Comprehensive photophysical studies of polyfluorenes containing on-chain emissive defects

Gadermaier, Christoph; Romaner, Lorenz; Piok, Thomas; List, Emil; Souharce, Benjamin; Scherf, Ullrich; Cerullo, Giulio; Lanzani, Guglielmo

doi:10.1103/physrevb.72.045208

Cited by 22 publications

(28 citation statements)

References 26 publications

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“…[24,26] Clearly, at 0.5 ps singlet excitons and polaronpairs coexist, confirming impulsivelike polaron photogeneration. [24,29,30,37] At 8 and 16 ps delays the overall ΔA magnitude decreases but can still be fitted to PA p , PA s , and SE components. At 16 ps PA p ΔA (565 nm) = 0.58 × 10 −2 , PA s ΔA (690 nm) = 0.46 × 10 −2 , and SE ΔA (518 nm) = −0.12 × 10 −2 .…”

Section: Pump-probe Transient Spectroscopy Of Host Materials and Blendsmentioning

confidence: 97%

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Host Exciton Confinement for Enhanced Förster‐Transfer‐Blend Gain Media Yielding Highly Efficient Yellow‐Green Lasers

Zhang

Liu

Wei

et al. 2018

Adv Funct Materials

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This paper reports state-of-the-art fluorene-based yellow-green conjugated polymer blend gain media using Förster resonant-energy-transfer from novel blue-emitting hosts to yield low threshold (≤7 kW cm −2 ) lasers operating between 540 and 590 nm. For poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) (15 wt%) blended with the newly synthesized 3,6-bis(2,7-di([1,1′-biphenyl]-4-yl)-9-phenyl-9H-fluoren-9-yl)-9-octyl-9H-carbazole (DBPhFCz) a highly desirable more than four times increase (relative to F8BT) in net optical gain to 90 cm −1 and 34 times reduction in amplified spontaneous emission threshold to 3 µJ cm −2 is achieved. Detailed transient absorption studies confirm effective exciton confinement with consequent diffusionlimited polaron-pair generation for DBPhFCz. This delays formation of host photoinduced absorption long enough to enable build-up of the spectrally overlapped, guest optical gain, and resolves a longstanding issue for conjugated polymer photonics. The comprehensive study further establishes that limiting host conjugation length is a key factor therein, with 9,9-dialkylfluorene trimers also suitable hosts for F8BT but not pentamers, heptamers, or polymers. It is additionally demonstrated that the host highest occupied and lowest unoccupied molecular orbitals can be tuned independently from the guest gain properties. This provides the tantalizing prospect of enhanced electron and hole injection and transport without endangering efficient optical gain; a scenario of great interest for electrically pumped amplifiers and lasers.

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Section: Pump-probe Transient Spectroscopy Of Host Materials and Blendsmentioning

confidence: 97%

“…Figure 2d,e displays the extracted N pp (t) values from t = 400 fs to 200 ps for PFO and DBPhFCz. Since phenylenepolymer polaronpair generation is intensity dependent, [37] we compared measurements at both low ((d); 80 nJ pulse −1 /66 µJ cm ) and high ((e); 400 nJ pulse…”

Section: Pump-probe Transient Spectroscopy Of Host Materials and Blendsmentioning

confidence: 99%

Host Exciton Confinement for Enhanced Förster‐Transfer‐Blend Gain Media Yielding Highly Efficient Yellow‐Green Lasers

Zhang

Liu

Wei

et al. 2018

Adv Funct Materials

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“…Although the lowest energy transition in fluorenones possesses n-p* character, there is a charge-transfer pp* transition of similar energy. [36,43,52,53] Relaxation from this charge-transfer state has been proposed to be the origin of the green emission. Since the fluorenone defects possess lower transition energies than fluorenes, energy transfer from the dominant fluorene components can be highly favored and occur rapidly prior to fluorene radiative decay.…”

Section: Introductionmentioning

confidence: 99%

Single‐Molecule Studies of a Model Fluorenone

et al. 2007

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Single-molecule fluorescence measurements of 2,7-bis(3,4,5-trimethoxyphenylethenyl)fluorenone (OFOPV) reveal narrow emission spectra concentrated around 540 nm, with weak emission at longer wavelengths. The wide scattering of emission-maximum wavelengths is attributed to varying molecular environments, with dimers or higher-order aggregates contributing to the low-energy emission. This spectral distribution indicates that emission from monomers of this model fluorenone is mostly green, which is consistent with contaminant emission (g-bands) often observed in fluorene- and polyfluorene-based organic light emitting diode (OLED) devices. A histogram of center wavelengths from 118 single-molecule spectra shows good agreement with the green emission previously observed in thermally stressed 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethylfluorene (OFPV). Whereas bulk OFPV exhibits blue fluorescence at about 480 nm, OFOPV bulk thin film measurements reveal red luminescence shifted to 630 nm. This unexpected peak position for bulk OFOPV shifts to higher energies (ca. 540 nm) upon dilution in a solid-state matrix, suggesting that the bulk red emission finds its origins in interactions between fluorenone molecules. Explanations for this red emission include aggregate or excimer formation or intermolecular energy transfer between fluorenone molecules.

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“…4,[22][23][24][25][26][27] Though the true origin of g-band (from fluorenone defect or fluorenone-based excimer) in the PF is not still clear, it is documented that the origin of gband is related to the occurrence of the fluorenone. 8,15,17,[28][29][30] Therefore, a model molecule that is a copolymer of fluorene and fluorenone had been used to clarify the green emission in polyfluorene and the mechanism of fluorenone defect was proposed. 8 But the occurrence of fluorenone segment (without alkyl substituent groups) in copolymer may allow the approach of aromatic groups to distance of 0.3 nm for excimer formation.…”

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confidence: 99%

Studies of Green Emission in Polyfluorenes Using a Model Polymer

et al. 2007

Polym J

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ABSTRACT:The green emission (g-band) in polyfluorene-based conjugated materials is studied by various spectroscopic methods on defined poly(9,9 0 -dioctylfluorene) with one foluorenone unit (P 20 ), which can be seen as a model compound for polyfluorene emitting g-band. The absorption and emission properties of P 20 in the film and solution (room temperature) reveal the optical properties of the green emission emerging in polyfluorene-type polymer. All the experimental evidence obtained demonstrates that g-band in polyfluorene is attributed to the mono-chain fluorenone; and the aggregation of the chains further suppresses the blue emission and enhances g-band.[doi:10.1295/polymj.PJ2007041] KEY WORDS Polyfluorene / Conjugated Polymer / Membrane / Green Emission / Conjugated polymers serving as emitters in lightemitting diodes (LEDs) are attractive to the display industry because of their potential ability for easy and cost-effective processing by solution casting, excellent mechanical properties and structure controllability to tune electro-and photophysical properties.

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Comprehensive photophysical studies of polyfluorenes containing on-chain emissive defects

Cited by 22 publications

References 26 publications

Host Exciton Confinement for Enhanced Förster‐Transfer‐Blend Gain Media Yielding Highly Efficient Yellow‐Green Lasers

Host Exciton Confinement for Enhanced Förster‐Transfer‐Blend Gain Media Yielding Highly Efficient Yellow‐Green Lasers

Single‐Molecule Studies of a Model Fluorenone

Studies of Green Emission in Polyfluorenes Using a Model Polymer

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