Gold-decorated chiral macroporous films by the self-assembly of functionalised block copolymers

We describe a new and very versatile method to place chosen chemical functionalities at the edge of the pores of macroporous materials. The method is based on the synthesis and self-assembly of inorganic block copolymers (BCPs) having chiral rigid segments bearing controllable quantities of randomly distributed functional groups. The synthesis of a series of optically active block copolyphosphazenes (PP) with the general formula [N=P(R-O2C20H12)(0.9)(FG)(0.2)]n-b-[N=PMePh]m (FG=-OC5H4N (6), -NC4H8S (7), and -NC4H8O (8)), was accomplished by the sequential living cationic polycondensation of N-silylphosphoranimines, using the mono-end-capped initiator [Ph3P=N=PCl3][Cl] (3). The self-assembly of the phosphazene BCPs 6-8 led to chiral porous films. The functionality present on those polymers affected their self-assembly behaviour resulting in the formation of pores of different diameters (D(n)=111 (6), 53 (7) and 77 nm (8)). The specific functionalisation of the pores was proven by decorating the films with gold nanoparticles (AuNPs). Thus, the BCPs 6 and 7, having pyridine and thiomorpholine groups, respectively, were treated with HAuCl4, followed by reduction with NaBH4, yielding a new type of block copolyphosphazenes, which self-assembled into chiral porous films specifically decorated with AuNPs at the edge of the pores.