Rong-Huei Yi

An efficient strategy is proposed for achieving narrow-band, long-lived, and full-color organic long-persistent luminescence (LPL) by isolating multi-resonant thermally activated delayed fluorescent fluorophores in a steroid-type host capable of exciton dissociation and recombination. Through efficient FRET, the LPL exhibits a small full-width at a half-maximum of 33 nm, persistent time exceeding 10 s, and tunable color among 414–600 nm.

Abstract

Organic afterglow with long-persistent luminescence (LPL) after photoexcitation is highly attractive, but the realization of narrowband afterglow with small full-width at half-maximum (FWHM) is a huge challenge since it is intrinsically contradictory to the triplet- and solid-state emission nature of organic afterglow. Here, narrow-band, long-lived, and full-color organic LPL is realized by isolating multi-resonant thermally activated delayed fluorescent (MR-TADF) fluorophores in a glassy steroid-type host through a facile melt-cooling treatment. Such prepared host becomes capable of exciton dissociation and recombination (EDR) upon photoirradiation for both long-lived fluorescence and phosphorescence; and, the efficient Förster resonance energy transfer (FRET) from the host to various MR-TADF emitters leads to high-performance LPL, exhibiting small FWHM of 33 nm, long persistent time over 10 s, and facile color-tuning in a wide range from deep-blue to orange (414–600 nm). Moreover, with the extraordinary narrowband LPL and easy processability of the material, centimeter-scale flexible optical waveguide fibers and integrated FWHM/color/lifetime-resolved multilevel encryption/decryption devices have been designed and fabricated. This novel EDR and singlet/triplet-to-singlet FRET strategy to achieve excellent LPL performances illustrates a promising way for constructing flexible organic afterglow with easy preparation methods, shedding valuable scientific insights into the design of narrow-band emission in organic afterglow.

A series of benzo[a]phenazine (BP)-based acceptors achieved through an isomerization chlorination strategy is presented, namely NA1, NA2, NA3, and NA4. The ortho-xylene (o-XY) processed binary organic solar cells (OSCs) based on PM6:NA3 yields an efficiency of 18.94%. Importantly, the o-XY processed ternary OSC device based on PM6:D18-Cl:NA3 exhibits an efficiency as high as 19.75%.

Abstract

High-performance organic solar cells often rely on halogen-containing solvents, which restrict the photovoltaic industry. Therefore, it is imperative to develop efficient organic photovoltaic materials compatible with halogen-free solvents. Herein, a series of benzo[a]phenazine (BP)-core-based small-molecule acceptors (SMAs) achieved through an isomerization chlorination strategy is presented, comprising unchlorinated NA1, 10-chlorine substituted NA2, 8-chlorine substituted NA3, and 7-chlorine substituted NA4. Theoretical simulations highlight NA3's superior orbit overlap length and tight molecular packing, attributed to interactions between the end group and BP unit. Furthermore, NA3 demonstrates dense 3D network structures and a record electronic coupling of 104.5 meV. These characteristics empower the ortho-xylene (o-XY) processed PM6:NA3 device with superior power conversion efficiency (PCE) of 18.94%, surpassing PM6:NA1 (15.34%), PM6:NA2 (7.18%), and PM6:NA4 (16.02%). Notably, the significantly lower PCE in the PM6:NA2 device is attributed to excessive self-aggregation characteristics of NA2 in o-XY. Importantly, the incorporation of D18-Cl into the PM6:NA3 binary blend enhances crystallographic ordering and increases the exciton diffusion length of the donor phase, resulting in a ternary device efficiency of 19.75% (certified as 19.39%). These findings underscore the significance of incorporating new electron-deficient units in the design of efficient SMAs tailored for environmentally benign solvent processing of OSCs.

Novel efficient thermally activated delayed fluorescence molecules with regular folded sandwich configurations are constructed using 11,12-dihydroindolo[2,3-a]carbazole as bridge, xanthone as acceptor, and dibenzothiophene, dibenzofuran, 9-phenylcarbazole and indolo[3,2,1-JK]carbazole as donors. They can function efficiently as emitters in organic light-emitting diodes, providing high electroluminescence efficiencies of up to 30.6 %.

Abstract

Constructing folded molecular structures is emerging as a promising strategy to develop efficient thermally activated delayed fluorescence (TADF) materials. Most folded TADF materials have V-shaped configurations formed by donors and acceptors linked on carbazole or fluorene bridges. In this work, a facile molecular design strategy is proposed for exploring sandwich-structured molecules, and a series of novel and robust TADF materials with regular U-shaped sandwich conformations are constructed by using 11,12-dihydroindolo[2,3-a]carbazole as bridge, xanthone as acceptor, and dibenzothiophene, dibenzofuran, 9-phenylcarbazole and indolo[3,2,1-JK]carbazole as donors. They hold outstanding thermal stability with ultrahigh decomposition temperatures (556–563 °C), and exhibit fast delayed fluorescence and excellent photoluminescence quantum efficiencies (86 %–97 %). The regular and close stacking of acceptor and donors results in rigidified molecular structures with efficient through-space interaction, which are conducive to suppressing intramolecular motion and reducing reorganized excited-state energy. The organic light-emitting diodes (OLEDs) using them as emitters exhibit excellent electroluminescence performances, with maximum external quantum efficiencies of up to 30.6 %, which is a leading value for the OLEDs based on folded TADF emitters. These results demonstrate the proposed strategy of employing 11,12-dihydroindolo[2,3-a]carbazole as bridge for planar donors and acceptors to construct efficient folded TADF materials is applicable.

Efficient solution-processed ultrapure blue organic light-emitting diodes (OLEDs) have been achieved using non-sensitized multi-resonance emitters. The coordination with two gold-carbene moieties leads to significantly accelerated thermally activated delayed fluorescence (TADF). Meanwhile, the color purity and emission efficiencies of the parental B/N based polycyclic core are essentially unaffected by the gold coordination.

Abstract

Multi-resonance (MR) type emitters have emerged as highly promising candidates for high-resolution organic light-emitting diodes (OLEDs). However, thermally activated delayed fluorescence (TADF) emissions with simultaneous short excited state lifetimes and ultrapure blue color (a CIE_y close to 0.046 and an emission peak >440 nm) have rarely been obtained for MR emitters. Herein, we report a design of dual gold-coordinated MR molecules to achieve efficient and short-lived ultrapure blue TADF emission. The dinuclear Au(I) complex, namely iPrAuBN, shows a narrowband deep-blue emission with a peak maximum of 448 nm and a full width at half maximum (FWHM) of 29 nm in doped film. The coordination with two Au atoms significantly shortens the delayed fluorescence lifetime to 7.8 μs in comparison to 60.6 μs for the parental organic analogue. Solution-processed OLED doped with iPrAuBN demonstrates an ultrapure blue electroluminescence with a peak maximum of 442 nm, a FWHM of 19 nm, CIE coordinates of (0.154, 0.036), and a maximum external quantum efficiency of 14.8 %.

The first reported example of americium circularly polarized luminescence (CPL) is presented. The synthesis of a molecular complex supported by 2-thenoylacetonate and BINAPO yielded a compound that displayed enhanced f-f luminescence thanks to a unique sensitization pathway. This allowed for the detection of CPL despite weak instrumental detection capabilities.

Abstract

The first example of circularly polarized luminescence (CPL) from a molecular americium (Am) complex is reported. Coordination of Am(III) by a combination of thenoyltrifluoroacetonate and a chiral diphosphine oxide ligand yielded a complex with strong sensitized metal-centered luminescence. The energy transfer process for sensitization appears to occur via a unique resonant pathway, which results in the removal of the overlap between ligand phosphorescence and sensitized Am luminescence that has often been observed. Owing to this feature, and despite the limited amount of material that could be used due to the radioactivity of ²⁴¹Am, CPL could be measured. The collected luminescence and CPL spectra provide insight into the crystal field splitting of the ⁵D₁→⁷F₁ transition. These results pave the way for future studies of Am(III) luminescence to investigate electronic structure effects in this and other 5 f elements.

A series of doped polymer-based long-life RTP systems linked to a PVA matrix via thermal annealing was developed. Additionally, by adjusting the doping proportion and annealing time, blue afterglow that lasts for approximately 30 s was achieved. Fortunately, a new type of styrene detector was prepared while the cross-linked network between PVA chains were bridged by 9HMF.

Abstract

Fluorene derivatives have been widely developed in OLEDs because of its efficient fluorescence quantum efficiency, but for which unique rigid biphenyl planar structure and large conjugated system, we hypothesize that they have a great potential for room temperature phosphorescence (RTP) applications, and confirmed this conjecture by subjecting polyvinyl alcohol (PVA) and phosphors to thermal annealing. The cross-linked structure formed during thermal annealing judiciously modulates the phosphorescence emission characteristics of the fluorenol with the synergistic interaction between PVA and fluorenol. Specifically, the lifetime exhibited a substantial increase from 1352.2 ms to 2874.1 ms, accompanied by a quantum yield augmentation from 4.8 % to 11.3 %, which substantiate that cross-linked induced by thermal annealing effectively amplifies the phosphorescent intensity and stability of the phosphors, facilitating ultralong phosphorescent emission at ambient conditions. Furthermore, an effective probe based on this film is developed for its highly sensitive, quantitative and immediate detection of volatile organic compounds. This investigation not only proffers a novel paradigm for the development of advanced RTP materials but also imparts insightful considerations for optimizing the performance of polymers in conjunction with functional materials, encompassing bioimaging, sensing, and optoelectronic devices.

We developed two near-infrared (NIR) radical emitters with record-high photoluminescence quantum efficiency among metal-free organic NIR emitters with emission peaks exceeding 750 nm. The donor-acceptor molecular structure allows the designed radical emitter to exhibit charge-transfer excited state and spatially separated electron and hole levels with non-bonding character. Both the high-frequency and low-frequency vibrations coupling in D₁ are effectively reduced, leading to significantly suppressed non-radiative decay rate. As a result, the “energy gap law” is violated and exceptional luminescence efficiency is achieved.

Abstract

Purely organic molecules exhibiting near-infrared (NIR) emission possess considerable potential for applications in both biological and optoelectronic technological domains, owing to their inherent advantages such as cost-effectiveness, biocompatibility, and facile chemical modifiability. However, the repertoire of such molecules with emission peaks exceeding 750 nm and concurrently demonstrating high photoluminescence quantum efficiency (PLQE) remains relatively scarce due to the energy gap law. Herein, we report two open-shell NIR radical emitters, denoted as DMNA-Cz-BTM and DMNA-PyID-BTM, achieved through the strategic integration of a donor group (DMNA) onto the Cz-BTM and PyID-BTM frameworks, respectively. We found that the donor-acceptor molecular structure allows the two designed radical emitters to exhibit a charge-transfer excited state and spatially separated electron and hole levels with non-bonding characteristics. Thus, the high-frequency vibrations are effectively suppressed. Besides, the reduction of low-frequency vibrations is observed. Collectively, the non-radiative decay channel is significantly suppressed, leading to exceptional NIR PLQE values. Specifically, DMNA-Cz-BTM manifests an emission peak at 758 nm alongside a PLQE of 55 %, whereas DMNA-PyID-BTM exhibits an emission peak at 778 nm with a PLQE of 66 %. Notably, these represent the pinnacle of PLQE among metal-free organic NIR emitters with emission peaks surpassing 750 nm.

Incorporation of B–N Lewis pair functionalized anthracene into a vinylene-linked dimer and polymer leads to selective extension of the lowest unoccupied molecular orbital (LUMO), thus significantly lowering the band gap, shifting the emission into the near-infrared region, and modulating the self-sensitized reactivity toward oxygen and release of singlet oxygen from the corresponding endoperoxides.

Abstract

Acenes are attractive as building blocks for low gap organic materials with applications, for example, in organic light emitting diodes, solar cells, bioimaging and diagnostics. Previously, we have shown that modification of dipyridylanthracene via B–N Lewis pair fusion (BDPA) strongly redshifts the emission, while facilitating self-sensitized reactivity toward O₂ to reversibly generate the corresponding endoperoxides. Herein, we report on the further expansion of the π-system of BDPA to a vinyl-substituted monomer, vinylene-bridged dimer, and a polymer with an average of 20 chromophores. The extension of π-conjugation results in largely reduced band gaps of 1.8 eV for the dimer and 1.7 eV for the polymer, the latter giving rise to NIR emission with a maximum at 731 nm and an appreciable quantum yield of 7 %. Electrochemical and computational studies reveal efficient delocalization of the lowest unoccupied molecular orbital (LUMO) along the pyridyl-anthracene-pyridyl axis, which results in effective electronic communication between BDPA units, selectively lowers the LUMO, and ultimately narrows the band gap. Time-resolved emission and transient absorption (TA) measurements offer insights into the pertinent photophysical processes. Extension of π-conjugation also slows down the self-sensitized formation of endoperoxides, while significantly accelerating the thermal release of singlet oxygen to regenerate the parent acenes.

Reversible binding of donor-acceptor pairs in solid state materials by light-manipulated charge transfer and electron transfer has been achieved, accompanied by visual color switching and fluorescence on-off as output signals.

Abstract

Modulating charge transfer (CT) interactions between donor and acceptor molecules may give rise to unique dynamic changes in physicochemical properties, exhibiting great importance in supramolecular chemistry and materials science. In this work, we demonstrate the first instance of reversible photomodulation of donor-acceptor (D−A) CT interaction in the solid state. Pyridinium-based chromophore featuring π-conjugated D−A structures can not only function as a good electron acceptor to undergo photoinduced electron transfer (ET) or engage in intermolecular CT interaction, but also exhibit unique dual emission depending on the excitation wavelengths. The rotatable C−C single bonds within D−A pairs enhance the tunability of molecular structure. Through the synergy of a photoinduced ET and an excited-state conformational change, the intermolecular CT interaction can be switched on and off by alternate light irradiation to enable reversibly modulation of the affinity between donor and acceptor molecules, accompanied by visual color switching and fluorescence on-off as feedback signals.

Based on Clar's aromatic π-sextet rule, we have successfully constructed the first red π-extended multiple resonance (MR) emitter by substituting the conventional benzene ring core with anthracene. The corresponding narrowband red (luminescence wavelength: 608 nm) organic light-emitting diode exhibits a high external quantum efficiency of 27.3 %, with only a slight decrease of 3.7 % at an elevated luminance level of 100,000 cd/m².

Abstract

Despite the proliferation of multiple resonance (MR) materials in the blue to green spectral ranges, red MR emitters remain scarce in the literature, an area that certainly warrants attention for future applications. Here, through a clever application of classic Clar's aromatic π-sextet rule, we triumphantly constructed the first red MR emitter by substituting the conventional benzene ring core with anthracene (fewer π-sextets). Theoretical studies indicate that the quantity of π-sextets ultimately determines the optical band gap of a molecule, rather than the number of fused benzene rings. Benefiting from the high photoluminescence quantum yield of ~94 % and horizontal dipole ratio of ~90 %, the corresponding narrowband red (luminescence wavelength: 608 nm) organic light-emitting diode shows a high external quantum efficiency of 27.3 %, with only a slight decrease of 3.7 % at an elevated luminance level of 100,000 cd/m².

Biprotonated (R/S-LH2)ZnX₄ and monoprotonated (R/S-LH1)₂ZnX₄ (X=Cl, Br) were constructed from a single chiral organic cation. The reversible structural transformation induced by polar solvents and HBr/heat engenders chiroptical switching behaviors. The structural design strategy developed in this work elucidates the structure-property mechanism underlying the structural transitions and the distortion-related chirality transfer.

Abstract

Precise control over the organic composition is crucial for tailoring the distinctive structures and properties of hybrid metal halides. However, this approach is seldom utilized to develop materials that exhibit stimuli-responsive circularly polarized luminescence (CPL). Herein, we present the synthesis and characterization of enantiomeric hybrid zinc bromides: biprotonated ((R/S)-C₁₂H₁₆N₂)ZnBr₄ ((R/S-LH2)ZnBr₄) and monoprotonated ((R/S)-C₁₂H₁₅N₂)₂ZnBr₄ ((R/S-LH1)₂ZnBr₄), derived from the chiral organic amine (R/S)-2,3,4,9-Tetrahydro-1H-carbazol-3-amine ((R/S)-C₁₂H₁₄N₂). These compounds showcase luminescent properties; the zero-dimensional biprotonated form emits green light at 505 nm, while the monoprotonated form, with a pseudo-layered structure, displays red luminescence at 599 and 649 nm. Remarkably, the reversible local protonation-deprotonation behavior of the organic cations allows for exposure to polar solvents and heating to induce reversible structural and luminescent transformations between the two forms. Theoretical calculations reveal that the lower energy barrier associated with the deprotonation process within the pyrrole ring is responsible for the local protonation-deprotonation behavior observed. These enantiomorphic hybrid zinc bromides also exhibit switchable circular dichroism (CD) and CPL properties. Furthermore, their chloride counterparts were successfully obtained by adjusting the halogen ions. Importantly, the unique stimuli-responsive CPL characteristics position these hybrid zinc halides as promising candidates for applications in information storage, anti-counterfeiting, and information encryption.

Taking advantage of both the unique structural and chiral features of molecular [c2]daisy chain, the first circularly polarized luminescence switch based on chiral molecular muscle has been successfully constructed, not only successfully widening the application scopes of molecular muscles, but also providing a promising platform for the construction of novel smart chiral luminescent materials for practical applications.

Abstract

Aiming at the further extension of the application scope of traditional molecular muscles, a novel bispyrene-functionalized chiral molecular [c2]daisy chain was designed and synthesized. Taking advantage of the unique dimeric interlocked structure of molecular [c2]daisy chain, the resultant chiral molecular muscle emits strong circularly polarized luminescence (CPL) attributed to the pyrene excimer with a high dissymmetry factor (g _lum) value of 0.010. More importantly, along with the solvent- or anion- induced motions of the chiral molecular muscle, the precise regulation of the pyrene stacking within its skeleton results in the switching towards either “inversed” state with sign inversion and larger g _lum values or “down” state with maintained handedness and smaller g _lum values, making it a novel multistate CPL switch. As the first example of chiral molecular muscle-based CPL switch, this proof-of-concept study not only successfully widens the application scopes of molecular muscles, but also provides a promising platform for the construction of novel smart chiral luminescent materials for practical applications.

A highly crystalline self-assembled multilayer (SAMUL) that is fundamentally different from the conventional monolayer or disordered bilayer used for hole-extraction in inverted perovskite solar cells (PSCs). A detailed structure-property-performance relationship of molecules used for SAMUL is established through a systematic study of their crystallinity, molecular packing, and hole-transporting properties. The CbzNaphPPA-based SAMUL with the highest crystallinity and hole mobility derived from the ordered H-aggregation, which resulted in a very impressive power conversion efficiency (PCE) of 26.07 %. Additionally, a record-high PCE of 23.50 % could be achieved by adopting a thermally evaporated SAMUL. This greatly simplifies and broadens the scope for SAM to be used for large-area devices on diverse substrates.

Abstract

We report a highly crystalline self-assembled multilayer (SAMUL) that is fundamentally different from the conventional monolayer or disordered bilayer used for hole-extraction in inverted perovskite solar cells (PSCs). The SAMUL can be easily formed on ITO substrate to establish better surface coverage to enhance the performance and stability of PSCs. A detailed structure-property-performance relationship of molecules used for SAMUL is established through a systematic study of their crystallinity, molecular packing, and hole-transporting properties. These SAMULs are rationally optimized by varying their molecular structures and deposition methods through thermal evaporation or spin-coating for fabricating PSCs. The CbzNaphPPA-based SAMUL was chosen for fabricating inverted PSCs due to it exhibiting the highest crystallinity and hole mobility which is derived from the ordered H-aggregation. This resulted in a remarkably high fill factor of 86.45 %, which enables a very impressive power conversion efficiency (PCE) of 26.07 % to be achieved along with excellent device stability (94 % of its initial PCE retained after continuous operation for 1200 h under 1-sun irradiation at maximum power point at 65 °C). Additionally, a record-high PCE of 23.50 % could be achieved by adopting a thermally evaporated SAMUL. This greatly simplifies and broadens the scope for SAM to be used for large-area devices on diverse substrates.

A solution-processable thermally activated delayed fluorescence (TADF) molecule with an improved horizontal emitting dipole orientation, fast reverse intersystem crossing, and high photoluminescence quantum yield in a pristine film was constructed. The solution-processable non-doped device and the TADF-sensitized fluorescence device exhibited maximum external quantum efficiencies of 32.6 % and 30.7 %, respectively, and alleviated efficiency roll-off.

Abstract

Thermally activated delayed fluorescence (TADF) emitters with a high horizontal orientation are highly essential for improving the external quantum efficiency (EQE) of organic light-emitting diodes; however, pivotal molecular design strategies to improve the horizontal orientation of solution-processable TADF emitters are still scarce and challenging. Herein, a phenyl bridge is adopted to connect the double TADF units, and generate a dimerized TADF dendrimer, D4CzBNPh-SF. Compared to its counterpart with a single TADF unit, the proof-of-the-concept molecule not only exhibits an improved horizontal dipole ratio (78 %) due to the π-delocalization-induced extended molecular conjugation, but also displays a faster reversed intersystem crossing rate constant (6.08×10⁶ s⁻¹) and a high photoluminescence quantum yield of 95 % in neat film. Consequently, the non-doped solution-processed device with D4CzBNPh-SF as the emitter achieves an ultra-high maximum EQE of 32.6 %, which remains at 26.6 % under a luminance of 1000 cd/m². Furthermore, when using D4CzBNPh-SF as a sensitizer, the TADF-sensitized fluorescence device exhibits a high maximum EQE of 30.7 % at a luminance of 575 cd/m² and a full width at half maximum of 36 nm.

Two dimerized small-molecule acceptors (DYTVT and DYTCVT) with tailored linker structures are developed. Organic solar cells using DYTVT and DYTCVT as alloy-acceptors exhibit high power conversion efficiency (PCE) of 18.4% and excellent photostability (t _80% lifetime > 4,200 h under 1-Sun illumination).

Abstract

High power conversion efficiency (PCE) and long-term stability are prerequisites for commercialization of organic solar cells (OSCs). Herein, two dimer acceptors (DYTVT and DYTCVT) are developed with different properties through linker engineering, and study their effects as alloy-like acceptors on the photovoltaic performance and photostability of OSCs. These ternary OSCs effectively combine the advantages of both dimer acceptors. DYTVT, characterized by its high backbone planarity, ensures elevated electron mobility and high glass-transition temperature (T _g), leading to efficient charge transport and enhanced photostability of OSCs. Conversely, DYTCVT, with its significant dipole moment and electrostatic potential, enhances compatibility of the alloy acceptors with donors and refines the blend morphology, facilitating efficient charge generation in OSCs. Consequently, D18:DYTVT:DYTCVT OSCs exhibit higher PCE (18.4%) compared to D18:MYT (monomer acceptor, PCE = 16.5%), D18:DYTVT (PCE = 17.4%), and D18:DYTCVT (PCE = 17.0%) OSCs. Furthermore, owing to higher T _g of alloy acceptors (133 °C) than MYT (T _g = 80 °C) and DYTCVT (T _g = 120 °C), D18:DYTVT:DYTCVT OSCs have significantly higher photostability (t _80% lifetime = 4250 h under 1-sun illumination) compared to D18:MYT (t _80% lifetime = 40 h) and D18:DYTCVT OSCs (t _80% lifetime = 2910 h).

A NIR-II emissive neutral merocyanine dye is developed based on the clinically used ionic indocyanine green, exhibiting maintained strong near-infrared absorption, improved photostability, enhanced photothermal performance, bright NIR-II emission, and specific tumor accumulation. The mCy890 NPs are successfully utilized for efficient in vivo NIR-II fluorescence bioimaging and cancer phototheranostics.

Abstract

Fluorescence imaging (FLI)-guided phototheranostics using emission from the second near-infrared (NIR-II) window show significant potential for cancer diagnosis and treatment. Clinical imaging-used polymethine ionic indocyanine green (ICG) dye is widely adopted for NIR fluorescence imaging-guided photothermal therapy (PTT) research due to its exceptional photophysical properties. However, ICG has limitations such as poor photostability, low photothermal conversion efficiency (PCE), short-wavelength emission peak, and liver-targeting issues, which restrict its wider use. In this study, two ionic ICG derivatives are transformed into neutral merocyanines (mCy) to achieve much-enhanced performance for NIR-II cancer phototheranostics. Initial designs of two ionic dyes show similar drawbacks as ICG in terms of poor photostability and low photothermal performance. One of the modified neutral molecules, mCy890, shows significantly improved stability, an emission peak over 1000 nm, and a high photothermal PCE of 51%, all considerably outperform ICG. In vivo studies demonstrate that nanoparticles of the mCy890 can effectively accumulate at the tumor sites for cancer photothermal therapy guided by NIR-II fluorescence imaging. This research provides valuable insights into the development of neutral merocyanines for enhanced cancer phototheranostics.

In this study, an energy-efficient, green and economically scalable protocol for the synthesis of para-Azaquinodimethane small molecules is reported. In thin film, excitation of anisole derivatives leads to ultrafast and quantitative FRET sensitization of bithiophene SF-active molecules. The synergy between FRET and SF for the first time at the intermolecular level in the solid state with unconventional SF chromophores is exploited.

Abstract

In this work, a green protocol for the synthesis of new para-Azaquinodimethane (pAQM) small molecules, functionalized with anisole (An) or bithiophene (TT) moieties on the central unit and with different alkoxy groups as lateral substituents is developed and reported. The alkoxy lateral substituents are found to strongly impact the solubility and processability of the chromophores. On the other hand, the steady–state and time-resolved spectroscopic results show completely different spectral and photophysical features for the An- and TT- derivatives. Only for the TT-compounds, the nanosecond and femtosecond transient absorption experiments reveal low efficiency of triplet production in solution as well as ultrafast (≈1 ps) and efficient (≈200%) singlet fission (SF) in thin film. The yellow An-containing molecules are instead used to sensitize the purple SF-active TT-compounds via quantitative FRET in mixed thin films, which interestingly exhibit panchromatic absorption extending in the entire visible spectral range. With this study, the synergy between FRET and SF is exploited at the intermolecular level in the solid-state for the first time by considering unconventional and stable SF chromophores, opening intriguing new possibilities for solar energy harvesting.

Publication date: 15 July 2024

Source: Chemical Engineering Journal, Volume 492

Author(s): Lifen Chen, Mingjia Deng, Shao-Yun Yin, Yu Fu, Yingxiao Mu, Jia-Xiong Chen, Lingyun Cui, Shaomin Ji, Yanping Huo, Hao-Li Zhang

We synthesized four chiral molecular tubes by condensing enantiomerically pure trans-cyclohexane-1,2-diamine with luminescent tetraformyl precursors. Within the framework of these tubes, the stereochirality of the bisamino building blocks was transferred and amplified, leading to planar chirality of the tubes. These tubes thus demonstrate a promising approach to CPL-active materials.

Abstract

Here, we successfully synthesized four structurally analogous, self-assembled chiral molecular tubes with relatively high yields. This achievement involved the condensation of six equivalents of enantiomerically pure trans-cyclohexane-1,2-diamine (trans-CHDA) and three equivalents of the corresponding tetraformyl precursor. Each precursor was equipped with a luminescent linker terminated by two m-phthalaldehyde units. Even though these tetraformyl precursors are barely soluble in almost all organic solvents, the molecular tubes are highly soluble in nonpolar solvents such as chloroform, allowing us to fully characterize them in solution. The stereo-chirality of the chiral bisamino building blocks endows the frameworks of molecular tubes with planar chirality. As a consequence, all of these molecular tubes exhibit circularly polarized luminescence (CPL) with relatively large dissymmetry values |g _lum| up to 7×10⁻³, providing an efficient method for synthesizing CPL-active materials.

Efficient blue carbonyl-nitrogen (CO-N) multi-resonance thermally activated delayed fluorescence (MR-TADF) materials are developed by introducing bulky substituents to a planar CO-N MR-TADF core constructed by fusing carbonyl groups with carbazole, and blue hyperfluorescence organic light-emitting diodes with the state-of-the-art electroluminescence (EL) efficiencies and narrow EL spectra are fabricated.

Abstract

Efficient blue multi-resonance thermally activated delayed fluorescence (MR-TADF) materials are highly desired for the fabrication of organic light-emitting diodes (OLEDs) with high color purity. But only very limited carbonyl-nitrogen (CO-N) blue MR-TADF are well-developed. Herein, two new blue CO-N MR-TADF molecules (tBuPQCZ and 2tBuPQCZ) are explored by introducing bulky substituents to a planar CO-N MR-TADF core constructed by fusing carbonyl groups with carbazole, and their thermal stability, electronic structures, and photophysical properties are investigated. They exhibit blue photoluminescence (PL) peaks at 451 and 447 nm, and narrow full width at half maximums (FWHMs) of 26 and 25 nm in toluene. In doped films, they exhibit strong blue emissions with PL peaks at 474 and 469 nm, FWHMs of 51 and 49 nm, and satisfactory PL quantum yields of 80% and 72%. Moreover, blue OLEDs using them as emitters exhibit excellent external quantum efficiencies (EQEs) of 20.4% and 21.5%, and the hyperfluorescence OLEDs based on them provide state-of-the-art EQEs of 30.1% and 29.0% with small FWHMs of 34 and 32 nm and Commission Internationale de I'Eclairage coordinates of (0.136, 0.134) and (0.141, 0.105). The insights gained in this work should be valuble for the development of efficient blue CO-N MR-TADF materials.