A transformation process and mechanism between the α-conformation and β-conformation of conjugated polymer PFO in precursor solution

Abstract

In this work, the solvent field and temperature are used to explore the mutual transformation dynamic process and mechanism between the α-conformation and β-conformation in poly(9,9-dioctylfluorene) (PFO) precursor solution. The conformational transformation of the PFO chain is researched by UV-vis absorption spectra and the proportions of the β-conformation are quantitatively calculated. The corresponding variation trend of the aggregation structure is researched using a static and dynamic light scattering (SLS/DLS) method. It is found that the mutual transformation processes between the α-conformation and β-conformation are reversible in essence. Especially in the transformation processes, the complicated relationship between the β-conformation and the aggregation structure is understood, that is the aggregation structure promotes formation of the β-conformation under solvent field, then the conformational transformation of the β-conformation promotes the dissociation of the aggregation structure under temperature. The above results give an insight into the β-conformation and the aggregation structure of PFO in theory. Furthermore, under the temperature, we find that both two transformation steps have good linear correlations, which indicates that using temperature can be considered as a good method to accurately control the proportion of β-conformation in actual applications, and it will help us to get the desired proportion of the β-conformation in PFO precursor solution so as to make the charge carrier mobility of optoelectronic films increased and device performance better.

Single-Molecule Spectroscopy of Polyfluorene Chains Reveals β-Phase Content and Phase Reversibility in Organic Solvents

“…23 It was found that the b phase arises following a two-step process that is initiated by the formation of intrachain planar conformations that subsequently trigger an intermolecular aggregation process. 23,24 The use of single-molecule spectroscopy (SMS), with its unique ability to investigate polymer chains one by one, [25][26][27] has been particularly useful for the study of PFO because its intrinsic phase heterogeneity cannot be resolved by conventional ensemble-averaging spectroscopy. 25,[28][29][30] SMS studies of PFO molecules dispersed in a Zeonex matrix demonstrated the coexistence of aand b-phase chains at 5 K. 31 Considering the highly diluted nature of the samples used in these studies, it was concluded that b-phase formation does not need interchain interactions and that stress-induced backbone planarization could result from interactions with the host matrix.…”

Different phase-dominated chiral assembly of polyfluorenes induced by chiral solvation: axial and supramolecular chirality

“…Studies have shown that the formation mechanism of β phase is divided into two steps. 46 The first step is the energy storage process. The poor solvent reduces the interaction between the PF chains and the good solvent, and increases the force between the PF chains, which causes the formation of aggregates.…”

“…Actually, the α phase indicates that the dihedral angle between adjacent fluorene units is 135°, while the β phase describes a much more coplanar structure with a torsion angle of 165°. 46 The backbone of β phase has a high degree of order, which results in a longer effective conjugation length. 47 The different properties of α and β phase may result in different chiral assembly mechanisms.…”

Small Change, Big Impact: The Shape of Precursor Polymers Governs Poly-p-phenylene Synthesis

“…Although precursor polymers anti -1b and syn -1 show similar absorption maxima at 271 and 269 nm before thermal treatment (Figure ), after aromatization at 300 °C for 10 min (to ensure comparability), PPP anti revealed an absorption maximum at 360 nm and PPP syn at 350 nm. We attribute this red shift to better intra- and interchain interactions of the phenylene units, a phenomenon observed also for other poly-conjugated π-systems with different degrees of order such as poly- p -phenylenevinylene or polythiophenes, − most likely caused by less torsion in the para -phenylene backbone formed from anti -1b . This is plausible since the precursor polymer adopts a similar rigid geometry in comparison to PPP due to anti-connectivity in contrast to the more coiled syn -1 .…”