Rong-Huei Yi

Tetrabenzodinaphthopyranthrene (TBDNP) with a combination of zigzag and fjord edges has been synthesized. TBDNP exhibits NIR emission in the range of 800–1000 nm with a photoluminescence quantum yield of 14%, and excellent self-blinking properties compared to reported near-infrared dyes. Moreover, TBDNP displays notable chiroptical properties with strong chiroptical activities from 300 to 850 nm and high g _abs up to 0.032 at 574 nm.

Abstract

Near-infrared (NIR) fluorophores are highly desirable for super-resolution fluorescence microscopy; however, their optical properties are typically relatively poor, with low photo-intensity (mean photon number below 1000), and unfavorably high on-off blinking duty cycle. In this work, the synthesis and characterization of tetrabenzodinaphthopyranthren (TBDNP) derivative as a novel nanographene that exhibits NIR emission in the range of 800–1000 nm with a photoluminescence quantum yield of 14% are reported. TBDNP demonstrated excellent self-blinking properties, in particular, mean photon number of >3000 and a low on–off-duty cycle (≈10⁻⁴), which are superior to reported NIR dyes, and can be successfully employed for the NIR super-resolution imaging. Moreover, TBDNP serves also as a chiral fluorophore, showing notable chiroptical activities from 300 to 850 nm with a high dissymmetry factor (g _abs) of 0.032 at 574 nm.

This work provided a facile strategy for achieving water-soluble polymeric afterglow materials with ultralong lifetime, wide color-tunability and persistent near-infrared luminescence via constructing three/four-component energy transfer systems that are capable of occurring non-traditional phosphorescence resonance energy transfer and two-step energy transfer cascade.

Abstract

Polymer-based room-temperature phosphorescence (RTP) materials show promising applications in anti-counterfeiting. To further realize multiscale and/or multimodal anti-counterfeiting, it is highly desirable to develop polymeric afterglow materials with multiple security features. Herein, a facile strategy is presented to endow polymeric afterglow materials with ultralong lifetime, wide color-tunability, persistent near-infrared (NIR) luminescence, and good water solubility via constructing non-traditional phosphorescence resonance energy transfer (PRET) and two-step sequential resonance energy transfer systems. Specifically, the 1-bromocarbazole derivatives with ultralong blue-color RTP property act as the energy donor while traditional dyes with red/NIR luminescence act as the energy acceptor. By simply regulating the doping composition and concentration of these non-traditional energy transfer systems, persistent and multicolor organic afterglow covering from the visible to NIR region is successfully realized. Notably, compared to the single-step PRET, the two-step sequential resonance energy transfer has the unique advantages of higher transfer efficiency of triplet excitons from the initial donor, a wider range of color-tunability mediated by the intermediary acceptor, and enhanced delayed fluorescence efficiency of the final acceptor. Finally, these water-soluble polymeric afterglow materials with ultralong lifetime, wide color-tunability, and persistent NIR luminescence show great potential applications in advanced anti-counterfeiting and information security technologies.

A molecular design concept to enhance reactive oxygen species (ROS) generation is presented, and full-wavelength visible light materials are synthesized and applied to photodynamic therapy and catalysis of endoperoxide formation. This work provides insight into improving the ROS efficiency of photosensitizers and controlling the release of ¹O₂ to achieve afterglow therapy.

Abstract

Organic photosensitizers (PSs) with aggregation-induced emission (AIE) characteristics have shown several advantages in photodynamic therapy (PDT). However, how to design PSs with the required optical and biological properties is a formidable challenge. In this work, a series of AIE active pyridine- and pyridinium-functionalized carbazole with different substituents are designed and synthesized. Compared to other analogs, BK-Pys-BP containing benzophenone moiety on the pyridinium unit produces reactive oxygen species (ROS) efficiently in the presence of light due to its large spin-orbit coupling constant to promote efficient intersystem crossing. Based on its structure, three molecules with enhanced donor–acceptor strength and conjugation are further investigated to realize emission covering the whole visible region. The cationic nature and excellent ROS generation ability of benzophenone-containing AIE photosensitizers allows for specific imaging of mitochondria, killing cancer cells, and as a singlet oxygen donor to catalyze the formation of endoperoxides. Thus, the present work presents an effective strategy for creating AIE photosensitizers with efficient ROS generation for wide biological applications.

Through the anion substitute strategy, the photophysical process, molecular accumulation, and characterization of self-assembled nanoparticles can be modified. Correspondingly, the various properties of aggregates are regulated, including the regulation of fluorescence and reactive oxygen production, the mechanochromism response properties, and the difference in the binding ability between molecules and organisms finally selectively illuminating S. aureus and C. albicans.

Abstract

Charged aggregation-induced emission luminogens (AIEgens) are highly valued materials with attractive applications. However, the discussion of charged AIEgens with the characteristics of charged compounds is always centered around the cationic luminescence part, and the possible influence brought by anion effects is usually ignored especially in the field of aggregate science. Coupled with the complicated synthesis and purification processes of the brand-new cationic nucleus, it is paramount to develop simpler and more feasible methods to enhance cognition and extend their performance. Herein, three new ionic compounds based on TPE-IQ-2TPA (TI2T) cationic core utilizing an anion substitution strategy are investigated. Interestingly, this strategy can modify molecular aggregation behavior regarding the photophysical process and arrangement of the molecules. Consequently, fluorescence emission, reactive oxygen species (ROS) generation ability, and mechanochromism response properties varied accordingly. Moreover, this strategic regulation of the physical parameters of self-assembled nanoparticles facilitates the visual identification of living or dead cells, while also selectively illuminating S. aureus and C. albicans. This study demonstrates that anion engineering is a powerful tool for investigating aggregated states and provides a new platform for practical applications of advanced materials, especially in the fields of stimulus-response, biological imaging, medical diagnosis, and treatment.

Molecular factors that control photoluminescence efficiencies of two-coordinate Au(I) complexes involve the emission energy and the charge in the Au 5d-orbital.

Abstract

This research elucidates the effects of structural modulations on electroluminescent Au(I) complexes, shedding light on factors governing radiative and nonradiative processes. A series of Au(I) complexes, fortified with ortho-substituents in carbene and amido ligands, are subjected to rigorous structural, photophysical, and quantum chemical investigations, which unveil distinct structural and electronic effects exerted by the ligands. The investigations reveal that nonradiative processes are governed primarily by the energy-gap law. Radiative processes are observed to have a weak correlation with the mutual interactions of the molecular orbitals of carbene and amido ligands. Rather, it is discovered that an accumulation of the negative charge in the Au 5d orbital in the excited state decelerates radiative processes. The effectiveness of these findings is substantiated through the larger external quantum efficiency of electroluminescence devices employing the Au(I) complex, in comparison to those based on the archetypical Au(I) complex and the organic thermally activated delayed fluorescent molecule. These compelling revelations underscore the untapped potential of Au(I) complexes in the advancement of electroluminescence technology and advocate for continued investigations into the intriguing domain of ligand structural control.

A donor of spiro[acridine-indoloacridine] enables a superior D–A type thermally activated delayed fluorescence emitter of AIA-TRZ with near-unity photoluminescence quantum yield and horizontal emitting dipole orientation, as well as fast but balanced k _r, k _ISC, and k _RISC rates. The AIA-TRZ-based organic light-emitting diodes achieve excellent performance with a high maximum external quantum efficiency of 37.3% and low efficiency roll-off of 11.2% at 1000 cd^·m⁻².

Abstract

Designing thermally activated delayed fluorescence (TADF) emitters with excellent photoluminescence quantum yield (PLQY), preferential horizontal emitting dipole orientation (𝛩_//), and fascinating ability to rapidly utilize both singlet and triplet excitons for radiation is crucial for high-performance organic light-emitting diodes (OLEDs) with both high efficiency and relieved efficiency roll-off. Integrating these advantages into a single TADF emitter is a formidable challenge. In this work, a spiro[acridine-indoloacridine]-based rigid donor, named AIA, is designed to establish a cooperatively long-axis extended and conjugation expanded donor–acceptor type TADF emitter (AIA-TRZ). The proof-of-the-concept emitter simultaneously achieves an excellent PLQY of 99%, a near-unity 𝛩_// of 99%, and balanced excited state dynamic parameters. OLEDs based on AIA-TRZ realize remarkable performance with an emission peak at around 480 nm, including doping concentration insensitivity, a maximum external quantum efficiency (EQE_max) of 37.3%, extremely low efficiency roll-off, and over 20% EQE even at 14000 cd m⁻².

A new concept to achieve bright afterglow materials via the manipulation of higher triplet excited states (T _n state, n ≥ 2) is reported. Unlike the conventional strategy based on heavy atom effect and n-π* transition, the concept of manipulating T _n states can selectively enhance intersystem crossing with phosphorescence lifetimes remaining long.

Abstract

Afterglow brightness represents one of the most important characteristics in the application of afterglow materials. High molar absorption coefficient, high afterglow efficiency, and long afterglow lifetimes are required to achieve intense afterglow. However, current strategies cannot simultaneously fulfill these requirements due to specific intrinsic problems. Here, based on the understanding of difluoroboron β-diketonate systems, the manipulation of higher triplet excited states is conceived to selectively enhance intersystem crossing with phosphorescence lifetimes remaining long. Aromatic substrates, which possess specific HOMO levels and T₁ levels, are selected for relay synthesis to form difluoroboron β-diketonate compounds with very close-lying S₁ and T₂ levels; according to the energy gap law, such systems exhibit strong intersystem crossing. Upon doping into rigid matrices, the resultant difluoroboron β-diketonate systems display the brightest ambient afterglow that has ever been observed.

Here, the sensitive organic scintillators are achieved via cocrystal design that promotes absorption and triplet exciton formation. The incorporation of heavy atoms facilitates X-ray absorption and promotes intersystem crossing. Meanwhile, the tailored coupling of acceptor and donor improves spin-orbit coupling and suppresses non-radiative recombination of triplet excitons. Thus, a stable and sensitive organic X-ray scintillator with imaging capability is realized.

Abstract

Organic materials show good mechanical flexibility, easy processing, and large-area manufacturing, while weak X-ray absorption and low sensitivity for X-ray scintillator media. As seen originally, this is a synergistic result of the lack of heavy elements in the molecule that can effectively truncate X-rays and the massive dissipation of triplet excitons produced by molecular ionization. Herein, cocrystal with phosphorescence enhancement is found to be brilliant in addressing the shortcomings of organic scintillators. The results show that heavy atoms can be easily introduce into the donor unit of organic cocrystal to satisfy the X-ray absorption and effectively activate the triplet excitons via promoting intersystem crossing (ISC). Moreover, the rational structural design of the acceptor molecule can achieve coupling with the donor for inhibiting the non-radiative loss of the triplet exciton. Finally, the preferred PNPA (4,4′-Dibromobiphenyl and N-phenylnaphthalen-2-amine) cocrystals achieve record X-ray-induce exciton utilization and emit bright phosphorescent light. Meanwhile, the related device shows durable radiation stability, spatial resolution (>11 lp mm⁻¹), low detection limit (<0.6 µGy_air s⁻¹), and effective dynamic imaging application. Hence, it is believed the organic cocrystal-designed principle can provide guidance to develop advanced sensitive X-ray scintillators in the future.

Various pyrene-based [2,2]PCP derivatives can be constructed by different substitution modes and connection patterns of [2,2]PCP cores and pyrene units. Diverse structures of these compounds lead to distinctive optical properties.

Abstract

We reported the synthesis of a series of structurally diverse CPL-active molecules, in which pyrene units were installed to chiral pm /po -[2,2]PCP scaffolds either with or without a triple bond spacer for pm/po -PCP-P1 and pm /po-PCP-P2, respectively. The X-ray crystallographic analyses revealed that these pyrene-based [2,2]PCP derivatives exhibited diverse structures and crystal packings in the solid phases. The pyrene-based [2,2]PCP derivatives exhibit various (chir)optical properties in organic solutions, depending on their respective structures. In a mixture of dioxane and water, pm /po-PCP-P1 emit green excimer fluorescence, whereas pm /po-PCP-P2 emit blue one. The chiroptical investigation demonstrated that R p-pm-PCP-P1 and R p-pm-PCP-P2 exhibited completely opposite CD and CPL signals even they possess the same chiral Rp-[2,2]PCP core. The same argument also holds for other chiral pyrene-based [2,2]PCP derivatives. The theoretical calculation revealed that these unusual phenomena were attributed to different orientation between transition electric dipole moments and the magnetic dipole moments originating from the presence or absence of a triple bond spacer. These pyrene-based [2,2]PCP derivatives display various colours and fluorescence emissions in the solid state and PMMA films, possibly due to the different packings as observed in the crystal structure. Moreover, these compounds also can interact with perylene diimide through π-π interactions, leading to near-white fluorescence.

Publication date: 1 December 2023

Source: Chemical Engineering Journal, Volume 477

Author(s): Shantaram Kothavale, Kiun Cheong, Seung Chan Kim, Songkun Zeng, Yafei Wang, Jun Yeob Lee

Publication date: 15 December 2023

Source: Chemical Engineering Journal, Volume 478

Author(s): Yu Feng, Xuming Zhuang, Yincai Xu, Jianan Xue, Cheng Qu, Qingyang Wang, Yu Liu, Yue Wang

Publication date: 15 December 2023

Source: Chemical Engineering Journal, Volume 478

Author(s): Taehyun Kim, Sunyoung Sohn, Sungjin Park, Wanuk Choi, Hyungju Ahn, Sungjune Jung, Taiho Park

Novel quinone compounds derived from doubly and triply linked diporphyrins and their metal complexes have been synthesized and characterized. Doubly linked diporphyrinquinone exhibits broad panchromatic absorption properties with significant red-shifts to 1300 nm upon metalation. In contrast, the metal complexes of the triply linked diporphyrinquinones exhibit sharp and strong absorption bands in the visible to near-infrared region owing to their higher symmetry. More information can be found in the Research Article by K.-i. Yamashita, D. Hirano, and K.-i. Sugiura (DOI: 10.1002/chem.202302637).

A series of bridged anthracenes was synthesized and their photostabilities were accessed. While the length of the bridges only plays a minor role, introduction of electron withdrawing ester-based linkers retards photooxidation most. Those esters bridged anthracenes could be prepared in reasonable yields and “proof-of-principle” organic light emitting diodes with deep blue emission were built, demonstrating their potential as emitters.

Abstract

The photooxidative stability of a series of doubly bridged anthracenes was evaluated after their preparation via twofold macrocyclization of a bis(resorcinyl)anthracene. Lightfastness correlates with the energy levels of the highest occupied molecular orbital (HOMO), resulting in superior stability of the tetraesters compared to the tetraethers. The lengths and steric demand of the linker only plays a minor role for the ester-based compounds, which can be prepared in reasonable yields and thus tested in proof-of-concept organic light-emitting diodes. Double ester-bridging allows deep blue electro-luminescence, highlighting the importance of the choice of the functional groups used for macrocyclization.

Incorporating less bulky cyano group to replace methyl on π bridge of donor-π-acceptor molecule instead strengthened the thermally activated delayed fluorescence feature through enhancing intramolecular charge transfer, and boosted photoluminescence quantum yield from 40 % to 94 % by increasing HOMO-LUMO overlap, finally led to an EQE of 14 % in blue OLED.

Abstract

In general, a large donor-acceptor dihedral angle is required to guarantee sufficient frontier molecular orbitals separation for thermally activated delayed fluorescence (TADF) emitters, which is intrinsically unfavorable for the radiative transition. We present a molecular design method favoring both reverse intersystem crossing (RISC) and radiative transitions even at a moderate D−A angle. A blue TADF emitter TrzBuCz-CN was designed with triazine/tert-butylcarbazole as donor/acceptor and cyano (CN) incorporated on the phenylene bridge. In comparison with the methyl decoration in similar way (TrzBuCz−Me), CN decoration reduced the D−A dihedral angle from 70° to 60°, which is intrinsically not favorable for sufficient FMO separation, but unexpectedly reduced the singlet and triplet energy gap (ΔE _ST) and thus facilitated TADF feature by pulling down the lowest singlet state energy. While the reduced distorsion instead improved the HOMO-LUMO overlap and boosted the fluorescence quantum yield from 41 % to 94 %. The blue organic light-emitting diode of TrzBuCz-CN exhibited an external quantum efficiency of 13.7 % with emission peak at 466 nm, greatly superior to 6.0 % of TrzBuCz−Me. The result provides a feasible design strategy to facilitate both RISC and radiation processes by CN decoration of the linking bridge of TADF emitters.

Here the wide-bandgap emitter fusing two ultraviolet multiple resonance fragments via a unique double-halide cyclized coupling reaction is presented. The resulting molecule can simultaneously achieve efficient violet-blue emission and narrowed spectra. The fabricated violet-blue electroluminescent device exhibits ideal performances with a high maximum external quantum efficiency of 20.5%.

Abstract

The spectral narrowing engineering of pure-organic emitters attracts great research interests in realizing high color purity. Here, the adjusted medium-range charge transfer (MCT) strategy of TIC-BO with rigid planar structure by fusing two typical UV-emitting multiple resonance (MR) fragments via the ingenious double-halide cyclized coupling reaction is reported. The resulting TIC-BO with MCT nature shows efficient violet-blue emission in dilute toluene and evaporated host–guest films, and desirably narrowed spectra are achieved by the suppression of structural relaxation and the shortened charge transfer states. The single-doped device with TIC-BO as emitter shows narrowed violet-blue electroluminescence peaked at 428 nm with full-width at half-maximum of 43 nm (0.28 eV), and the Commission Internationale de l’Éclairage coordinates of (0.160, 0.050). A maximum external quantum efficiency (EQE_max) of 20.50% is achieved, which is among the best results of the corresponding violet-blue emitting region. Further introduction of a stronger electron-donating carbazole group makes TIC-BNO exhibit red-shifted sky-blue emission with MR-dominant properties, and good device performance is received with EQE_max of 34.58%. The outstanding performances of TIC-BO successfully demonstrate the significance and prospect of the proposed molecular design strategy.

Nitro-benzyloxy BODIPY derivatives show unique dual-color photoconvertible ability, leading to a pronounced blue shift in the absorption and emission spectra under visible light irradiation. This process not only achieves efficient photoconversion, but also provides bright fluorescence for both the pre- and post-activation stages, enabling effective dual-color imaging of cells without phototoxicity using a 488 nm laser.

Abstract

Photoactivatable fluorophores are useful tools in live cell imaging due to precise spatial and temporal control. Herein, a tandem visible-light photodecaging and tautomerization strategy is proposed as an activation mechanism for the construction of photoconvertible boron dipyrromethenes (BODIPY) dyes, from which nitro-benzyloxy BODIPY derivatives are developed as a new class of visible light photoactivated fluorophores. Upon exposure to visible light, the nitro-benzyloxy moiety is released and the BODIPY moiety is converted to the keto-form BODIPY analog by tautomerization. The photoconversion process not only achieves over 50 nm blue shift of absorption/emission maxima but also provides bright fluorescence for both the pre- and post-activation forms. Mechanism studies indicate that no indications of radical species and singlet oxygen are involved in this unique photoconversion and both UV and visible light irradiation can efficiently activate this photoinduced release of the nitrobenzyl alcohol through photoexciting of BODIPY core rather than classical nitro-benzyloxy photocage. Cell and vesicle imaging is successfully performed using the new photoconversion dyes. The results show that these new photoconvertible dyes are highly efficient, universal, and non-cytotoxic, which are valuable for the development of promising photoactivated molecules.

The non-conjugated n–π spatial electron coupling strategy is implemented to modulate the triplet state of boron-dipyrromethene (BODIPY) for creating efficient near-infrared light-activable triplet fusion upconversion in solution and air-stable solid-state material.

Abstract

Effective strategies to manage the triplet state of chromophores are desirable in terms of their crucial role in photonic and optoelectronic technologies. However, triplet excited-state energy level regulation of organic molecules remains elusive. Here, non-conjugated n–π spatial electron coupling is demonstrated within boron-dipyrromethene (BODIPY) and can greatly reduce the low-lying triplet state (T₁) to 1.34 eV without the conventional need for π-conjugation extension. Moreover, the close alignment between T₁ states of this BODIPY derivative and the photosensitizer PtTNP contributes to the reversible triplet energy transfer, namely the intermolecular triplet excited-state equilibrium. Furthermore, to the best of the knowledge, the first BODIPY-based near-infrared light-activated triplet fusion upconversion (NIR TF-UC) with an upconversion quantum efficiency of 13.3% is implemented. On this basis, the air-stable solid-state NIR TF-UC material is successfully fabricated, whose upconverted emission can still be seen at an ultralow NIR power density of 6.4 mW cm⁻². This new strategy to implement triplet state modulation will accelerate the development of NIR TF-UC and other important areas involving triplet state, such as photoredox catalysis, photodynamic therapy, and photovoltaic devices.

Efficient intramolecular triplet–triplet annihilation up-conversion (Intra-TTU) in OLEDs using dimer-type molecular structure is reported. Compared to the molecular conformations in each molecule, the closely adjacent dimerized units within the effective radius of the electron exchange interaction will be considered as the reasonable factor to induce the Intra-TTU.

Abstract

It is well known that triplet–triplet annihilation upconversion (TTU) can enhance electroluminescence (EL) efficiency by converting two low-energy triplet excitons into one high-energy singlet exciton. However, conventional intermolecular TTU requires high doping concentration to activate, limiting device architecture. Here, six dimer molecules comprised of two anthracene units connected by a spacer unit are investigated, which have a possibility of the intramolecular TTU process. As a result, two dimer molecules show high TTU efficiencies close to the theoretical maximum even in dispersed, diluted conditions. By comparing these molecular conformations, a correlation is found between the dimer structures of two anthracene units and the TTU activity in the diluted condition, i.e., the 3D molecular structure with the exciton utilizing efficiency.

A “ternary asymmetries” strategy for developing ambipolar host materials is demonstrated by an asymmetric spiro skeleton substituted with carbazole donors and a phosphine oxide acceptor. The resulted host STXSPOtBCz2 effectively facilitates singlet radiation and suppresses triplet quenching of yellow thermally activated delayed fluorescence dopants, resulting in the state-of-the-art photoluminescence and electroluminescence quantum efficiencies beyond 90% and 30%, respectively.

Abstract

Yellow thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) are indispensable for lighting, navigation, caution, and so on; however, their development is far behind those of three-elementary-color and white analogs, partially because of the lack of host specificity. In this contribution, spiro[bithoxanthene] (ST) and spiro[thioxanthene-xanthene] (STX) are used as spiro skeletons to form asymmetric ternary structures through introducing two electron-donating tert-butyl carbazole (tBCz) and one electron-withdrawing diphenyl phosphine oxide (DPPO) groups on different rings. The resulting hosts named STSPOtBCz2 and STXSPOtBCz2 not only inherit the steric hindrance of their spiro skeletons, but also achieve the ambipolar characteristics. Their suitable triplet energy levels (T₁) of ≈2.5 eV support efficient energy transfer to a conventional yellow TADF emitter 4CzTPNBu with the T₁ of ≈2.2 eV. It is shown that compared to STSPOtBCz2 with a symmetric core, the accumulated asymmetry of the spiro skeleton and the kind, number, and position of substitution groups in STXSPOtBCz2 further suppresses the emission quenching, resulting in the state-of-the-art photoluminescent and electroluminescent quantum efficiencies of 93% and 30.6%, respectively. The maximum power efficiency beyond 90 lm W⁻¹ further demonstrates the great potential of multi-asymmetric host systems for energy-saving practical application.

Heterofission is an essential process in pure organic room temperature phosphorescence materials, leading to the ultrafast formation of triplet exciton. Suitable host and guest candidates are designed according to their molecular orbital nature.

Abstract

Room temperature phosphorescence (RTP) from pure organic materials, whether in crystalline or film phases, has recently attracted considerable attention. Experimental evidence increasingly suggests that RTP originates from isomeric dopants (impurity) rather than pure compounds. The underlying mechanism and molecular design principles have remained elusive. Herein, the “heterofission mechanism” for RTP is proposed, wherein a singlet excited state is split into two triplets, one remains within the host, while the other migrates to the guest (dopant) molecule, satisfying E _host(S₁) ≈ E _host(T₁) + E _guest(T₁). It is found that all the dopants possess a low triplet excited state, meeting the energy requirement for the heterofission process. The sum of the calculated emission spectra from these two triplets overlaps well with the experimentally measured broad phosphorescent spectra. Furthermore, the calculated heterofission rates are expected to occur at the picosecond timescale. Efficient Dexter energy transfer leads to the guest predominantly dominating the RTP. Based on this mechanism, we can predict potential host and guest candidates to expand the family of pure organic RTP materials.

Based on experimental data, machine learning models are established using quantum chemistry calculated descriptors or topological/physical/chemical molecular descriptors as variables, thereby quantitatively identifying the key factors influencing the horizontal transition dipole orientation of luminescent materials and favorable molecular design. The models are double-validated by accurately predicting the horizontal orientation ratio of the transition dipole moment of new host-guest systems.

Abstract

Realizing the horizontal orientation of molecular transition dipole moment (TDM) can greatly improve the out-coupling efficiency and the resultant external quantum efficiency (EQE) of organic light-emitting diodes (OLEDs). Herein, key parameters governing the horizontal TDM have been continuously explored. However, quantitatively identifying the key parameters from the molecular structure viewpoint is rather challenging due to the complexity of the influencing parameters. Here, by training the machine learning (ML) models using the experimental results, the quantitative relationship between the molecular structure and the horizontal TDM ratio (ϴ) of thermally activated delayed fluorescent (TADF) emitters in the host-guest films is identified. The molecular structure is represented by either quantum chemistry-calculated structural descriptors or topological/physical/chemical molecular descriptors. Key descriptors are ranked and can be used for guiding molecular structure design. Moreover, the accuracy of ML models is double-verified by comparing the predicted results with experimental ϴ values and the trend of experimental EQE based on a group of materials. Using compressed sensing technology, the low-dimension material space is also visually constructed based on key descriptors, and the results are consistent with those of the ML models.

By integrating multi-resonance thermally activated delayed fluorescence (TADF) moiety into the conjugated backbone, blue TADF conjugated polymers with narrowband emission are successfully developed. Solution-processed devices based on PCzDBN3 exhibit state-of-the-art performance with maximum external quantum efficiencies (EQEs) of up to 17.9 %, peak at 479 nm and full-width at half-maximum (FWHM) of 28 nm.

Abstract

The development of thermally activated delayed fluorescence (TADF) polymers with narrowband emission, particularly in the blue region, remains a formidable challenge. Herein, a new approach is demonstrated for blue TADF conjugated polymers by integrating multiresonance TADF moiety into the conjugated backbone. All the new polymers exhibit TADF characteristics with narrowband blue emission with full-width at half-maximums (FWHMs) of 23 nm. The solution-processed OLEDs based on these polymers achieve a maximum external quantum efficiency (EQE_max) of 17.9% with the emission peak at 479 nm and FWHM of 28 nm. The main-chain type MR-TADF polymer shed light on the development of narrowband emissive TADF conjugated polymers.

Achieving chromophores with integrated aggregation-induced emission (AIE) and twisted intramolecular charge transfer (TICT) properties is attractive but has yet to be exemplified mechanistically. Here, molecular engineering strategy is finded for endowing chromophores the superior TICT and AIE properties due to the electron-donor moiety with strong electron-donating properties and hydrophobic effect.

Abstract

The pursuit of sensitive fluorescent chromophores with integrated aggregation-induced emission (AIE) and twisted intramolecular charge transfer (TICT) properties are attractive due to the tunable emission properties and increased intensity. However, this type of chromophore has yet to be exemplified mechanistically. In this study, a strategy is presented for manipulating the formation of TICT and the AIE effect through molecular engineering. The feasibility of TICT properties is validated by theoretical calculations and ultrafast spectroscopies. By precisely adjusting the hydrophobicity of the donor group, the fluorescence is significantly enhanced through the addition of poor solvent. These findings not only provide mechanistic elucidation for chromophores exhibiting integrated TICT and AIE properties in various environmental conditions but also underscore the critical factors for the systematic design of chromophores with high tunability and strong emissions.