Utilization Of Triplet Excitons Research Articles

Harvesting Triplet Excitons in High Mobility Emissive Organic Semiconductor for Efficiency Enhancement of Light-Emitting Transistors.

Organic light-emitting transistors (OLETs), a kind of highly integrated and minimized optoelectronic device, demonstrate great potential applications in various fields. The construction of high-performance OLETs requires the integration of high charge carrier mobility, strong emission, and high triplet exciton utilization efficiency in the active layer. However, it remains a significant long-term challenge, especially for single component active layer OLETs. Herein, the successful harvesting of triplet excitons in a high mobility emissive molecule, 2,6-diphenylanthracene (DPA), through the triplet-triplet annihilation process is demonstrated. By incorporating a highly emissive guest into the DPA host system, an obvious increase in photoluminescence efficiency along with exciton utilization efficiency results in an obvious enhancement of external quantum efficiency of 7.2times for OLETs compared to the non-doped devices. Moreover, well-tunable multi-color electroluminescence, especially white emission with Commission Internationale del'Eclairage of (0.31, 0.35), from OLETs is also achieved by modulating the doping concentration with a controlled energy transfer process. This work opens a new avenue for integrating strong emission and efficient exciton utilization in high-mobility organic semiconductors for high-performance OLETs and advancing their related functional device applications.

High Electron Mobility Hot-Exciton Induced Delayed Fluorescent Organic Semiconductors.

The development of high mobility emissive organic semiconductors is of great significance for the fabrication of miniaturized optoelectronic devices, such as organic light emitting transistors. However, great challenge exists in designing key materials, especially those who integrates triplet exciton utilization ability. Herein, dinaphthylanthracene diimides (DNADIs), with 2,6-extended anthracene donor, and 3'- or 4'-substituted naphthalene monoimide acceptors were designed and synthesized. By introducing acceptor-donor-acceptor structure, both materials show high electron mobility. Moreover, by fine-tuning of substitution sites, good integration with high solid state photoluminescence quantum yield of 26%, high electron mobility of 0.02 cm2 V-1 s-1, and the feature of hot-exciton induced delayed fluorescence was obtained in 4'-DNADI. This work opens a new avenue for developing high electron mobility emissive organic semiconductors with efficient utilization of triplet excitons.

High Electron Mobility Hot‐Exciton Induced Delayed Fluorescent Organic Semiconductors

AbstractThe development of high mobility emissive organic semiconductors is of great significance for the fabrication of miniaturized optoelectronic devices, such as organic light emitting transistors. However, great challenge exists in designing key materials, especially those who integrates triplet exciton utilization ability. Herein, dinaphthylanthracene diimides (DNADIs), with 2,6‐extended anthracene donor, and 3′‐ or 4′‐substituted naphthalene monoimide acceptors were designed and synthesized. By introducing acceptor‐donor‐acceptor structure, both materials show high electron mobility. Moreover, by fine‐tuning of substitution sites, good integration with high solid state photoluminescence quantum yield of 26 %, high electron mobility of 0.02 cm2 V−1 s−1, and the feature of hot‐exciton induced delayed fluorescence were obtained in 4′‐DNADI. This work opens a new avenue for developing high electron mobility emissive organic semiconductors with efficient utilization of triplet excitons.

Ternary Exciplexes for Enhanced Two-Photon Excited Fluorescence by the Synergy Effect of Dual Reverse Intersystem Crossing Channels

A nonlinear optical (NLO) ternary exciplex is developed using a two-photon absorbing acceptor material tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB), a two-photon absorbing donor material 4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline] (TAPC), and a linear optical acceptor material 2,4,6-tris(1,1′-biphenyl)-1,3,5-triazine (T2T). In the ternary mixture, the high-energy exciplex TAPC:3TPYMB and the low-energy exciplex TAPC:T2T generate an effective synergy effect on the basis of their reverse intersystem crossing (RISC) channels to achieve further utilization of triplet excitons, giving rise to significantly enhanced one- and two-photon excited fluorescence properties. The highest photoluminescence quantum yield (PLQY) of the ternary exciplex 3TPYMB:TAPC:T2T measured in air atmosphere is ∼77.8%, which is greatly improved compared to that of the binary exciplex TAPC:T2T (∼39.6%) and the binary exciplex TAPC:3TPYMB (∼3.7%). More interestingly, the ternary exciplex also exhibits enhanced two-photon excited fluorescence under long-wavelength laser excitation. In comparison, no improvement in PLQY is observed in another ternary exciplex 3TPYMB:4,4′,4″-tris(carbazole-9-yl)triphenylamine (TCTA):T2T, which lacks an effective synergy effect between its high- and low-energy exciplex RISC channels. Our synergistic dual-channel RISC strategy may be helpful for the design of multicomponent thermally activated delayed fluorescence (TADF) NLO materials and facilitate the development of NLO applications.

A high-performance dual-functional organic upconversion device with detectivity approaching 1013 Jones and photon-to-photon efficiency over 20.

Organic upconversion devices (UCDs) are a cutting-edge technology and hot topic because of their advantages of low cost and convenience in the important applications of near-infrared (NIR) detection and imaging. However, to realize utilization of triplet excitons (T1), previous UCDs have the drawback of heavily relying on toxic and costly heavy-metal-doped emitters. More importantly, due to poor performance of the detecting unit and/or emitting unit, improving their detectivity (D*) and photon-to-photon conversion efficiency (ηp-p) is still a challenge for real applications. Here, we report a high-performance dual-functional purely organic UCD that has an outstanding D* approaching 1013 Jones and a high ηp-p of 20.1% in the NIR region, which are some of the highest values among those reported for UCDs. The high performance is credited to the excellent D* of the detecting unit, exceeding 1014 Jones, and is also attributed to efficient T1 utilization via a dual reverse intersystem crossing channel and high optical out coupling achieved via a high horizontal dipole ratio in the emitting unit. The high D* and ηp-p enable the UCD to detect 850 nm light at as little as 0.29 μW cm-2 and with a high display contrast of over 70 000 : 1, significantly improving the potential of practical applications of UCDs in NIR detection and imaging. Furthermore, a fast rise time and fall time of 8.9 and 14.8 μs are also achieved. Benefiting from the high performance, consequent applications of low-power pulse-state monitoring and fine-structure bio-imaging are successfully realized with high quality results by using our organic UCDs. These results demonstrate that our design not only eliminates dependence of UCDs on heavy-metal emitters, but also takes their performance and applications to a high level.

Halogenated Thermally Activated Delayed Fluorescence Materials for Efficient Scintillation.

Organic scintillators, materials with the ability to exhibit luminescence when exposed to X-rays, have aroused increasing interest in recent years. However, the enhancement of radioluminescence and improving X-ray absorption of organic scintillators lie in the inherent dilemma, due to the waste of triplet excitons and weak X-ray absorption during scintillation. Here, we employ halogenated thermally activated delayed fluorescence materials to improve the triplet exciton utilization and X-ray absorption simultaneously, generating efficient scintillation with a low detection limit, which is one order of magnitude lower than the dosage for X-ray medical diagnostics. Through experimental study and theoretical calculation, we reveal the positive role of X-ray absorption, quantum yields of prompt fluorescence, and intersystem crossing in promoting the radioluminescence intensity. This finding offers an opportunity to design diverse types of organic scintillators and expands the applications of thermally activated delayed fluorescence.

High-efficiency emissive dendritic phosphorescent iridium (III) complex with thermally activated delayed fluorescence molecules as functional light-harvesting moieties

Phosphorescent iridium (III) complexes are considered as competitive candidates for fabricating efficient and stable display and illumination devices by the virtue of excellent exciton utilization. Nevertheless, the high-efficiency phosphorescent emitters available for solution-processed fabrication, are still deemed unsatisfactory for the mainstream industries. In this context, a valid strategy of linking thermally activated delayed fluorescence (TADF) group covalently to phosphorescent iridium (III) complexes was proposed, in which TADF groups function as light-harvesting entities. In this way, the TADF units within the prepared complex TriTADF-Ir(dFppy)3, can effectively transfer energy to the phosphor core and thus boost device performances and reduce efficiency roll-off via alleviating the triplet exciton annihilations. As a result, the photoluminescence quantum yield of TriTADF-Ir(dFppy)3 blend films can reach to nearly 73 %. Thanks to the peripheral TADF dendrons, flexible TriTADF-Ir(dFppy)3 can be employed in fabricating solution-processed phosphorescent organic light-emitting diodes (PhOLEDs) with greenish-blue emission, which achieve external quantum efficiency value over 20 % and maintaining around 16 % at 1000 cd/m2. Overall, this result manifests that the effective utilization of triplet excitons and consequently enhanced device performance of solution-processed PhOLEDs can be accomplished by utilizing TADF molecules as peripheral light-harvesting moieties to construct dendritic phosphorescent emitters.

Improving excitons utilization of blue thermally activated delayed fluorescence emitter to achieve highly efficient solution-processed hybrid white organic light-emitting diodes

5-(5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-10,15-diphenyl-10,15-dihydro-5H-diindolo[3,2-a:3′,2′-c]carbazole (DBA-DI) with high triplet energy was utilized as efficient blue emission dopant to construct solution-processed thermally activated delayed fluorescence-phosphorescence (TADF-phosphorescence) hybrid white organic light-emitting diodes (WOLEDs). Meanwhile, a series of TADF-phosphorescence hybrid WOLEDs composed of bis(2-phenylquinoline) (2,2,6,6-tetramethylheptane-3,5-dionate)iridium(III) (PQ2Ir(dpm)), tris(2-(4-tolyl)-phenylpyridine)iridium (Ir(mppy)3) and DBA-DI are successfully developed by introducing the co-host system consist of poly(N-vinylcarbazole) (PVK) and 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPy) with high color rendering index (CRI) and improving the utilization of triplet excitons. Furthermore, energy transfer processes among different emitters were investigated in detail based on absorbance spectra, photoluminescence and transient photoluminescence spectra. Ultimately, the Commission Internationale de I'Eclairage coordinates of the optimum solution-processed WOLEDs in warm-white emission region are (0.41, 0.41) and high CRI is 82. Furthermore, the same device realized outstanding efficiencies of 32.14 cd A−1, 21.00 lm W−1 and 15.1% at high brightness of 1000 cd m−2.

Multiple‐Resonance‐Type TADF Emitter as Sensitizer Improving the Performance of Blue Fluorescent Organic Light‐Emitting Diodes

AbstractDue to the limitation of donor and acceptor group selection, the efficient thermally activated delayed fluorescence (TADF) type sensitizer used for blue organic light‐emitting diodes (OLEDs) is rare. Multiple resonance (MR) type TADF emitters can easily achieve efficient blue emission. And the compounds exhibit small Stokes shift and lower absorption energy under the same emission color compared with traditional TADF, mitigating the damage of high‐energy absorption of sensitizer on material stability. However, their characteristics as sensitizers have not been explored. In this work, a deep‐blue MR‐TADF compound (3tPAB) is selected as a sensitizer for both blue traditional fluorescence and MR‐TADF OLED. Given the improved photoluminescence quantum yield and the utilization of triplet excitons, the TADF‐sensitized fluorescent device using 3tPAB as sensitizer presents a maximum external quantum efficiency (EQEmax) of 14.4%, showing ≈2.4 times increase compared with the device without sensitizer. More impressively, TADF‐sensitized TADF (TST) device using 3tPAB as sensitizer and MR‐TADF compound PhDMAC‐BN as emitter exhibits EQEmax of 33.9%. And in TST device, efficient Förster energy transfer is demonstrated, thus, the device can maintain high color purity. The work first demonstrates the feasibility of MR‐TADF as a sensitizer and provides a new strategy for developing high‐performance blue OLED with high color purity.

Synergetic Horizontal Dipole Orientation Induction for Highly Efficient and Spectral Stable Thermally Activated Delayed Fluorescence White Organic Light‐Emitting Diodes

AbstractRadiative exciton generation and light out‐coupling are two crucial factors for highly efficient organic light‐emitting diodes (OLEDs). Herein, a thermally activated delayed fluorescence (TADF) material DspiroS‐TRZ with high horizontal dipole ratio (HDR, Θ// = 82%) is utilized as the blue emitter as well as the host for an orange‐red TADF emitter TPA‐AQ to fabricate white OLEDs. A synergetic horizontal dipole orientation induction on the transition dipole moment of TPA‐AQ is achieved by the highly orientated DspiroS‐TRZ, resulting in high HDR (Θ// = 96%) of the orange‐red emitter. Owing to the simultaneous efficient triplet exciton utilization and highly orientated binary system, a maximum external quantum efficiency (EQEmax) of 29.3% is achieved for single emission layer (EML) white OLED, with an excellent white light out‐coupling efficiency of 34%. In addition, the carrier recombination in the EML is further regulated by inserting an exciton regulation emission layer, which can relieve the trapping effect of the orange‐red emitter and guarantee stable Langevin recombination and energy transfer processes for improved electroluminescence spectral stability. An EQEmax of 31.2% is ultimately achieved for the double‐EML white OLED, highlighting the key role of horizontal dipole orientation induction and carrier recombination modulation for highly efficient and spectral stable white OLEDs.

Harvesting the Triplet Excitons of Quasi-Two-Dimensional Perovskite toward Highly Efficient White Light-Emitting Diodes

Utilization of triplet excitons, which generally emit poorly, is always fundamental to realize highly efficient organic light-emitting diodes (LEDs). While triplet harvest and energy transfer via electron exchange between triplet donor and acceptor are fully understood in doped organic phosphorescence and delayed fluorescence systems, the utilization and energy transfer of triplet excitons in quasi-two-dimensional (quasi-2D) perovskite are still ambiguous. Here, we use an orange-phosphorescence-emitting ultrathin organic layer to probe triplet behavior in the sky-blue-emitting quasi-2D perovskite. The delicate white LED architecture enables a carefully tailored Dexter-like energy-transfer mode that largely harvests the triplet excitons in quasi-2D perovskite. Our white organic-inorganic LEDs achieve maximum forward-viewing external quantum efficiency of 8.6% and luminance over 15 000 cd m-2, exhibiting a significant efficiency enhancement versus the corresponding sky-blue perovskite LED (4.6%). The efficient management of energy transfer between excitons in quasi-2D perovskite and Frenkel excitons in the organic layer opens the door to fully utilizing excitons for white organic-inorganic LEDs.

Multiple charge transfer disk-like emitters with fast fluorescence radiation rate and high horizontal dipole orientation for pure blue organic light-emitting diodes

• Multiple CT channels and 3 LE states contribute to the speedy k r and RISC processes. • High Θ and small FWHM are realized due to the rigid disk-like structure. • η r and η out above 30% are achieved owing to triplet exciton utilization and high Θ . • EQE above 10% was realized for the standard blue device based on BO3N. The efficiency of pure blue Organic light-emitting diodes (OLEDs) still needs to be improved, which is limited by the utilization of the forbidden transition triplet excitons and low light-out-coupling efficiency in devices. Herein, two blue emitters were developed through combining multiple diphenylamine (DPA) donors with an oxygen-bridged boron (DBA) or triphenyl triazine (TRZ) acceptor. Notably, a narrow-band deep blue emission with a peak of 423 nm and a Full-width at half-maximum (FWHM) of 34 nm is realized for the boron-based emitter in toluene solution. Thanks to their multiple Charge transfer (CT) channels and high orientated disk-like structure, high radiative transition rates ( k r > 10 8 s −1 ) and high horizontal emitting dipole ratios ( Θ > 80%) can be realized simultaneously. Meanwhile, the introduction of the peripheral DPA units can also provide multiple localized triplet ( 3 LE) states for spin up-conversion of forbidden transition triplet excitons. Owing to the effective up-conversion of triplet excitons and high light-out-coupling efficiency, maximum external quantum efficiency of more than 10% is achieved for the boron emitter-based pure blue OLEDs with a Commission Internationale de l’Eclairage (CIE) coordinates of (0.14, 0.08).

Using fullerene fragments as acceptors to construct thermally activated delayed fluorescence emitters for high-efficiency organic light-emitting diodes

Fragments of fullerene are used as acceptor segments for the first time to construct two thermally activated delayed fluorescence (TADF) compounds DBCP and FAP. Both compounds exhibit similar highly twisted geometries and separated frontier molecular orbital distributions. While on the other hand, their locally exited triplet energy levels from acceptor moieties (3LEA) are fine-tunable owning to the different structural stress in the fragments, resulting in different lowest triplet excited state (T1) features. In DBCP, the 3LEA is the high lying state and thus DBCP exhibits a small singlet–triplet energy difference of 0.10 eV and a high photoluminescence quantum yield (ΦPL) of 89% with excellent TADF characteristics; while T1 of FAP is 3LEA, and thus, FAP displays poor triplet exciton utilization with ΦPL of only 54%. In organic light-emitting diodes (OLEDs) based on DBCP and FAP as dopants, maximum external quantum efficiencies of 20.2% and 12.8% are respectively achieved. This work not only demonstrates for the first time that fullerene fragments can be used as key building blocks for TADF emitters, it also proves in principle that pure hydrocarbon mobilities without any electronegative heteroatom can also be employed as acceptor segment in high performance TADF emitters.

Critical Role of High‐Lying Triplet States for Efficient Excitons Utilization in High‐Performance Non‐Doped Deep‐Blue Fluorescent and Hybrid White Organic Light‐Emitting Diodes

AbstractFor organic light‐emitting diodes (OLEDs), the characteristics of high‐lying excited states of pure organic materials significantly affect the utilization of triplet excitons, which are critical in the process of electroluminescence. Herein, two novel molecules, PT‐1 and PT‐2, with deep‐blue emission are obtained, which exhibit nearly identical photophysical behavior in the photoluminescence process. However, the remarkable distinction in the characteristics of the high‐lying triplet excited states between PT‐1 and PT‐2 leads to a significant difference in the electroluminescence performance. Moreover, the non‐doped OLED based on PT‐1 exhibits maximum external quantum efficiency (ηext) of 6.63% with a low efficiency roll‐off. In addition, the authors employ PT‐1 as the phosphorescent host materials to fabricate two‐color hybrid white OLEDs (WOLEDs), from which they can realize the transformation from warm‐white to quasi‐white light by tuning the thickness of emission layer, with maximum ηext and power efficiency (ηp) of 23.93%/84.37 lm W−1 and 10.49%/33.96 lm W−1, respectively. These results deeply demonstrate the effects of high‐lying excited states on electroluminescence and facilitate the preparation of functional OLEDs.

Effect of hybridized local and charge transfer molecules rotation in excited state on exciton utilization

The fluorescent molecules utilizing hybridized local and charge-transfer (HLCT) state as potential organic light-emitting diodes materials attract extensive attention due to their high exciton utilization. In this work, we have performed the density functional theory method on three HLCT-state molecules to investigate their excited-state potential energy surface (PES). The calculated results indicate the T1 and T2 energy gap is quite large, and the T2 is very close to S1 in the energy level. The large gap is beneficial for inhibiting the internal conversion between T1 and T2, and quite closed S1 and T2 energies are favor for activating the T2 → S1 reverse intersystem crossing path. However, considering the singlet excited-state PES by twisting the triphenylamine (TPA) or diphenylamine (PA) group, it can be found that the TPA or PA group almost has no influence on T1 and T2 energy levels. However, the plots of S1 PES display two kinds of results that the S1 emissive state is dominated by charge-transfer (CT) or HLCT state. The CT emission state formation would decrease the S1 energy level, enlarge the S1 and T2 gap, and impair the triplet exciton utilization. Therefore, understanding the relationship between the S1 PES and molecular structures is important for designing high-performance luminescent materials utilizing HLCT state.

High-performance red and white organic light-emitting diodes based on a novel red thermally activated delayed fluorescence emitter in an exciplex matrix

Blue and green organic emitters based on thermally activated delayed fluorescence (TADF) mechanism have made great progress in organic light-emitting diode (OLED) applications, whereas red and white OLEDs with this kind of emitters are lagging behind. In this text, we develop high-performance red and white OLEDs by doping a novel red TADF emitter 10,10'-(11,12-diphenyldibenzo[a,c]phenazine-3,6-diyl)bis(10H-phenoxazine) (DBBPZ-DPXZ) into a blue emissive exciplex matrix. The highly rigid components and twisted donor-acceptor (D-A) structure of DBBPZ-DPXZ can suppress non-radiation decays and guarantee a small ΔEST, which results in effective exciton utilization. Meanwhile, the exciplex matrix can also provide additional reverse intersystem crossing (RISC) channel and enhance the utilization of triplet excitons. And thus, with doping 6 wt% DBBPZ-DPXZ into the exciplex host, red OLED with an electroluminescence peak at 628 nm and a high EQE of 20.8% is achieved. Moreover, by dropping doping concentration of DBBPZ-DPXZ into 0.2 wt%, a white OLED with Commission Internationale de l'Eclairage of (0.40, 0.38) at the luminance of 1000 cd m−2 and EQE of 20.7% is realized.

Light Amplification and Efficient Electroluminescence from a Solution‐Processable Diketopyrrolopyrrole Derivative via Triplet‐to‐Singlet Upconversion

AbstractOver the years, achieving efficient electroluminescence (EL) while simultaneously having low light amplification thresholds under optical excitation has been the key to progression toward the long‐thought objective of electrically pumped organic lasers. While significant progress in this regard has been made for organic semiconductors emitting in the blue–green region of the visible spectrum, organic laser dyes with low‐energy emission (>600 nm) still suffer from high amplified spontaneous emission (ASE) thresholds and low external quantum efficiencies (EQEs) in devices. Herein, low ASE thresholds and efficient EL are reported from a solution‐processable organic laser dye dithiophenyl diketopyrrolopyrrole (DT‐DPP). The ASE threshold of 4 µJ cm−2 at the wavelength of 620 nm is obtained while making constructive use of triplet excitons by doping DT‐DPP in a green‐emitting host matrix, which exhibits thermally activated delayed fluorescence (TADF). The organic light‐emitting diode fabricated from this system gives a high EQE of 7.9% due to the efficient utilization of triplet excitons. Transient EL studies further show that a high reverse intersystem crossing rate is crucial in achieving lasing under electrical pumping from such TADF‐assisted fluorescent systems.

Flexible all fluorescence white organic light emitting device with over 22% EQE by stepped reverse intersystem crossing channels based on ternary exciplex

Improvement of the utilization of triplet excitons for thermally activated delayed fluorescence (TADF) emitter-based white organic light emitting devices (WOLEDs) is a key scientific challenge. In this study, a new strategy with stepped reverse intersystem crossing (RISC) channels induced by new ternary exciplex was proposed to enhance up-conversion of non-radiative triplet excitons. A flexible TADF WOLED with external quantum efficiency (EQE) of 22.7% and a power efficiency of 62.5 lmW −1 was demonstrated. At 1000 cdm −2 , the EQE still remained at 21.4%, showing low efficiency roll-off of 5.7%. It is attributed to the reduced non-radiative triplet excitons stack, which suppressed the triplet–triplet quenching. Moreover, the new ternary exciplex-based WOLED system mCP: DMAC-DPS:PO-T2T:4CZPNPh exhibited rate constant of RISC process of 2.5 × 10 6 s −1 , and about 2 times photoluminescence quantum yield over binary exciplex. The high efficiency effectively demonstrated that the proposed multiple triplet excitons capture process is an effective strategy to improve the utilization of triplet excitons. Moreover, the novel strategy can be a promising approach for the further development of WOLED. ● New designed ternary exciplex was proposed and exhibit high efficiency,high photoluminescence quantum yield (PLQY). ● Novel strategy with stepped reverse intersystem crossing channels was introduced to improve the triplet excitons utilization and the PLQY of fluorescence based OLED. ● The flexible all fluorescence WOLED achieved maximum external quantum efficiency, power efficiency, current efficiency of 22.7%, 62.5 lm/W, 57.8 cd/A. At 1000 cd/m 2 , the external quantum efficiency is still remain 21.4%, exhibit superior efficiency stability.

Pure-Blue Fluorescence Molecule for Nondoped Electroluminescence with External Quantum Efficiency Approaching 13%

A pure-blue light-emitting material is one of the key components in the preparation of organic light-emitting diode (OLED) displays. Although high-efficiency blue OLEDs have been realized in therma...

Thermally Assisted Fluorescent Polymers: Polycyclic Aromatic Materials for High Color Purity and White-Light Emission.

Thermally activated delayed fluorescence (TADF) sensitization of fluorescence is a promising strategy to improve the color purity and operational lifetime of conventional TADF organic light-emitting diodes (OLEDs). Here, we propose a new design strategy for TADF-sensitized fluorescence based on acrylic polymers with a pendant energy-harvesting host, a TADF sensitizer, and fluorescent emitter monomers. Fluorescent emitters were rationally designed from a series of homologous polycyclic aromatic amines, resulting in efficient and color-pure polymeric fluorophores capable of harvesting both singlet and triplet excitons. Macromolecular analogues of blue, green, and yellow fourth-generation OLED emissive layers were prepared in a facile manner by Cu(0) reversible deactivation radical polymerization, with emission quantum yields up to 0.83 in air and narrow emission bands with full width at half-maximum as low as 57 nm. White-light emission can easily be achieved by enforcing incomplete energy transfer between a deep blue TADF sensitizer and yellow fluorophore to yield a single white-emissive polymer with CIE coordinates (0.33, 0.39) and quantum yield 0.77. Energy transfer to the fluorescent emitters occurs at rates of 1-4 × 108 s-1, significantly faster than deactivation caused by internal conversion or intersystem crossing. Rapid energy transfer facilitates high triplet exciton utilization and efficient sensitized emission, even when TADF emitters with a low quantum yield are used as photosensitizers. Our results indicate that a broad library of untapped polymers exhibiting efficient TADF-sensitized fluorescence should be readily accessible from known TADF materials, including many monomers previously thought unsuitable for use in OLEDs.