Multi-level Self-assembly of Conjugated Polymers

Conjugated polymer materials have properties of light-weight, flexibility, good solution processability, performance tunability and low manufacturing cost. Therefore they hold great promise in various applications like light-emitting diodes, photovoltaics, field effect transistors and sensors. Due to the weak intermolecular interactions between conjugated polymers, subtle chemical structure modification and fabrication process alteration will cause variation of molecule assembly behaviours at a broad range of length scale and change of device performance. Thus, complex and diverse multi-level self-assembly structures of conjugated polymers can be formed. This provides rational molecular design and future industrial application with theoretical basis and applicable design strategies. This also sheds light on understanding the "structure-function relationships" of conjugated polymer materials. For the first time, based on systematic comparison of similarity between multi-level self-assembly behaviours of conjugated polymers and proteins, this review proposes that the assemblies used in optoelectronic devices usually have quaternary structures as in proteins: the primary structure is the one-dimensional polymer chain connected by covalent bonding; the secondary structure is multiple polymer chain aggregates forming through interchain interactions like lamellar packing, pi-pi stacking and chain entanglement; the tertiary structure is the phase behaviour as crystalline and amorphous region with domain size and grain boundary; the quaternary structure is the phase segregation in multi-component mixture through interaction between different component and phase interfacial properties. Multi-level self-assembly behaviours are in concert with each other to functionalize conjugated polymer materials by light, electric, magnet and heat performances. This review summarizes recent progresses on studies of conjugated polymer multi-level self-assembly process, which provides us with a new prospect of better observing, understanding and guiding the conjugated polymer multi-level self-assembly process. And thereby the substantial relationship between chemical structure, fabrication processing, assembly behaviour and macroscopic physical process is established, and the optoelectronic properties of polymer materials is furthermore optimized.