New 3D supramolecular Zn(ii)-coordinated self-assembled organic networks

Abstract

New 3D supramolecular networks S1 and S2 were prepared by Zn(II) coordination of the tetraphenylmethane-based p-type and n-type molecules bearing four terpyridine ligands. XRD and BET results indicate they are relatively amorphous and non-porous with a high degree of interpenetration within the networks. These could be disassembled by adding more Zn(II) ions and reassembled to form extended 3D networks S3-6 by inserting linear n-type or p-type linking units. BET data suggests that these expanded networks are more porous than the original networks S1-2, but the low porosity and surface area suggest a high degree of interpenetration remains within the expanded networks. The optical properties of these materials were compared to the linear polymers P1-3 made by Zn(II)-mediated assembly of the same linear linking units. The emission spectra of both the 3-D and 1-D cases with the same linking unit matched each other, confirming the incorporation of the linker units into the expanded assemblies. This shows that metal-ligand mediated self-assembly can be used to make two component systems in which the optical properties can be tuned by selection of the units. The assembly was also performed in the presence of CdSe nanocrystals to form nanocomposites.

Self‐Assembly of Conjugated Units Using Metal‐Terpyridine Coordination

“…Addition of two equivalents of either 4 or 5 gave insoluble‐extended networks S3 – S6 . The incorporation of the linear units could be easily detected as the colors were different from parent networks S1 and S2 and their fluorescence matched that of the polymers P1 and P2 containing the same linear units . It should be noted that the structures drawn for S1–S6 are idealized, as the characterization data discussed below suggest the presence of defects.…”

“…The building units for linear 1D polymers were linear oligomers 1 (Figure ) with two terminal tpy units. The core units ( 2 ) for synthesizing our 2D networks were made from 1,3,5‐tri‐(4‐iodophenyl)‐benzene, while the core units ( 3 ) for the 3D networks were prepared from tetrakis(4‐iodophenyl)methane . Attaching linear‐conjugated units with terminal‐coordination bonding motifs (terpyridine, tpy) to the iodoaromatics by Suzuki coupling provided the core molecules for supramolecular self‐assembly.…”

“…We first reported the synthesis of the homopolymers P1 and P2 made from the p‐type unit 4 and n‐type unit 5 . These units are linear and so naturally form linear polymers.…”

“…We have also prepared copolymers P5 – P7 containing both large bandgap energy and/or electron‐donating units 4–7 with the low bandgap energy and/or electron‐accepting unit 8 , in order to study possible energy and/or electron‐transfer processes within them . P5 was formed in a stepwise fashion by breaking up the homopolymer P1 by addition of an equivalent of zinc ions, followed by adding the second monomer 8 .…”

“…For the 3D networks, we made tetrahedral materials (Figure ) with p‐type ( 9 ) and n‐type ( 10 ) arms . Treatment of these with two equivalents of Zn 2+ ions produced insoluble networks S1 and S2 , respectively (Figure ).…”