Directed Assembly of Hierarchical Supramolecular Block Copolymers: A Strategy To Create Donor−Acceptor Charge-Transfer Stacks

Abstract

The hierarchical self-assembly of the charge-transfer (CT) complexes in the solid state is of paramount importance to dictate the performance of electronic devices. In this work, we describe a three-component hierarchical self-assembly approach to generate stable alternate donor–acceptor (D–A) assemblies within block copolymer microdomains by involving the supramolecular approach in self-assembly of block copolymers. So far, the assembly between a single small molecule and block copolymer was explored to obtain block copolymer supramolecules. Here we report block copolymer supramolecules composed of two small molecules (donor and acceptor) and polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP). 1-Pyrenebutyric acid (PBA, donor) forms hydrogen bonding with P4VP and aromatic interactions with naphthalene diimide (NDI, acceptor) to generate CT complexes within the block copolymer domains in the solid state. Using FTIR, SAXS, WAXS, TEM, UV/vis spectroscopy, and photoluminescence spectroscopy measurements, we demonstrate the formation of hierarchical structures and CT complexes between PBA and NDI. Space charge limited current analysis showed the enhanced charge carrier mobility in PS-b-P4VP (PBA+NDI) supramolecules compared to that in the physical blends of PBA+NDI. The organization of donor and acceptor molecules within the block copolymer microdomains opens up new insight into the area of electronic devices because of its advantages such as solution processability, controlled formation of hierarchical assemblies, and the CT interaction in the solid state.