Circularly polarized thermally activated delayed fluorescence (CP‐TADF) and multiple‐resonance thermally activated delayed fluorescence (MR‐TADF), which exhibit novel circularly polarized ...luminescence and excellent color fidelity, respectively, have gained immense popularity. In this study, integrated CP‐TADF and MR‐TADF (CPMR‐TADF) are prepared by strategic design and synthesis of asymmetrical peripherally locked enantiomers, which are separated and denoted as (P,P″,P″)‐/(M,M″,M″)‐BN4 and (P,P″,P″)‐/(M,M″,M″)‐BN5 and exhibit TADF and circularly polarized light (CPL) properties. As the entire molecular frame participates in the frontier molecular orbitals, the resulting helical chirality of (+)/(−)‐BN4‐ and (+)/(−)‐BN5‐based solution‐processed organic light‐emitting diodes (OLEDs) helps in achieving a narrow full width at half maximum (FWHM) of 49/49 and 48/48 nm and a high maximum external quantum efficiency (EQE) of 20.6%/19.0% and 22.0%/26.5%, respectively. Importantly, unambiguous circularly polarized electroluminescence signals with dissymmetry factors (gEL) of +3.7 × 10−3/−3.1 × 10−3 (BN4) and +1.9 × 10−3/−1.6 × 10−3 (BN5) are obtained. The results indicate successful exploitation of CPMR‐TADF‐emitter‐based OLEDs to exhibit three characteristics: high efficiency, color purity, and circularly polarized light.
Circularly polarized thermally activated delayed fluorescence (CP‐TADF) and multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) properties are integrated into a new advanced material, a CPMR‐TADF material. OLEDs based on these CPMR‐TADF emitters show excellent performance, attaining a three‐in‐one advantage: high efficiency, color purity, and circular polarized light simultaneously.
Research into organic light emitters employing multiple resonance-induced thermally activated delayed fluorescence (MR-TADF) materials is presently attracting a great deal of attention due to the ...potential for efficient deep-blue emission. However, the origins and mechanisms of successful TADF are unclear, as many MR-TADF materials do not show TADF behaviour in solution, but only as particular pure solids. Here, an investigation into a well-known MR-TADF material, DABNA-1, together with other new MR materials (9H-quinolino3,2,1-klphenothiazin-9-one (QPO) and 9H-quinolino-3,2,1-kl-phenothiazin-9-one 5,5-dioxide (QP3O)), yields new insights regarding the origin of TADF. Although a material system may support the concept of MR, inefficiency in both forward and reverse intersystem crossings forbids TADF unless a suitable host material allows an exciplex-like host–emitter interaction that boosts TADF. This boosted-TADF mechanism can be generalized to any fluorescence dye that lacks TADF in the photoluminescence measurement but has a thermally accessible S1–T1 energy gap, opening the way to high-performance organic light-emitting diodes.This study reveals the importance of host–guest interactions for effective multiple-resonance thermally activated delayed fluorescence in organic light emitters.
Near‐infrared organic light‐emitting diodes (NIR OLEDs) enable many unique applications ranging from night‐vision displays and photodynamic therapies. However, the development of efficient NIR OLEDs ...with a low efficiency roll‐off is still challenging. Here, a series of new heteroleptic Pt(II) complexes (1–4) flanked by both pyridyl pyrimidinate and functional azolate chelates are synthesized. The reduced ππ* energy gap of the pyridyl pyrimidinate chelate, and strong intermolecular interaction and high crystallinity in vacuum‐deposited thin films engender strong intermolecular charge transfer transition including metal–metal‐to‐ligand charge transfer; thereby, exhibiting efficient photoluminescence within 776–832 nm and short radiative lifetimes of 0.52–0.79 µs. Consequently, nondoped NIR‐emitting OLEDs based on these Pt(II) complexes are fabricated, to which Pt(II) complexes 2 and 4 give record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively. Moreover, low efficiency roll‐off is also observed, among which the device efficiencies of 2 and 4 are at least four times higher than that of the best NIR‐emitting OLEDs recorded at current density of 100 mA cm−2.
Nondoped near‐infrared organic light‐emitting diodes based on pyrimidinate‐pyrazolate Pt(II) metal complexes 2 and 4 are fabricated, yielding a record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively.
In the emerging field of intramolecular charge transfer induced counterion migration, we report the new insights into photophysical features of luminescent donor–acceptor phosphonium dyes (D−π−)nA+X− ...(π=−(C6H4)x−). The unique connectivity of the phosphorus atom affords multipolar molecules with a variable number of arms and the electronic properties of the acceptor group. In the ion‐paired form, the transition from dipolar to quadrupolar configuration enhances the low energy migration‐induced band by providing the additional pathways for anion motion. The multipolar architecture, adjustable lengths of the π‐spacers and the nature of counterions allow for efficient tuning of the emission and achieving nearly pure white light with quantum yields around 30 %. The methyl substituent at the phosphorus atom reduces the rate of ion migration and suppresses the red shifted bands, simultaneously improving total emission intensity. The results unveil the harnessing of the multiple emission of phosphonium fluorophores by anion migration via structure and branching of donor–acceptor arms.
The photophysical properties of a series of multipolar donor–acceptor phosphonium fluorophores (D−π−)nA+X− have been investigated. These dyes exhibit steady‐state panchromatic luminescence attributed to the photoinduced counterion migration. The intra‐ion‐pair dynamics and the fluorescence response can be rationally tuned on the molecular level that might broaden the scope of functionalities and stimulate the development of new ionic systems.
Phosphonium‐based compounds gain attention as promising photofunctional materials. As a contribution to the emerging field, we present a series of donor‐acceptor ionic dyes, which were constructed by ...tailoring phosphonium (A) and extended π‐NR2 (D) fragments to an anthracene framework. The alteration of the π‐spacer of electron‐donating substituents in species with terminal −+PPh2Me groups exhibits a long absorption wavelength up to λabs=527 nm in dichloromethane and shifted the emission to the near‐infrared (NIR) region (λ=805 nm for thienyl aniline donor), although at low quantum yield (Φ<0.01). In turn, the introduction of a P‐heterocyclic acceptor substantially narrowed the optical bandgap and improved the efficiency of fluorescence. In particular, the phospha‐spiro moiety allowed to attain NIR emission (797 nm in dichloromethane) with fluorescence efficiency as high as Φ=0.12. The electron‐accepting property of the phospha‐spiro constituent outperformed that of the monocyclic and terminal phosphonium counterparts, illustrating a promising direction in the design of novel charge‐transfer chromophores.
Low energy absorption and emission were realized in a series of anthracene‐derived donor‐acceptor phosphonium dyes. The electron deficiency of the rare phospha‐spiro architecture allowed to achieve fluorescence at 797 nm in dichloromethane and at 860 nm in the solid state.
In this study, the chromophore 3,4,9,10-perylenetetracarboxylic diimide (PDI) is anchored with phenyl substituents at the imide N site, followed by thionation, yielding a series of thione products ...1S-PDI-D, 2S-cis-PDI-D, 2S-trans-PDI-D, 3S-PDI-D, and 4S-PDI-D, respectively, with n = 1, 2, 3, and 4 thione. The photophysical properties are dependent on the number of anchored thiones, where the observed prominent lower-lying absorption is assigned to the S0 → S2(ππ*) transition and is red-shifted upon increasing the number of thiones; the lowest-lying excited state is ascribed to a transition-forbidden S1(nπ*) configuration. All nS-PDIs are non-emissive in solution but reveal an excellent two-photon absorption cross-section of >800 GM. Supported by the femtosecond transient absorption study, the S1(nπ*) → T1(ππ*) intersystem crossing (ISC) rate is > 1012 s–1, resulting in ∼100% triplet population. The lowest-lying T1(ππ*) energy is calculated to be in the order of 1S-PDI-D > 2S-cis-PDI-D ∼ 2S-trans-PDI-D > 3S-PDI-D > 4S-PDI-D, where the T1 energy of 1S-PDI-D (1.10 eV) is higher than that (0.97 eV) of the 1O2 1Δ g state. 1S-PDI-D is further modified by either conjugation with peptide FC131 on the two terminal sides, forming 1S-FC131, or linkage with peptide FC131 and cyanine5 dye on each terminal, yielding Cy5-1S-FC131. In vitro experiments show power of 1S-FC131 and Cy5-1S-FC131 in recognizing A549 cells out of other three lung normal cells and effective photodynamic therapy. In vivo, both molecular composites demonstrate outstanding antitumor ability in A549 xenografted tumor mice, where Cy5-1S-FC131 shows superiority of simultaneous fluorescence tracking and targeted photodynamic therapy.
Three functional pyrazinyl pyrazolate Pt(II) complexes Pt(fprpz)2 (1), Pt(2fprpz)2 (2), and Pt(5fprpz)2 (3), each with CF3, CF2H, and C2F5 substituents on pyrazolate, were synthesized from ...treatment of Pt(DMSO)2Cl2 and respective pyrazinyl pyrazole chelates (fprpz)H, (2fprpz)H, and (5fprpz)H in refluxing tetrahydrofuran solution. Variations of these fluorinated substituents provided a profound effect on both the photo- and electroluminescence properties of as-prepared Pt(II) metal complexes in solution and solid states, respectively. More specifically, there exists a dominant ligand-centered 3ππ* state contribution in both the solution state and doped thin films at a low concentration, which are strongly dependent upon the nature of the pyrazolate entity and tendency of self-aggregation. A systematic study demonstrates that the T1 state properties can be fine-tuned by altering their functional substituents. Because Pt(II) complex 2 bears the least electron-deficient CF2H substituent, its thin film has shown the longest emissive wavelength in comparison to other derivatives. Upon formation of a vacuum-deposited thin film, the transition of the titled Pt(II) complexes is dominated by metal–metal-to-ligand charge transfer transition that can be tuned by the well-aligned stacking of the Pt(II) complexes, being more delocalized hence decreasing the energy upon increasing the stacking density. Moreover, we fabricated a series of organic light-emitting diodes (OLEDs) in an attempt to probe the concentration dependence of the doped emitter versus device performances. The electroluminescence of Pt(II) complex 1 shifted from sky blue to near infrared as the doping ratio gradually increased from 1 to 100 wt %. Broad-band white emission can also be realized by adjusting the concentration for optimal monomeric and aggregate emissions. With this remarkable feature, a highly efficient white OLED with external quantum efficiency up to 21.4% and spectral coverage from 450 to 800 nm was obtained at the doping level of 10 wt %, representing ideal candidates in developing solid-state lighting luminaries.
Tadf Emitters
Circularly polarized thermally activated delayed fluorescence (CP‐TADF) and multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) properties are integrated into new ...CPMR‐TADF materials by Xiugang Wu, You‐Xuan Zheng, Weiguo Zhu, Pi‐Tai Chou, and co‐workers, as described in article number 2105080. Organic light‐emitting diodes based on these CPMR‐TADF emitters attain a three‐in‐one advantage simultaneously: high efficiency, color purity, and circular polarized light.
In organic and organometallic solids, upon electronic excitation, most intermolecular structural relaxations follow a pathway along the π–π stacking direction or metal–metal bond with significant ...coupling strength. Differently, we discovered that the self-assembled platinum(II) complexes, Pt(fppz) 2 , exhibit an unusual interchain contraction. The ground-state and excited-state multiple local minima were distinguished by temperature-dependent excitation/emission spectra, indicating the existence of multiple local minima. The time-resolved emission decay revealed the excited-state structural relaxation lifetime with τobs = 41 ns at 298 K. Temperature-dependent X-ray diffraction analysis showed that the packing geometries contract 0.6 Å along the interchain direction (a-axis) at 50 K compared to the geometries at 298 K. Such structural displacements render the slow internal conversion rate in the excited states. We thus demonstrate the correlation between the packing geometries and the excited-state dynamics of the self-assembled Pt(II) complexes, shedding light on the unique direction of interchain structural deformation of the molecular aggregates.
In the emerging field of intramolecular charge transfer induced counterion migration, we report the new insights into photophysical features of luminescent donor–acceptor phosphonium dyes (D−π−)nA+X− ...(π=−(C6H4)x−). The unique connectivity of the phosphorus atom affords multipolar molecules with a variable number of arms and the electronic properties of the acceptor group. In the ion‐paired form, the transition from dipolar to quadrupolar configuration enhances the low energy migration‐induced band by providing the additional pathways for anion motion. The multipolar architecture, adjustable lengths of the π‐spacers and the nature of counterions allow for efficient tuning of the emission and achieving nearly pure white light with quantum yields around 30 %. The methyl substituent at the phosphorus atom reduces the rate of ion migration and suppresses the red shifted bands, simultaneously improving total emission intensity. The results unveil the harnessing of the multiple emission of phosphonium fluorophores by anion migration via structure and branching of donor–acceptor arms.
The photophysical properties of a series of multipolar donor–acceptor phosphonium fluorophores (D−π−)nA+X− have been investigated. These dyes exhibit steady‐state panchromatic luminescence attributed to the photoinduced counterion migration. The intra‐ion‐pair dynamics and the fluorescence response can be rationally tuned on the molecular level that might broaden the scope of functionalities and stimulate the development of new ionic systems.
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