Effect of Solvent on the Solution State of Conjugated Polymer P7DPF Including Single-Chain to Aggregated State Structure Formation, Dynamic Evolution, and Related Mechanisms

The effect of solvent on the bulky polydiarylfluorene poly[4-(n-alkoxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(n-alkoxy)-9,9-diphenylfluoren-2,7-diyl] (P7DPF) solution state including single-chain to aggregated structure formation, dynamic evolution, and related mechanism was investigated by static/dynamic laser light scattering (DLS/SLS), UV absorption spectroscopy, transmission electron microscopy (TEM), and so on. It was found that solvent had a great influence on the formation of P7DPF beta conformation and aggregation state structure. P7DPF aggregation could be well dissolved into single chains (alpha conformation) in a good solvent (chloroform). But in a relatively poor solvent (toluene), only the alpha conformation was dissolved; the beta conformation could stably exist in the aggregation with size about 100 nm even after being heated at a high temperature (343 K) and ultrasonic oscillation. Interestingly, in the mixed solution of adding different ratio chloroform into toluene solution, although the size of aggregation was unchanged before adding 40% chloroform, the size was dramatically dropped after adding 50% chloroform. In this process, the content of the beta conformation, interchain packing density, and chain orderliness in aggregation were gradually reduced. Those results suggested that solvent can greatly impact chain aggregated structure formation and dynamic evolution. The related mechanism was revealed. The research is of great significance not only to understand the correlation among solvent/P7DPF chains interaction, solution behavior, and device performance but also to understand the physical essence of enhancing photoelectric performance to well control conjugated polymer condensed state structure in application for conjugated polymer-based film optoelectronic devices. The obtained conclusions can help to understand other conjugated polymer systems.