Influence of molecular weight and the change of solvent solubility on β conformation and chains condensed state structure for poly (9,9-dioctylfluorene) (PFO) in solution

Chain structure and β conformation of poly(9,9-dioctylfluorene) (PFO) with different molecular weights delivering from the solution to the film in a drop-casting process

“…Currently, there are two main views on the formation of b conformation. In our previous study, 31,32 we found that the self-folding of molecular chains of PFO in the solution was the main reason for the formation of b conformation, which was also supported by Cone's report from the aspect of molecular weight. 46 Conversely, Nagai et al found that the b conformation of polydiarylfluorene (PODPF, another type of polyfluorene) tended to be formed at lower molecular weight because of the interchain interaction.…”

“…44 The contour length of the PFO chains (from M1 to M5) was much longer than the persistent length and it became longer with the increase of molecular weight, which indicated that the shape of single-chain became more and more flexible. In our previous results, 31,32 the value of R g /R h was 2.71-2.46 in good solvent chloroform (M w : 47 000-145 000 Da), and the value of R g /R h was 2.38-2.09 in moderate solvent toluene (M w : 10 700-125 000 Da). Herein, the value of R g /R h was up to 8.9-3.3 in good solvent THF (M w : 25 100-117 000 Da).…”

“…According to previous studies, 31,32,40 in good solvent chloroform and moderate solvent toluene, the PFO single-chain had an extended rod-like structure whose flexibility increased with the increase in molecular weight. We wonder what the single-chain conformation will be like and the differences in THF.…”

“…3a according to the previously reported calculation method. 31,32,40 Similarly, with the increase in molecular weight, the b content increased from 0% to 41% (M1 to M4) and then decreased to 33% (M5).…”

“…From a micro-level perspective, molecular weight and polydispersity index (PDI) can impact device performance (such as carrier mobility and power conversion efficiency) by influencing the solubility, crystallinity, phase transition behaviors, and morphology of the polymers in solutions and films. [28][29][30][31][32] Small changes in the molecular weight can dramatically alter the solution properties, film morphology, and the orderliness of the films. [33][34][35] Therefore, it is important to study the transfer process of chaincondensed structures and ordered conformation of PFO from the solution to the film from the perspective of molecular weight.…”