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

Abstract

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 β conformation and aggregation state structure. P7DPF aggregation could be well dissolved into single chains (α conformation) in a good solvent (chloroform). But in a relatively poor solvent (toluene), only the α conformation was dissolved; the β 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 β 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.

Correlating Charge Transport Properties of Conjugated Polymers in Solution Aggregates and Thin‐Film Aggregates

“…To provide further insight into the polymer aggregation effects,w ec onducted SANS measurements.T he extracted Porod exponents represented the degree of clustering of polymers in solution. [10] As shown in Figure S5, the Porod exponents increased from FBDOPV-2T to FBDOPV-4F2T. By fitting the ln I(q)-ln q line,the Porod exponents were 0.95 for FBDOPV-2T,1 .14 for FBDOPV-2F2T,a nd 2.07 for FBDOPV-4F2T,respectively.P orod exponents of FBDOPV-2T and FBDOPV-2F2T were close to 1, illustrating that the polymer chain adopted the extended conformation in solution.…”

Origin of the Anisotropy and Structure of Ellipsoidal Poly(fluorene) Nanoparticles

“…Poly(diarylfluorenes) as a materials class were found to meet these demands (Figure 1.5). 39,54 The bulky aryl substituents at the C-9 position had a favorable impact on the chemical and thermal stability of the material, as compared to poly(dialkylfluorenes). 35,39,55 The sensitivity towards oxidation was reduced and the blue-light emission showed improved stability.…”

“…22,56 The functionalization of the original polymer with alkoxy groups in C-5 position led to the induction of β-phase conformation, as observed by various analytical methods. 54,55,57,58 The molecular arrangement was explained by the subtle interplay of steric repulsion of the bulky aryl groups and attractive van-der-Waals forces of the alkoxy substituents. 55 This interplay enabled the planarization of the polymer backbone, comparable to the conformation found in PF8.…”

“…57,58 The formation of β-phase in poly(alkoxy-9,9´-diarylfluorenes) was evident from additional shoulders or peaks in absorption and emission spectra upon preparation of solutions or gels or by film formation via spin-coating. 54,55 Thermal post-processing of spin-coated films on glass substrates exhibited a significant increase in β-phase ratio (up to 45% at 240 °C) upon annealing at elevated temperatures. 57 Based on their molecular attractorrepulsor design, poly(alkoxy-9,9´-diarylfluorenes) constitute conjugated polymers of wide bandgap with high potential for extensive applications in optoelectronics.…”

“…Likewise, the corresponding emission peaks at 427 nm, 449 nm and 489 nm were assignable to amorphous state PODPF by comparison with published literature, while the signals of β-phase conformation remained absent. 39,54,206 It can hence be assumed that the polymer backbone planarization required for the formation of β-phase PODPF in observable quantities involves different requirements than in the case of PF8. Conclusively, under the given reaction conditions, neither the occurrence of β-phase regions in PODPF nor the formation of defined ellipsoidal nanoparticles could be ensured; an effect which applies to both pure PODPF and for the copolymers studied.…”