Slow Energy Transfer in Self‐Doped β‐Conformation Film of Steric Polydiarylfluorenes toward Stable Dual Deep‐Blue Amplified Spontaneous Emission

Abstract

Exciton behavior is crucial for improving the optoelectronic property of a light‐emitting conjugated polymer. Herein, the photoexcitation dynamics of exciton migration and energy transfer in a self‐doped β‐conformation film of the polydiarylfluorenes (poly[4‐(octyloxy)‐9,9‐diphenylfluoren‐2,7‐diyl]‐co‐[5‐(octyloxy)‐9,9‐ diphenylfluoren‐2,7‐diyl], PODPF) are demonstrated. Compared to the first generation of the β‐conformation polyfluorene, poly(9,9‐dioctylfluorene) (PFO), energy transfer occurs in PODPF β‐conformation films in a time period of ≈150 ps, much longer than those of the PFO ones (<5 ps), associated with the effective intrachain energy transfer (few hundred picoseconds), rather than interchain Förster energy transfer (a few picoseconds). Similar to PFO, the PODPF β‐conformation also displays well‐resolved vibronic emission peaks at 20 K, attributed to the planar and rigid conformation. Interestingly, a residual 0‐0 band emission of nonplanar conformation chain segments (435 nm, 2.85 eV) at 20 K also further confirms the exciton migration from the amorphous state to the β‐conformation domain in PODPF films. Therefore, the stable dual amplified spontaneous emission (ASE) behavior of the PODPF self‐doped films at 461 nm (2.69 eV) and 483 nm (2.57 eV), originates from the individual amorphous and β‐conformation domains.

Poly(diarylfluorene) Deep-Blue Polymer Light-Emitting Diodes Based on Submicrometer-Scale Morphological Films Induced by Trace β-Conformation

“…In this regard, the SVA method is a convenient and universal post-processing technology to simultaneously induce the formation of a submicrometer-scale structure on the surface and inside the film (SVA film). Finally, similar to the previous studies, , thermal annealing (TA) is a robust treatment method to cause interchain self-adjustment and obtain the crystalline structure of LCPs. According to the discussion given above, after TA at >220 °C (higher than its T g temperature), highly crystalline PODPF films (TA film) with a high fraction of β-conformational segments are obtained, which are negative for the deep-blue emission. , Therefore, moderate thermal treatment at 210 °C is selected here to induce the formation of trace β-conformation and weak interchain crystallization (Scheme c).…”

“…According to the discussion given above, after TA at >220 °C (higher than its T g temperature), highly crystalline PODPF films (TA film) with a high fraction of β-conformational segments are obtained, which are negative for the deepblue emission. 60,61 Therefore, moderate thermal treatment at 210 °C is selected here to induce the formation of trace βconformation and weak interchain crystallization (Scheme 1c). Finally, a series of submicrometer-scale morphological PODPF films are prepared via controlling the self-assembly behavior in solution and film states (Scheme 1).…”

“…More interestingly, the β-conformation-containing domain of the PDAF film exhibits high deep-blue emission spectral stability, excellent device performance, and stable lasing behavior. ,,,,− However, PDAFs had the inherent drawback poor environmental stability (oxidation), in which the generation of ketone defects was bad for the color purification and the lifetime of the PLEDs. − Fortunately, poly­(diarylfluorene) (typical PODPF materials) with excellent chemical stability and efficient emission was demonstrated in 2014s, which showed diverse self-assembly behaviors, conformational transition, and crystalline capacity in various states . Similar to the PDAF materials, PODPF chains also exhibited the planar (β) conformation state in solid states, which can improve the efficiency and stability of deep-blue emission. − However, the feature of deep-blue emission behavior from the β-conformation can be obtained in the annealed film of PODPF with a high fraction of >20%, where the high degree of crystallization might cause weak interchain π–electron coupling . Meanwhile, compared to the intensity of the 0–0 emission at 453 nm, the strong intensity of the 0–1 emission at 483 nm reduced the deep-blue color purity of PODPF-based light-emitting devices .…”

“…56−60 However, the feature of deep-blue emission behavior from the βconformation can be obtained in the annealed film of PODPF with a high fraction of >20%, where the high degree of crystallization might cause weak interchain π−electron coupling. 61 Meanwhile, compared to the intensity of the 0−0 emission at 453 nm, the strong intensity of the 0−1 emission at 483 nm reduced the deep-blue color purity of PODPF-based light-emitting devices. 58 Therefore, the balance of the βconformation and amorphous state, submicrometer-scale structures, and emission property are the prerequisites to obtain stable deep-blue PLEDs with excellent performance.…”

Solubility Determination and Modeling of 9,9-Dihexyl-2,7-dibromofluorene in Twelve Solvent Systems at 283.15–323.15 K

“…Polyfluorenes (PFs) are a kind of blue light-emitting materials with excellent properties. 1,2 PFs with wide band gaps, excellent thermal and chemical stability, and high quantum efficiency are garnering an increasing amount of research interest. 3,4 In particular, studies on 9,9-disubstituted fluorene-based polymers have demonstrated that such PF derivatives can effectively enhance the solubility and processability of PFs.…”