Porphyrin Boxes: Rationally Designed Porous Organic Cages

Abstract

The porphyrin boxes (PB‐1 and PB‐2), which are rationally designed porous organic cages with a large cavity using well‐defined and rigid 3‐connected triangular and 4‐connected square shaped building units are reported. PB‐1 has a cavity as large as 1.95 nm in diameter and shows high chemical stability in a broad pH range (4.8 to 13) in aqueous media. The crystalline nature as well as cavity structure of the shape‐persistent organic cage crystals were intact even after complete removal of guest molecules, leading to one of the highest surface areas (1370 m2g−1) among the known porous organic molecular solids. The size of the cavities and windows of the porous organic cages can be modulated using different sized building units while maintaining the topology of the cages, as illustrated with PB‐2. Interestingly, PB‐2 crystals showed unusual N2 sorption isotherms as well as high selectivity for CO2 over N2 and CH4 (201 and 47.9, respectively at 273 K at 1 bar).

Imine‐Linked Covalent Organic Cage Porous Crystals for CO2 Adsorption

“…They have demonstrated that the interior polar hydroxyl (–OH) groups influence the CO 2 adsorption capacity of the cage. Hong and co‐workers developed wide verity of porphyrin based molecular cage and showed ∼ 200 selectivity for CO 2 separation from flue gas (CO 2 : N 2 ; 15:85 molar ratio) composition . Cooper et al .…”

“…However, the structure and its connectivity are strongly influenced by steric groups presents to the cage vertices in the COC . In the recent years, intensive research activity has been focused on the development of COC molecules with different morphology such as tetrahedral triangular bipyramid, prismatic, prism, trigonal prismatic and prism, barrel, box and adamantoid . The structure, porosity and functional groups present in the cage influences its performance during applications.…”

“…In last few decades, wide varieties of porous materials like Zeolites, porous carbons, ordered mesoporous silica's (OMS's), metal‐organic frameworks (MOFs), porous organic materials and metal‐organic polyhedral have been developed. Among these porous materials, crystals of covalent organic cage (COC) molecules with porosity is also attracting attention in CO 2 adsorption, including energy storage, chiral separation and sensing for its inherent porosity, high specific surface area, low densities, solubility in various solvents and ease of functional group transformation. In addition to the internal porosity, certain functional groups C≡C, C=N, C–N and N–H which are CO 2 ‐philic in nature have play major role during CO 2 adsorption …”

Photophysical properties of porphyrinic covalent cages endowed with different flexible linkers

“…Among the different possibilities in the design of molecular cages, the choice of metallated or freebase porphyrins leads to attractive architectures due to their chemical stability and their mimicry of natural chromophores [1,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Indeed, conversion of light energy into chemical energy performed in photosynthesis relies on efficient multistep energy transfer processes between natural chromophores belonging to the family of porphyrin derivatives (chlorophyll or bacteriochlorophyll molecules) organized in antennas that convey the energy towards the reaction center where the first electron transfer step towards a free-base porphyrin derivative occurs [21][22][23][24][25][26][27].…”

Cucurbitimines – imine cages with concave walls

“…[1][2][3][4][5][6] Although a few examples of boronic ester cages, or those based on disulphide formation or other DCC reactions are known, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] no doubt, the vast majority of shape-persistent organic cages is relying on the use of multiple imine condensation reactions, 1 which bear the advantage to be transformed further to convert these to chemically robust cages, [27][28][29][30][31] which is for the other type of DCC reactions difficult or even impossible. 32 Among those imine cages, shapes, such as trigonal prisms, [33][34][35] tetrahedra, [36][37][38][39] truncated tetrahedra, 40,41 cubes, [42][43][44][45][46] tetrapods,…”