We report the observation of the smectic A
F
, a liquid crystal phase of the ferroelectric nematic realm. The smectic A
F
is a phase of small polar, rod-shaped molecules that form two-dimensional fluid layers spaced by approximately the mean molecular length. The phase is uniaxial, with the molecular director, the local average long-axis orientation, normal to the layer planes, and ferroelectric, with a spontaneous electric polarization parallel to the director. Polarization measurements indicate almost complete polar ordering of the ∼10 Debye longitudinal molecular dipoles, and hysteretic polarization reversal with a coercive field ∼2 × 10
5
V
/
m is observed. The SmA
F
phase appears upon cooling in two binary mixtures of partially fluorinated mesogens: 2N/DIO, exhibiting a nematic (N)–smectic Z
A
(SmZ
A
)–ferroelectric nematic (N
F
)–SmA
F
phase sequence, and 7N/DIO, exhibiting an N–SmZ
A
–SmA
F
phase sequence. The latter presents an opportunity to study a transition between two smectic phases having orthogonal systems of layers.
De Vries-like materials show small layer shrinkages at the SmA to SmC transition and can therefore be applied in surface-stabilized ferroelectric liquid crystal displays. Here we report the synthesis and...
The use of thermally activated delayed fluorescence (TADF) emitters and emitters that show preferential horizontal orientation of their transition dipole moment (TDM) are two emerging strategies to enhance the efficiency of OLEDs. We present the first example of a liquid crystalline multi-resonance TADF (MR-TADF) emitter, DiKTa-LC. The compound possesses a nematic liquid crystalline phase between 80 °C and 110 °C. Importantly, the TDM of the spin-coated film shows preferential horizontal orientation, with an anisotropy factor, a, of 0.28, which is preserved in doped poly(vinylcarbazole) films. Green-emitting (λ EL = 492 nm) solution-processed OLEDs based on DiKTa-LC showed an EQE max of 13.6 %. We thus demonstrate for the first time how self-assembly of a liquid crystalline TADF emitter can lead to the so-far elusive control of the orientation of the transition dipole in solutionprocessed films, which will be of relevance for highperformance solution-processed OLEDs.
The use of thermally activated delayed fluorescence (TADF) emitters and emitters that show preferential horizontal orientation of their transition dipole moment (TDM) are two emerging strategies to enhance the efficiency of OLEDs. We present the first example of a liquid crystalline multi-resonance TADF (MR-TADF) emitter, DiKTa-LC. The compound possesses a nematic liquid crystalline phase between 80 °C and 110 °C. Importantly, the TDM of the spin-coated film shows preferential horizontal orientation, with an anisotropy factor, a, of 0.28, which is preserved in doped poly(vinylcarbazole) films. Green-emitting (λ EL = 492 nm) solution-processed OLEDs based on DiKTa-LC showed an EQE max of 13.6 %. We thus demonstrate for the first time how self-assembly of a liquid crystalline TADF emitter can lead to the so-far elusive control of the orientation of the transition dipole in solutionprocessed films, which will be of relevance for highperformance solution-processed OLEDs.
The use of thermally activated delayed fluorescence emitters and emitters that show preferential horizontal orientation of their transition dipole are two emerging strategies to enhance the efficiency of organic light-emitting diodes. We present the first example of a liquid crystalline multi-resonance thermally activated delayed fluorescent emitter, DiKTaLC. The neat film of DiKTaLC shows a photoluminescence quantum yield of 41%, a singlet-triplet energy gap, ΔEST, of 0.20 eV, and a delayed lifetime, τd, of 70.2 µs. The compound possesses a nematic discotic liquid crystalline phase between 80 °C and 110 °C. More importantly, the transition dipole moment of the spin-coated film shows preferential horizontal orientation, with an anisotropy factor, a, of 0.26. We thus demonstrate for the first time how self-assembly of a liquid crystalline TADF emitter can lead to the so-far elusive control of the orientation of the transition dipole in solution-processed films, which will be of relevance for high-performance solution-processed organic light-emitting diodes.
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