Covalently-linked polymers Two-dimensional polymer

figure 2. surface-mediated 2d polymerization scheme of tetrafunctional porphyrin monomer.

two dimensional covalent organic frameworks (cofs) 1 type of microporous coordination polymer can fabricated in 2d plane. dimensionality , topology of 2d cofs result both shape of monomers , relative , dimensional orientations of reactive groups. these materials contain desirable properties in fields of materials chemistry including thermal stability, tunable porosity, high specific surface area, , low density of organic material. careful selection of organic building units, long range π-orbital overlap parallel stacking direction of organic frameworks can achieved.

2d polymerization under thermodynamic control (top) versus kinetic control (bottom). solid black lines represent covalent bond formation



synthetic scheme of covalent organic framework using boronic acid , hexahydroxytriphenylene.

many covalent organic frameworks derive topology directionality of covalent linkages, small changes in organic linkers can dramatically affect mechanical , electronic properties. small changes in structure can induce dramatic changes in stacking behavior of molecular semiconductors.

porphyrins additional class of conjugated, heterocyclic macrocycles. control of monomer assembly through covalent assembly has been demonstrated using covalent interactions porphyrins. upon thermal activation of porphyrin building blocks, covalent bonds form create conductive polymer, versatile route bottom-up construction of electronic circuits been demonstrated.

cof synthesis

boronate ester equilibria used prepare various 2d cofs

it possible synthesize cofs using both dynamic covalent , non-covalent chemistry. kinetic approach involves stepwise process of polymerizing pre-assembled 2d-monomer while thermodynamic control exploits reversible covalent chemistry allow simultaneous monomer assembly , polymerization. under thermodynamic control, bond formation , crystallization occur simultaneously. covalent organic frameworks formed dynamic covalent bond formation involves chemical reactions carried out reversibly under conditions of equilibrium control. because formation of cofs in dynamic covalent formation occurs under thermodynamic control, product distributions depend on relative stabilities of final products. covalent assembly form 2d cofs has been done using boronate esters catechol acetonides in presence of lewis acid (bf3*oet2).

2d polymerization under kinetic control relies on non-covalent interactions , monomer assembly prior bond formation. monomers can held in pre-organized position non-covalent interactions, such hydrogen bonding or van der waals.