Correlation between the crystallization of polyfluorene and the surface free energy of substrates

Third-order optical susceptibility of ordered and disordered polyfluorene thin films

“…This order is also confirmed by the peak positions of their photoluminescence, the transition dipole moments of their lowest excited states, and their HuangRhys factors [10,19,20]. Note that the absorption spectrum of the crystalline thin film has shoulders around 3.5 eV as well as at 2.9 eV, and thus appears broader than the others [21]. Although its maximum absorbance appears to be small, oscillator strength in the displayed spectral range is conserved between all three phases.…”

Directional Alignment of Polyfluorene Copolymers at Patterned Solid-Liquid Interfaces

“…Polyfluorene is an efficient light-emitting polymer and its derivatives have been used extensively in light-emitting diodes, transistors, and optically-pumped thin-film lasers [ 16 , 17 , 18 , 19 ]. Although polyfluorene shows small-scale π-stacking phases in some specially prepared solid films, [ 20 , 21 , 22 ] and oriented alignment of poly-9,9-dioctylfluorene (PFO), poly-9,9-dioctylfluorene-co-bethiadisazole (F8BT), and Poly-9,9-dioctylfluorenyl-2,7-diyl-co-bithiophene (F8T2) molecules has been studied on rubbed-polyimide-modified substrates [ 23 ], large-scale or long-range alignment has not been reported in the films of these polymers.…”

An In Situ Investigation into the Formation of the Solvent‐Induced Crystalline Phase of Poly(9,9‐Dioctylfluorene) in Solvent Vapor Annealing

“…[19][20][21][22] Generally speaking, the β phase of PFO can be physically formed by four methods: extending the time of fi lm casting by using high boiling point solvent or an additive in the PFO solution and exposing the PFO thin fi lm to solvent vapor (solvent vapor annealing, using hexane, cyclohexane, tetrahydrofuran, or toluene); [23][24][25][26][27] reducing the solubility of PFO in the solution by dissolving PFO in or immersing the thin fi lm into a mixture of good solvent and non-solvent (e.g., chloroform/methanol); [ 20,[28][29][30][31][32] cooling and reheating PFO thin fi lm to room temperature to promote molecular rearrangement; [ 13,28,30,33 ] tuning the surface free energies of several substrates. [ 34 ] Recently we have developed a new method called solvent vapor assisted spin-coating, which produces an atmosphere of solvent vapor in the spin-coater to directly prepare PFO thin fi lm containing β phase. By means of transmission electron microscopy (TEM) and grazing incidence wide-angle X-ray scattering (GIWAXS), we have demonstrated the presence of a previously unspecifi ed metastable phase of PFO, that is, the crystalline phase.…”

“…A low content of β phase can act as a dopant and lead to efficient energy transfer, more balanced charge flux, and more efficient charge recombination in PFO, which makes PFO a promising candidate for electroluminescence devices with a more pure and stable blue emission . Generally speaking, the β phase of PFO can be physically formed by four methods: extending the time of film casting by using high boiling point solvent or an additive in the PFO solution and exposing the PFO thin film to solvent vapor (solvent vapor annealing, using hexane, cyclohexane, tetrahydrofuran, or toluene); reducing the solubility of PFO in the solution by dissolving PFO in or immersing the thin film into a mixture of good solvent and non‐solvent (e.g., chloroform/methanol); cooling and reheating PFO thin film to room temperature to promote molecular rearrangement; tuning the surface free energies of several substrates . Recently we have developed a new method called solvent vapor assisted spin‐coating, which produces an atmosphere of solvent vapor in the spin‐coater to directly prepare PFO thin film containing β phase.…”