Solution‐crystallization and related phenomena in 9,9‐dialkyl‐fluorene polymers. I. Crystalline polymer‐solvent compound formation for poly(9,9‐dioctylfluorene)

Aggregates -that is short-ranged ordered moieties in the solid-state of p-conjugated polymers -play an important role in the photophysics and performance of various optoelectronic devices. We have previously shown that many polymers change from a disordered to a more ordered conformation when cooling a solution below a characteristic critical temperature T c . Using in situ time-resolved absorption spectroscopy on the prototypical semiconducting polymers P3HT, PFO, PCPDTBT, and PCE11 (PffBT4T-2OD), we show that spincoating at a temperature below T c can enhance the formation of aggregates with strong intra-chain coupling. An analysis of their time-resolved spectra indicates that the formation of nuclei in the initial stages of film formation for substrates held below T c seems responsible for this. We observe that the growth rate of the aggregates is thermally activated with an energy of 310 meV, which is much more than that of the solvent viscosity (100 meV). From this we conclude that the rate controlling step is the planarization of a chain that is associated with its attachment to a nucleation center. The success of our approach for the rather dynamic deposition method of spin-coating holds promise for other solution-based deposition methods.So far, however, only limited approaches have been reported to induce aggregate formation in a controlled fashion, including slow solidification in marginal solvents, 26-29 control of entanglements and sonication, 30-34 and blending 35 -many using poly(3-hexyl thiophene) (P3HT) as model system and many relying on relatively time-consuming methodologies. Approaches to control the formation of aggregates during the solution deposition should ideally be based on considering thermodynamics of the solution as well as by taking the kinetics of film formation into account. 9 In particular with respect to the latter, several methods have been reported, such as varying the boiling point of the solvent, 9,21,36 varying Additional Supporting Information may be found in the online version of this article.

T_{normalc}

for this transition is near room temperature and, thus, a solution can readily be brought to a temperature above or below

T_{normalc}

as desired.…”

Section: Introductionmentioning

confidence: 99%

Controlling aggregate formation in conjugated polymers by spin‐coating below the critical temperature of the disorder–order transition

Reichenberger

Kroh

Matrone

et al. 2017

“…14,15 In addition to this, the remarkably diverse polymorphism of PFO is also the focus of extensive research effort-both fundamental and application-driven-with its characteristic well-defined b-phase conformational isomer receiving particular attention. 8,9,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] When processed from solutions in good solvents (Hildebrand solubility parameter d 9.2 cal 1/2 cm 23/2 as for, e.g., chloroform or tetrahydrofuran) [16][17][18] that also allow for sufficiently rapid solvent evaporation during film deposition (e.g., toluene heated to 100 8C), 15 in-plane isotropic, "glassy" PFO films are obtained. 34 In such films the PFO chains adopt a range of disordered wormlike conformations, collectively also termed "glassy," featuring a broad distribution of intermonomer torsion angles.…”

mentioning

confidence: 99%

“…The b-phase conformation corresponds to a distinct chain-extended molecular geometry in which the torsion angle between adjacent fluorene units is 1808, resulting in their coplanar orientation, with the octyl substituents located on alternating sides of the backbone. 17,23,29,32 (See inset of Fig. 2 for the chemical structure of PFO and a schematic illustration of its glassy and bphase chain conformations.)…”

mentioning

confidence: 99%

Spectroscopic properties of poly(9,9‐dioctylfluorene) thin films possessing varied fractions of β‐phase chain segments: enhanced photoluminescence efficiency via conformation structuring

Perevedentsev

Chander

Kim

et al. 2016

Self Cite

126

Poly(9,9‐dioctylfluorene) (PFO) is a widely studied blue‐emitting conjugated polymer, the optoelectronic properties of which are strongly affected by the presence of a well‐defined chain‐extended “β‐phase” conformational isomer. In this study, optical and Raman spectroscopy are used to systematically investigate the properties of PFO thin films featuring a varied fraction of β‐phase chain segments. Results show that the photoluminescence quantum efficiency (PLQE) of PFO films is highly sensitive to both the β‐phase fraction and the method by which it was induced. Notably, a PLQE of ∼69% is measured for PFO films possessing a ∼6% β‐phase fraction induced by immersion in solvent/nonsolvent mixtures; this value is substantially higher than the average PLQE of ∼55% recorded for other β‐phase films. Furthermore, a linear relationship is observed between the intensity ratios of selected Raman peaks and the β‐phase fraction determined by commonly used absorption calibrations, suggesting that Raman spectroscopy can be used as an alternative means to quantify the β‐phase fraction. As a specific example, spatial Raman mapping is used to image a mm‐scale β‐phase stripe patterned in a glassy PFO film, with the extracted β‐phase fraction showing excellent agreement with the results of optical spectroscopy. © 2016 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1995–2006

“…Forthcoming studies will concentrate on how the side chain asymmetry influences solution crystallization following the ideas shown for PF8 and PF8-F2/6 copolymers by Bradley, Fujiki, and coworkers 45,46 and those for PF8 by Yan and coworkers 47 -and the formation of freeze-dried xerogels following the ideas shown for PF8 by Xie and coworkers. 48 They should also include the use of selective solvents and crystal growth as demonstrated for PF10 by Fujiki and coworkers 49 ; or nanowires and particles as shown by Redmond, O'Carroll, and coworkers.…”

Section: Discussionmentioning

confidence: 98%

Poly(9‐undecyl‐9‐methyl‐fluorene) and poly(9‐pentadecyl‐9‐methyl‐fluorene): Synthesis, solution structure, and effect of side chain asymmetry on aggregation behavior

Knaapila¹,

Stewart

Garamus

et al. 2019

We report on solution aggregates and backbone conformation of poly(9‐undecyl‐9‐methyl‐fluorene) (PF1‐11) and poly(9‐pentadecyl‐9‐methyl‐fluorene) (PF1‐15), having two different side chains compared with poly(9,9‐dihexylfluorene) (PF6) and poly(9,9‐dioctylfluorene) (PF8) with two identical side chains. In the poor solvent methylcyclohexane (MCH), X‐ray scattering indicates that PF1‐11 and PF1‐15 appear as three‐dimensional aggregates (5–10 nm wide and thick), forming ribbon‐like agglomerates (correlation lengths of 100 nm). PF6 and PF8 appear as two‐dimensional aggregates (>10 nm wide and 2–3 nm thick) involving ribbon‐like agglomerates (correlation lengths much greater than 100 nm). Upon heating, all aggregates undergo a gel–sol transition which occurs at lower temperatures for PF1‐11 and PF1‐15 (<60°C) than for PF6 and PF8 (>80°C). In the good solvent toluene, PF1‐11 and PF1‐15 form networks of cylindrical particles. The mesh size and the cylinder radius are smaller in 24°C toluene (60 nm, 0.5 nm) than in 60°C MCH (300 nm, 1–2 nm). Nuclear magnetic resonance spectra in toluene‐d8 together with density functional theory calculations suggest higher torsion angles between polymer repeat units for PF6, PF8, and PF1‐11 (less planar conformation) and a gauche arrangement of the dihedral angles between the bridge carbon atom and the side chain methylene groups in PF1‐15. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 826–837