeolites were exploited as indicator reactions to afford luminescence color characteristic to an individual zeolite particle. Two types of migration mechanism were evidenced assisted by sample heating at temperatures between 60 and 120℃ : a through space diffusional transfer mode between separated zeolite crystals and a molecular injection process from a loaded crystal to another unloaded crystal, both in contact. A preferential direction of guest migration was found to exist for a few cases : for instance, aromatics such as naphthalene, phenanthrene and chrysene migrate from sodium form of zeolite X (Na^+-X) to thallium-exchanged zeolite X (Tl^+-X). On the other hand, the migration-assisted formation of CT complexes between electron-donating arenes such as phenanthrene and chrysene, and electron-accepting 1,2,4,5-tetracyanobenzene, both incorporated into separate zeolite Na^+-X crystals, takes place as a result of the migration of the donors. Less