No abstract

Porosity makes powerful affinity materials for quartz crystal microbalances. The shape-persistent organic cages and pores create superior affinity systems to existing ones for direct tracing of aromatic solvent vapors. A shape and size selectivity for the analytes is observed. These organic cages can be processed to thin films with highly reproducible sensing properties.

The synthesis of various periphery-substituted shape-persistent cage compounds by twelve-fold condensation reactions of four triptycene triamines and six salicyldialdehydes is described, where the substituents systematically vary in bulkiness. The resulting cage compounds were studied as permanent porous material by nitrogen sorption measurements. When the material is amorphous, the steric demand of the cages exterior does not strongly influence the gas uptake, resulting in BET surface areas of approximately 700 m(2)  g(-1) for all cage compounds 3 c-e, independently of the substituents bulkiness. In the crystalline state, materials of the same compounds show a strong interconnection between steric demand of the peripheral substituent and the resulting BET surface area. With increasing bulkiness, the overall BET surface area decreases, for example 1291 m(2)  g(-1) (for cage compound 3 c with methyl substituents), 309 m(2)  g(-1) (for cage compound 3 d with 2-(2-ethyl-pentyl) substituents) and 22 m(2)  g(-1) (for cage compound 3 e with trityl substituents). Furthermore, we found that two different crystalline polymorphs of the cage compound 3 a (with tert-butyl substituents) differ also in nitrogen sorption, resulting in a BET surface area of 1377 m(2) g(-1), when synthesized from THF and 2071 m(2) g(-1), when recrystallized from DMSO.

Interior decorating: A post‐synthetic method allows porous organic cage compounds to be prepared with functionalized interior cavities. The approach produces modified cage compounds in quantitative yield and opens the possibility of preparing organic alloys with different functionality. The solution‐based technique shows the advantage of solubility, an inherent property of porous materials derived from discrete organic molecules.

The bigger the better? Rigidity is more important than size for the construction of permanent porous crystals from organic cage compounds. Two [2+3] cage compounds have been synthesized by an imine condensation reaction. The one consisting of rigid subunits (figure left) has an accessible BET surface area of 744 m2 g−1, whereas the cage compound with flexible subunits is basically nonporous (BET surface area: 30 m2 g−1) although the shape‐persistent cavity is larger (9.8 vs. 7.8 Å).