Search

Abstract Thermally activated delayed fluorescence (TADF) materials have numerous applications in energy conversion and luminescent imaging. However, they are typically achieved as metal‐organic complexes or pure organic molecules. Herein, we report the largest Au‐Ag‐oxo nanoclusters to date, Au18Ag26(R1COO)12(R2C≡C)24(μ4‐O)2(μ3‐O)2 (Au18Ag26, where R1 = CH3‐, Ph‐, CHOPh‐ or CF3Ph‐; R2 = Ph‐ or FPh‐). These nanoclusters exhibit exceptional TADF properties, including a small S1‐T1 energy gap of 55.5 meV, a high absolute photoluminescence quantum yield of 86.7%, and a microseconds TADF decay time of 1.6 μs at ambient temperature. Meanwhile, Au18Ag26 shows outstanding stability against oxygen quenching and ambient conditions. Atomic level analysis reveals the strong π⋯π and C‐H⋯π interactions from the aromatic alkynyl ligands and the enhancement of metal‐oxygen‐metal interactions by centrally coordinated O2−. Modeling of the electronic structure shows spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital, which promote charge transfer from the ligand shell, predominantly carboxylate ligands, to O2−‐embedded metal core. Furthermore, TADF Au‐Ag‐oxo nanoclusters exhibit promising radioluminescence properties, which we demonstrate for X‐ray imaging. Our work paves the way for the design of TADF materials based on large metal nanoclusters for light‐emission and radioluminescence applications.

The design and synthesis of four twisted donor‐acceptor (D‐A) thermally activated delayed fluorescence (TADF) molecules CBZ‐IQ, CBZ‐2FIQ, DI‐IQ and DI‐2FIQ is reported in this work based on diindolocarbazole (DI) and phenyl carbazole as donor and indoloquinoxalines as acceptor. These compounds serve as photocatalysts for organic transformations. Theoretical calculations and experimental data showed reasonable singlet and triplet energy gaps of 0.17‐0.26 eV for all compounds. All molecules showed increase in fluorescence quantum yields after degassing the solution and the transient photoluminescence decay showed two components: shorter prompt components (11.4 ns to 31 ns) and longer delayed components (36.4 ns to 1.5 μs) which further indicate the occurrence of TADF process. Cyclic voltammetry studies indicated well‐suited excited state redox potentials of all compounds to catalyze organic transformations such as heteroarene arylation. Accordingly, photocatalytic C−H arylation of heteroarenes were performed using these compounds with excellent isolated yields of upto 80 %. Due to their suitable efficient triplet energy levels, all the emitters were also employed as energy transfer photocatalysts in E to Z isomerization of stilbene with the excellent conversion of ~90 %. [ABSTRACT FROM AUTHOR]

Living system involves a plenty of delicate processes where a tiny structural variation of biological substance may lead to drastic change of the fate of the living system. Inspired by this, in artificial photofunctional systems, if tiny structural variation changes the fate of excited states, a new class of advanced material would emerge for optical analysis, sensing, and next‐generation display is reasoned. However, such delicate processes remain rarely explored in photofunctional systems, especially in room temperature organic afterglow systems. Here the attachment/detachment of methoxy group can switch off/on twisted intramolecular charge transfer property in difluoroboron β‐diketonate systems is reported. In addition, structural isomerization triggers afterglow transformation from room temperature phosphorescence to thermally activated delayed fluorescence. These observations are helpful for better photophysical understanding on luminescence systems and advanced material design. [ABSTRACT FROM AUTHOR]

Luminescent metal complexes based on earth abundant elements are a valuable target to substitute 4d/5d transition metal complexes as triplet emitters in advanced photonic applications. Whereas CuI complexes have been thoroughly investigated in the last two decades for this purpose, no structure‐property‐relationships for efficient luminescence involving triplet excited states from ZnII complexes are established. Herein, we report on the design of monomeric carbene zinc(II) dithiolates (CZT) featuring a donor‐acceptor‐motif that leads to highly efficient thermally activated delayed fluorescence (TADF) with for ZnII compounds unprecedented radiative rate constants kTADF=1.2×106 s−1 at 297 K. Our high‐level DFT/MRCI calculations revealed that the relative orientation of the ligands involved in the ligand‐to‐ligand charge transfer (1/3LLCT) states is paramount to control the TADF process. Specifically, a dihedral angle of 36–40° leads to very efficient reverse intersystem‐crossing (rISC) on the order of 109 s−1 due to spin‐orbit coupling (SOC) mediated by the sulfur atoms in combination with a small ΔES1‐T1 of ca. 56 meV. [ABSTRACT FROM AUTHOR]

This study proposes a novel approach to develop highly efficient, narrow‐emitting violet materials based on boron and oxygen polycyclic aromatic hydrocarbon multiple resonance structure. Herein, B‐2OCz is developed by fusing indole with a 5,9‐dioxa‐13bboranaphtho[3,2,1‐de]anthracene (DOBNA) core to enhance its thermally activated delayed fluorescence (TADF) properties and molecular rigidity. On the other hand, the B‐2OCz‐Si is decorated with a bulky tetraphenylsilyl substituent. B‐2OCz‐Si exhibits exceptional features such as violet emission at 397 nm, a very small full width at half maximum of 16 nm, and 82% of photoluminescence quantum yield. The B‐2OCz‐Si devices achieve a high external quantum efficiency of over 15%, violet emission with a peak wavelength of 423 nm, and color coordinates of (0.156, 0.037). Furthermore, the B‐2OCz‐Si is used as an electron transport type host material for phosphorescent organic light‐emitting diodes (PhOLEDs), based on its high triplet energy and TADF properties. As compared to the conventional triazine based host materials, these newly developed DOBNA‐based materials display superior device lifetime performance. All these potential aspects corroborate that this new class of DOBNA‐based materials can work as a promising host material for PhOLEDs and violet‐emitting fluorescent devices. [ABSTRACT FROM AUTHOR]

This research focuses on a theoretical study of diphenylsulfone-based emitters for thermally activated delayed fluorescence (TADF). The acceptor moiety employed in this study is sulfonyldibenzene, while the donor moiety is 9H-carbazole. The effects of methoxy, thiophene, pyridine, and pyrazine adding on the donor moiety were investigated, resulting in the design of six distinct molecules. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, utilizing the B3LYP functional with 6-311G(d,p) basis sets, were used to assess the properties of these compounds in their singlet, doublet, and triplet states. The calculations encompassed various aspects, including ground state molecular geometry, electronic properties, dipole moments, polarizabilities, frontier orbital energies, density of states, UV-Vis spectra, and IR spectra. The investigation revealed that adding the donor moiety with rings, particularly thiophene and pyridine, resulted in improved properties, including molecular geometry. Furthermore, increasing the D-A dihedral angle was found to increase the energy gap, optical gap, dipole moments, and polarizabilities, while reducing the ∆EST and the overlap between the HOMO and LUMO. Hole-electron analysis demonstrated that all the compounds exhibited localized excitation characteristics, with the electrons being photoinduced locally. These compounds exhibited strong blue emissions, with maximum wavelengths ranging from 387.462 to 458.286 nm in the singlet-triplet states. Moreover, the designed compounds exhibited coverage of the entire visible region in their UV-Vis spectra when in the doublet state. Based on these findings, these compounds show promise as TADF emitters in organic light-emitting diodes (OLEDs), providing improvements in efficiency and properties. [ABSTRACT FROM AUTHOR]

The fabrication of optoelectronic devices using low‐cost inkjet printing techniques is a topic of great interest to the scientific and industrial community and represents a step toward the full deployment of solution‐processable organic light emitting diodes (OLEDs), particularly for commercial lighting and signaling applications. Herein, the inkjet printing of tBuCzDBA (9,10‐bis(4‐(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)−2,6‐dimethylphenyl)−9,10‐diboraanthracene) is reported, a high‐performing thermally activated delayed fluorescence (TADF) emitter for OLEDs. Optimizing the surface tension values of the ink formulations and the associated wetting behavior are crucial parameters for achieving a uniform and homogeneous printed thin film. In particular, it is observed that using a proper mixture of solvents with different surface tensions, it is possible to generate Marangoni flows inside the drop, which triggers a very fast drying process, ensuring optimized morphological and optical properties in the inkjet printed tBuCzDBA‐based film. OLEDs exploiting this film as an emissive layer are then fabricated, achieving a maximum luminance of 32 000 cd m−2, a current efficiency of 27.5 cd A−1, and an external quantum efficiencyof 10%. To the best of the knowledge, this is the highest efficiency reported to date for self‐hosted TADF inkjet‐printed OLEDs. [ABSTRACT FROM AUTHOR]

Understanding the host‐guest interactions for thermally activated delayed fluorescence (TADF) emitters is critical because the interactions between the host matrices and TADF emitters enable precise control on the optoelectronic performance, whereas technologically manipulating the singlet and triplet excitons by using different kinds of host‐guest interactions remains elusive. Here, we report a comprehensive picture that rationalizes host‐guest interaction‐modulated exciton recombination by using time‐resolved spectroscopy. We found that the early‐time relaxation is accelerated in polar polymer because dipole‐dipole interaction facilitates the stabilization of the 1CT state. However, an opposite trend is observed in longer delay time, and faster decay in the less polar polymer is ascribed to the π‐π interaction that plays the dominant role in the later stage of the excited state. Our findings highlight the technological engineering singlet and triplet excitons using different kinds of host‐guest interactions based on their electronic characteristics. [ABSTRACT FROM AUTHOR]

Carbazole‐triazine dendrimers with a bulky terminal substituent were synthesized, and the thermally activated delayed fluorescence (TADF) property was investigated. Compared to unsubstituted carbazole dendrimers, dendrimers with bulky terminal substituents showed comparable to better photoluminescence quantum yields (PLQY) in neat films. Phenylfluorene (PF)‐substituted dendrimers showed the highest PLQY of 81%, a small ΔEst of 0.06 eV, and the fastest reverse intersystem crossing (RISC) rate of ∼1 × 105 s−1 compared to other dendrimers. Phosphorescence measurements of dendrimers and dendrons (fragments) indicate that the close proximity of the triplet energy of phenylfluorene‐substituted carbazole dendrons (3LE) to that of phenylfluorene‐substituted dendrimers (1CT, 3CT) contributes to RISC promotion and improves TADF efficiency. Terminal modification fine‐tunes the energy level and suppresses intermolecular interactions, and this study provides a guideline for designing efficient solution‐processable and non‐doped TADF materials. [ABSTRACT FROM AUTHOR]

Efficient ultraviolet (UV) electroluminescent materials remain a great challenge, since short peak wavelength <400 nm and narrow full width at half maximum (FWHM) <50 nm are simultaneously required. In this sense, multi‐resonance (MR) thermally activated delayed fluorescence (TADF) emitters featuring narrow‐band emissions hold the promise for UV applications. Herein, a novel MR‐TADF skeleton featuring carbazole‐phosphine oxide (P=O) fused aromatics is developed to construct the first two UV MR emitters named CzP2PO and tBCzP2PO. In addition to synergistic resonance effects of P=O and N atom, sp3‐hybrid P atom renders the curved polycyclic planes of CzP2PO and tBCzP2PO, giving rise to their narrowband UV emissions with peak wavelengths <390 nm and FWHM<35 nm. Besides configuration quasi‐planarization for radiation enhancement and quenching suppression, P=O moiety further enhances singlet‐triplet coupling to facilitate reverse intersystem crossing, resulting in the state‐of‐the‐art photoluminescence quantum yield of 62 % in tBCzP2PO doped films. As consequence, tBCzP2PO endowed its UV organic light‐emitting diodes with the peak at 382 nm and FWHM of 32 nm, and especially the record‐high external quantum efficiency (EQE) of 15.1 % among all kinds of UV devices. Our results demonstrate great potential of P=O based MR emitters in practical applications including optoelectronics, biology and medicine science. [ABSTRACT FROM AUTHOR]

The emerging research area of ultrasmall, luminescent coinage metal nanoclusters exhibiting delayed emission through thermally-activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) has garnered considerable interest in diverse applications such as imaging, therapy, and optoelectronics. To utilize the metal nanoclusters for advanced applications, it is crucial to understand the excited state dynamics governing delayed emission. Here, we comprehensively review the recent advancement in the design strategies of metal nanoclusters aimed at achieving control over their long-lived luminescence. The design strategies include solvent-induced aggregation, crystallization-induced self-assembly, complexation methods, ligand engineering, metal core doping, and composition regulation. Through these strategies, long-lived emission can be achieved which can provide TADF and RTP luminescence mechanism. Our primary goal is to harness the versatile capabilities of long-lived metal nanoclusters to advance their optoelectronic properties and broaden their range of practical applications. [ABSTRACT FROM AUTHOR]

The investigation of organic light‐emitting diodes (OLEDs) and organic laser devices with thermally activated delayed fluorescence (TADF) molecules is emerging due to the potential of harnessing triplets. In this work, a boron/nitrogen multiple‐resonance TADF polycyclic framework fusing carbazole units (CzBNPh) was proposed. CzBNPh exhibited a narrowband emission (<30 nm), a unity photoluminescence quantum yield, and a fast radiative rate. Consequently, CzBNPh demonstrated a low distributed feedback (DFB) lasing threshold of 0.68 μJ cm−2. Furthermore, the stimulated emission zone of CzBNPh was effectively separated from its singlet and triplet absorption, thereby minimizing the singlet‐triplet annihilation under long‐pulsed excitation ranging from 20 μs to 2.5 ms. Significantly, the enhanced rigid molecular conformation, thermal stability, and photo‐stability resulted in improved lasing and electroluminescence stability compared to that of 5,9‐diphenyl‐5,9‐diaza‐13b‐boranaphtho[3,2,1‐de]anthracene (DABNA)‐core. These findings indicate the potential of CzBN‐core as a promising framework for achieving long‐pulsed wave and electrically‐pumped lasing in the future. [ABSTRACT FROM AUTHOR]

A crystalline host matrix (CHM) with embedded nanoaggregates (NA) is a powerful strategy to develop high‐performance crystalline OLEDs that can combine the advantages of both crystalline and high‐exciton‐utilization‐efficiency light emitting materials. Here a CHM‐NA structure blue‐emission crystalline OLED is developed, which employs a thermally activated delayed fluorescence (TADF) material. The CHM‐TADFNA OLED is proved to efficiently manage exciton distribution by engineering nanoaggregates. The device exhibits a remarkable EQE up to 10.4% and achieves the characteristics of rapid turn‐on, and fast ramping of luminance and current density, resulting in an enhanced photon output and a lower series‐resistance Joule‐heat loss ratio, indicating a competitive pathway to future blue‐emission OLEDs. [ABSTRACT FROM AUTHOR]

B‐ and N‐embedded multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters usually suffer from slow reverse intersystem crossing (RISC) process and aggregation‐caused emission quenching. Here, we report the design of a sandwich structure by placing the B−N MR core between two electron‐donating moieties, inducing through‐space charge transfer (TSCT) states. The proper adjusting of the energy levels brings about a 10‐fold higher RISC rate in comparison with the parent B−N molecule. In the meantime, a high photoluminescence quantum yield of 91 % and a good color purity were maintained. Organic light‐emitting diodes based on the new MR emitter achieved a maximum external quantum efficiency of 31.7 % and small roll‐offs at high brightness. High device efficiencies were also obtained for a wide range of doping concentrations of up to 20 wt % thanks to the steric shielding of the B−N core. A good operational stability with LT95 of 85.2 h has also been revealed. The dual steric and electronic effects resulting from the introduction of a TSCT state offer an effective molecular design to address the critical challenges of MR‐TADF emitters. [ABSTRACT FROM AUTHOR]

The prediction of the metal cluster within a coordination polymer or complex, as well as the dimensionality of the resulting polymer or complex (i.e., 0D, 1D, 2D, or 3D), is often challenging. This is the case for Ph2P(CH2)mPPh2 ligands (1 ≤ m ≤ 8) and CuX salts, particularly for X = I. This work endeavors a systematic statistical analysis combining studies in the literature and new data, mapping the nature of the resulting CuI aggregates with eight different diphoshphines in 2:1, 3:2, 1:1, 2:3, and 1:2 CuI:Ph2P(CH2)mPPh2 molar ratios as a function of m, which lead to either pure products or mixtures. Several trends are made relating stoichiometry and chain length to the CuI cluster formed (i.e., globular vs. quasi-planar). Four new X-ray structures were determined: [Cu3I2(L1)3]I, Cu3I3(L2)2, Cu2I2(L6)2, and Cu4I4(L8)2, where m is, respectively, 1, 2, 6, and 8, in which the CuxIy central aggregates adopt triangular bipyramid, diamond, rhomboid, and cubane shaped motifs, respectively. Photophysical measurements assisted the establishment of trends considering the paucity of the crystallographic structures. During this study, it was also found that the 0D-complex Cu2I2(Ph2P(CH2)5PPh2)2 exhibits thermally activated delayed fluorescence. [ABSTRACT FROM AUTHOR]

A series of 1,8-naphthalimide (NI)-phenothiazine (PTZ) electron donor–acceptor dyads were prepared to study the thermally activated delayed fluorescence (TADF) properties of the dyads, from a point of view of detection of the various transient species. The photophysical properties of the dyads were tuned by changing the electron-donating and the electron-withdrawing capability of the PTZ and NI moieties, respectively, by oxidation of the PTZ unit, or by using different aryl substituents attached to the NI unit. This tuning effect was manifested in the UV–vis absorption and fluorescence emission spectra, e.g., in the change of the charge transfer absorption bands. TADF was observed for the dyads containing the native PTZ unit, and the prompt and delayed fluorescence lifetimes changed with different aryl substituents on the imide part. In polar solvents, no TADF was observed. For the dyads with the PTZ unit oxidized, no TADF was observed as well. Femtosecond transient absorption spectra showed that the charge separation takes ca. 0.6 ps, and admixtures of locally excited (3LE) state and charge separated (1CS/3CS) states formed (in n-hexane). The subsequent charge recombination from the 1CS state takes ca. 7.92 ns. Upon oxidation of the PTZ unit, the beginning of charge separation is at 178 fs and formation of 3LE state takes 4.53 ns. Nanosecond transient absorption (ns-TA) spectra showed that both 3CS and 3LE states were observed for the dyads showing TADF, whereas only 3LE or 3CS states were observed for the systems lacking TADF. This is a rare but unambiguous experimental evidence that the spin–vibronic coupling of 3CS/3LE states is crucial for TADF. Without the mediating effect of the 3LE state, no TADF is resulted, even if the long-lived 3CS state is populated (lifetime τCS ≈ 140 ns). This experimental result confirms the 3CS → 1CS reverse intersystem crossing (rISC) is slow, without coupling with an approximate 3LE state. These studies are useful for an in-depth understanding of the photophysical mechanisms of the TADF emitters, as well as for molecular structure design of new electron donor–acceptor TADF emitters.

Abstract Carbazole‐triazine dendrimers with a bulky terminal substituent were synthesized, and the thermally activated delayed fluorescence (TADF) property was investigated. Compared to unsubstituted carbazole dendrimers, dendrimers with bulky terminal substituents showed comparable to better photoluminescence quantum yields (PLQY) in neat films. Phenylfluorene (PF)‐substituted dendrimers showed the highest PLQY of 81%, a small ΔEst of 0.06 eV, and the fastest reverse intersystem crossing (RISC) rate of ∼1 × 105 s−1 compared to other dendrimers. Phosphorescence measurements of dendrimers and dendrons (fragments) indicate that the close proximity of the triplet energy of phenylfluorene‐substituted carbazole dendrons (3LE) to that of phenylfluorene‐substituted dendrimers (1CT, 3CT) contributes to RISC promotion and improves TADF efficiency. Terminal modification fine‐tunes the energy level and suppresses intermolecular interactions, and this study provides a guideline for designing efficient solution‐processable and non‐doped TADF materials.

Abstract Understanding the host‐guest interactions for thermally activated delayed fluorescence (TADF) emitters is critical because the interactions between the host matrices and TADF emitters enable precise control on the optoelectronic performance, whereas technologically manipulating the singlet and triplet excitons by using different kinds of host‐guest interactions remains elusive. Here, we report a comprehensive picture that rationalizes host‐guest interaction‐modulated exciton recombination by using time‐resolved spectroscopy. We found that the early‐time relaxation is accelerated in polar polymer because dipole‐dipole interaction facilitates the stabilization of the 1CT state. However, an opposite trend is observed in longer delay time, and faster decay in the less polar polymer is ascribed to the π‐π interaction that plays the dominant role in the later stage of the excited state. Our findings highlight the technological engineering singlet and triplet excitons using different kinds of host‐guest interactions based on their electronic characteristics.

Abstract The fabrication of optoelectronic devices using low‐cost inkjet printing techniques is a topic of great interest to the scientific and industrial community and represents a step toward the full deployment of solution‐processable organic light emitting diodes (OLEDs), particularly for commercial lighting and signaling applications. Herein, the inkjet printing of tBuCzDBA (9,10‐bis(4‐(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)−2,6‐dimethylphenyl)−9,10‐diboraanthracene) is reported, a high‐performing thermally activated delayed fluorescence (TADF) emitter for OLEDs. Optimizing the surface tension values of the ink formulations and the associated wetting behavior are crucial parameters for achieving a uniform and homogeneous printed thin film. In particular, it is observed that using a proper mixture of solvents with different surface tensions, it is possible to generate Marangoni flows inside the drop, which triggers a very fast drying process, ensuring optimized morphological and optical properties in the inkjet printed tBuCzDBA‐based film. OLEDs exploiting this film as an emissive layer are then fabricated, achieving a maximum luminance of 32 000 cd m−2, a current efficiency of 27.5 cd A−1, and an external quantum efficiencyof 10%. To the best of the knowledge, this is the highest efficiency reported to date for self‐hosted TADF inkjet‐printed OLEDs.

Abstract A crystalline host matrix (CHM) with embedded nanoaggregates (NA) is a powerful strategy to develop high‐performance crystalline OLEDs that can combine the advantages of both crystalline and high‐exciton‐utilization‐efficiency light emitting materials. Here a CHM‐NA structure blue‐emission crystalline OLED is developed, which employs a thermally activated delayed fluorescence (TADF) material. The CHM‐TADFNA OLED is proved to efficiently manage exciton distribution by engineering nanoaggregates. The device exhibits a remarkable EQE up to 10.4% and achieves the characteristics of rapid turn‐on, and fast ramping of luminance and current density, resulting in an enhanced photon output and a lower series‐resistance Joule‐heat loss ratio, indicating a competitive pathway to future blue‐emission OLEDs.

Featured Application: A basic framework for further large-area OLEDs via printed electronics. The effects of the solvent used for the active layer materials of an OLED based on TADF emitters play a fundamental role in solution-deposited devices. This work focuses on the effects on the performance of different solvents employed to fabricate a very simple two-organic-layer OLED based on a green TADF emitter, under the concept of host: guest matrix. From the different results of the main figures of merit, it was possible to conclude that the OLED that used toluene as a solvent for the active layer reached a maximum EQE of 14%, almost the maximum already obtained for this emitter in more complex device structures. With the analysis of the charge-transport processes, it was possible to establish an explanatory model for the obtained results. Through impedance spectroscopy, additional characterization of the nature of charge-transport processes was carried out. With these results, it was possible to correlate the relaxation times, with the electrical properties of the active layer, and make inferences about the interaction between the electrical charges and the defect levels, opening new possibilities for further development in printed OLEDs. [ABSTRACT FROM AUTHOR]

Realizing high photoluminescence quantum yield (PLQY) in the near‐infrared (NIR) region is challenging and valuable for luminescent material, especially for thermally activated delay fluorescence (TADF) material. In this work, we report two achiral cyclic trinuclear Au(I) complexes, Au3(4‐Clpyrazolate)3 and Au3(4‐Brpyrazolate)3 (denoted as Cl−Au and Br−Au), obtained through the reaction of 4‐chloro‐1H‐pyrazole and 4‐bromo‐1H‐pyrazole with Au(I) salts, respectively. Both Cl−Au and Br−Au exhibit TADF with high PLQY (>70 %) in the NIR I (700–900 nm) (λmax = 720 nm) region, exceeding other NIR−TADF emitters in the solid state. Photophysical experiments and theoretical calculations confirmed the efficient NIR−TADF properties of Cl−Au and Br−Au were attributed to the small energy gap ΔE(S1‐T2) (S = singlet, T = triplet) and the large spin‐orbital coupling induced by ligand‐to‐metal‐metal charge transfer of molecular aggregations. In addition, both complexes crystallize in the achiral Pna21 space group (mm2 point group) and are circularly polarized light (CPL) active with maxima luminescent dissymmetry factor |glum| of 3.4 × 10−3 (Cl−Au) and 2.7 × 10−3 (Br−Au) for their crystalline powder samples, respectively. By using Cl−Au as the emitting ink, 3D‐printed luminescent logos are fabricated, which own anti‐counterfeiting functions due to its CPL behavior dependent on the crystallinity. [ABSTRACT FROM AUTHOR]

We report on organoboron complexes characterized by very small energy gaps (ΔEST) between their singlet and triplet states, which allow for highly efficient harvesting of triplet excitons into singlet states for working as thermally activated delayed fluorescence (TADF) devices. Energy gaps ranging between 0.01 and 0.06 eV with dihedral angles of ca. 90° were registered. The spin–orbit couplings between the lowest excited S1 and T1 states yielded reversed intersystem crossing rate constants (KRISC) of an average of 105 s−1. This setup accomplished radiative decay rates of ca. 106 s−1, indicating highly potent electroluminescent devices, and hence, being suitable for application as organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

A series of chiral mechanochromic copper(I) cAAC (cAAC=cyclic (alkyl)(amino)carbene) complexes with a variety of amide ligands have been studied with regard to their photophysical and chiroptical properties to elucidate structure‐property relationships for the design of efficient triplet exciton emitters exhibiting circularly polarized luminescence. Depending on the environment, which determines the excited state energies, either thermally activated delayed fluorescence (TADF) from 1/3LLCT states or phosphorescence from 3LLCT/LC states occurs. However, neither chiral moieties at the carbene nor at the carbazolate ligands provide detectable luminescence dissymmetries glum. An exception is [Cu(phenoxazinyl)(cAAC)], showing orange to deep red TADF with λmax=601–715 nm in solution, powders and in PMMA. In this case, the amide ligand can undergo distortions in the excited state. This design motif leads to the first linear, non‐aggregated CPL‐active copper(I) complex with glum of −3.4 ⋅ 10−3 combined with a high radiative rate constant of 6.7 ⋅ 105 s−1. [ABSTRACT FROM AUTHOR]

Utilizing purely organic materials with relatively highly emissive characteristics for designing organic light-emitting diodes (OLEDs) is fascinating since employing rare metals is unessential, hence, enormous research activities have been conducted in this field. Recently, additional efforts were devoted to designing special emitting materials demonstrating thermally activated delayed fluorescence (TADF). Molecular structures were ideally designed in a specific way using an electron-deficient molecule as an acceptor (A) and an electron-rich molecule as a donor (D) in order to minimize the overlapping between the highest occupied molecular orbital (HOMO) of the donor (D) and the lowest unoccupied molecular orbital (LUMO) of the acceptor (A). TADF requires a small band gap between the singlet excited and triplet excited states (ΔEST), usually less than (c.a 0.1 eV) of the luminescent material. This makes it possible to thermally harvest the excitons from the triplet excited state (T1) to the singlet excited state (S1) by a process known as reverse intersystem crossing (RISC) and then to harvest all the excitons for the fluorescence process. Thus, the design of the TADF molecular structure needs both an electron-rich segment as a donor and an electro-deficient segment as an acceptor. Up to the present, electron-deficient moieties (EDM) have been studied less than electron rich moieties (ERM) during the last few years. This review is highlighting the recent advances regarding the specific molecular designs of TADF emission materials for OLED applications, particularly, focusing on (dibenzothiophene-S,S-dioxide) as electron deficient molecule, which exhibits a strong electron-deficient unit and high ability of photo- and electroluminescence features. [ABSTRACT FROM AUTHOR]

Designing multi‐resonance (MR) emitters that can simultaneously achieve narrowband emission and suppressed intermolecular interactions is challenging for realizing high color purity and stable blue organic light‐emitting diodes (OLEDs). Herein, a sterically shielded yet extremely rigid emitter based on a triptycene‐fused B,N core (Tp‐DABNA) is proposed to address the issue. Tp‐DABNA exhibits intense deep blue emissions with a narrow full width at half maximum (FWHM) and a high horizontal transition dipole ratio, superior to the well‐known bulky emitter, t‐DABNA. The rigid MR skeleton of Tp‐DABNA suppresses structural relaxation in the excited state, with reduced contributions from the medium‐ and high‐frequency vibrational modes to spectral broadening. The hyperfluorescence (HF) film composed of a sensitizer and Tp‐DABNA shows reduced Dexter energy transfer compared to those of t‐DABNA and DABNA‐1. Notably, deep blue TADF‐OLEDs with the Tp‐DABNA emitter display higher external quantum efficiencies (EQEmax=24.8 %) and narrower FWHMs (≤26 nm) than t‐DABNA‐based OLEDs (EQEmax=19.8 %). The HF‐OLEDs based on the Tp‐DABNA emitter further demonstrate improved performance with an EQEmax of 28.7 % and mitigated efficiency roll‐offs. [ABSTRACT FROM AUTHOR]

Developing double boron‐based emitters with extremely narrow band spectrum and high efficiency in organic light‐emitting diodes (OLEDs) is crucial and challenging. Herein, we report two materials, NO‐DBMR and Cz‐DBMR, hinge on polycyclic heteraborin skeletons based on role‐play of the highest occupied molecular orbital (HOMO) energy levels. The NO‐DBMR contains an oxygen atom, whereas the Cz‐DBMR has a carbazole core in the double boron‐embedded ν‐DABNA structure. The synthesized materials resulted in an unsymmetrical pattern for NO‐DBMR and surprisingly a symmetrical pattern for Cz‐DBMR. Consequently, both materials showed extremely narrow full width at half maximum (FWHM) of 14 nm in hypsochromic (pure blue) and bathochromic (Bluish green) shifted emission without losing their high color fidelity. Furthermore, both materials show high photoluminescence quantum yield (PLQY) of over 82 %, and an extremely small singlet‐triplet energy gap (ΔEST) of 0.04 eV, resulting in high reverse intersystem crossing process (kRISC) of 105 s−1. Due to the efficient thermally activated delayed fluorescence (TADF) characteristics, the fabricated OLEDs based on these heteraborins manifested maximum external quantum efficiency (EQEmax) of 33.7 and 29.8 % for NO‐DBMR and Cz‐DBMR, respectively. This is the first work reported with this type of strategy for achieving an extremely narrow emission spectrum in hypsochromic and bathochromic shifted emissions with a similar molecular skeleton. [ABSTRACT FROM AUTHOR]

This review covers recent advances (from 2006 to date) in supramolecular systems based on fluorescent homooxacalixarenes, namely hexahomotrioxacalix[3]arenes, dihomooxacalix[4]arenes and tetrahomodioxacalix[4]arenes, focusing on fluorescence sensing using their intrinsic fluorescence (built-in mesitol-like groups) or the extrinsic fluorescence of organic fluorophores, either covalently linked to the calixarenes or forming supramolecular complexes with them. Sensing applications of ions, ion pairs and neutral molecules are discussed, as well as the potential measurement of temperature based on thermally activated delayed fluorescence.

The synthetic feasibility and excellent luminescence features of organic molecules attracted much attention and were eventually found useful in lighting applications. In this context, a solvent‐free organic liquid having attractive thermally activated delayed fluorescence features in bulk along with high processability has prime importance. Herein, we report a series of naphthalene monoimide‐based solvent‐free organic liquids exhibiting cyan to red thermally activated delayed fluorescence with luminescence quantum yields up to 80% and lifetimes between 10 to 45 μs. An effective approach explored energy transfer between liquid donors with various emitters exhibiting tunable emission colors, including white. The high processability of liquid emitters improved the compatibility with polylactic acid and was used for developing multicolor emissive objects using 3D printing. Our demonstration of the thermally activated delayed fluorescence liquid will be much appreciated as a processable alternate emissive material suitable for large‐area lighting, display, and related applications. [ABSTRACT FROM AUTHOR]

As a promising technology toward high‐efficiency organic light‐emitting diode (OLED), thermally activated sensitized fluorescence (TASF) has encountered major obstacles toward achieving sufficient operational lifetime when it comes to deep blue emission that is desirable for display applications. We have systematically investigated various factors affecting TASF OLED stability and successfully improved device lifetime by using a thermally activated delayed fluorescence (TADF) sensitizer with a fast reverse intersystem crossing rate (kRISC). [ABSTRACT FROM AUTHOR]

Two narrow emitting emitters were developed via a carbon/nitrogen (C/N) fusion strategy. The fusion‐induced rigid structures induced an MR effect similar to the boron frameworks. Both compounds offer narrow emission, very small Stocks shift, and high photoluminescence quantum yield. The fluorescence devices fabricated using m‐FLDID offer maximum efficiency (EQEmax) of above 5%, pure violet emission at 407 nm, and FWHM of 17 nm. Whereas the p‐ FLDID‐based thermally activated delayed fluorescence (TADF) devices showed EQEmax of above 25%, deep‐blue emission at 452 nm, and FWHM of 23 nm. [ABSTRACT FROM AUTHOR]

Organic light‐emitting diodes (OLEDs) are a widespread commercial display technology but they are still subject of ongoing research with the aim to expand their application ranges through stack and material design. Operational stability is one of the most important key properties that are steadily being improved. The long lifetimes of several thousands of hours of state‐of‐the‐art OLED structures at standard operating conditions demand for accelerated lifetime tests (ALTs) and the use of appropriate scaling laws for elevated temperatures and current densities. Here we present ALTs for a blue thermally activated delayed fluorescent (TADF) OLED and demonstrate the successful determination of the scaling parameters. Moreover, we study the microscopic degradation mechanisms using in‐situ electrical characterization methods. [ABSTRACT FROM AUTHOR]

In a hyperfluorescecne (HF) system, minimization of energy loss channel consisted of slow reverse intersystem crossing (RISC) and fast Dexter energy transfer (DET) is still challenging. Here, we report that such energy loss channels can minimize by utilizing quadrupolar donor‐acceptor‐donor (D‐A‐D) type TADF as sensitizer materials. We synthesized DBA‐DmICz and DBA‐DTMCz as D‐A‐D type TADF materials, which could suppress the DET process through fast RISC rate and shielded lowest unoccupied molecular orbital structure. The fabricated HF device with DBA‐DTMCz and v‐DABNA as a final dopant exhibited 43.9% of high maximum external quantum efficiency (EQEmax) with the CIE coordinates of (0.12, 0.16). [ABSTRACT FROM AUTHOR]

In order to investigate the joint influence of the conformation flexibility and the matching of the energies of the charge-transfer (CT) and the localized triplet excited (3LE) states on the thermally activated delayed fluorescence (TADF) in electron donor–acceptor molecules, a series of compact electron donor–acceptor dyads and a triad were prepared, with naphthalimide (NI) as electron acceptor and phenothiazine (PTZ) as electron donor. The NI and PTZ moieties are either directly connected at the 3-position of NI and the N-position of the PTZ moiety via a C–N single bond, or they are linked through a phenyl group. The tuning of the energy order of the CT and LE states is achieved by oxidation of the PTZ unit into the corresponding sulfoxide, whereas conformation restriction is imposed by introducing ortho-methyl substituents on the phenyl linker, so that the coupling magnitude between the CT and the 3LE states can be controlled. The singlet oxygen quantum yield (ΦΔ) of NI-PTZ is moderate in n-hexane (HEX, ΦΔ = 19%). TADF was observed for the dyads, the biexponential luminescence lifetime are 16.0 ns (99.9%)/14.4 μs (0.1%) for the dyad and 7.2 ns (99.6%)/2.0 μs (0.4%) for the triad. Triplet state was observed in the nanosecond transient absorption spectra with lifetimes in the 4–48 μs range. Computational investigations show that the orthogonal electron donor–acceptor molecular structure is beneficial for TADF. These calculations indicate small energetic difference between the 3LE and 3CT states, which are helpful for interpreting the ns-TA spectra and the origins of TADF in NI-PTZ, which is ultimately due to the small energetic difference between the 3LE and 3CT states. Conversely, NI-PTZ-O, which has a higher CT state and bears a much more stabilized 3LE state, does not show TADF.

A dimeric ZnII carbene complex featuring bridging and chelating benzene‐1,2‐dithiolate ligands is highly stable towards air and water. The donor‐Zn‐acceptor structure leads to visible light emission in the solid state, solution and polymer matrices with λmax between 577–657 nm and, for zinc(II) complexes, unusually high radiative rate constants for triplet exciton decay of up to kr=1.5×105 s−1 at room temperature. Variable temperature and DFT/MRCI studies show that a small energy gap between the 1/3LL/LMCT states of only 79 meV is responsible for efficient thermally activated delayed fluorescence (TADF). Time‐resolved luminescence and transient absorption studies confirm the occurrence of long‐lived, dominantly ligand‐to‐ligand charge transfer excited states in solution, allowing for application in Dexter energy transfer photocatalysis. [ABSTRACT FROM AUTHOR]

In this investigation, a systematic study on the design and development of corannulene‐based thermally activated delayed fluorescence (TADF) emitters using density functional theory methods is carried out. Benzene, benzopyrazine, difluoro‐benzopyrazine, benzene‐1,2‐dithiol, and tetrasulfone are introduced on corannulene bowl as electron‐withdrawing groups to alter the electron‐accepting property of corannulene. Three different donors, viz., carbazole, phenoxazine, and 5,10‐dihydrophenazine are substituted on the rim position of corannulene to alter the absorption properties. The relationship between chemical structure and TADF property is established by evaluating the dihedral angle between donor and acceptor units, spin–orbit coupling (SOC) values, the energy difference between singlet‐triplet excited states (ΔEST), and rates of reverse intersystem crossing (kRISC). The newly designed TADF emitters show absorption in the blue to near‐IR regions depending on the strength of the donor and acceptor moieties. Careful analysis of these properties delineates the relationship between SOC values and the nature of the excited states, which is crucial for achieving high kRISC. [ABSTRACT FROM AUTHOR]

Heavy atom effects and n-π* transitions have been frequently reported to enhance room-temperature organic phosphorescence efficiency but lead to shortage of phosphorescence lifetimes. Unlike these reported studies, we conceive the incorporation of advanced charge transfer (CT) technology to boost room-temperature organic afterglow efficiency and simultaneously maintain afterglow lifetimes. Here we design difluoroboron β-diketonate (BF2bdk) CT compounds with moderate singlet-triplet splitting energy (ΔEST) of around 0.4 eV, and relatively large spin-orbit coupling matrix elements (SOCME(S1-T1), 1–10 cm−1) to achieve efficient intersystem crossing (ISC) and moderate rates of reverse intersystem crossing (kRISC, 1–10 s−1). The advanced CT technology, which includes multiple electron-donating groups and orthogonal donor-acceptor arrangement, have been found to narrow ΔEST and enhance both ISC and RISC. Meanwhile, the organic matrices suppress nonradiative decay of BF2bdk's T1 states by their rigid microenvironment. Consequently, thermally activated delayed fluorescence (TADF)-type organic afterglow materials can be achieved with afterglow efficiency up to 83.0%, long lifetimes of 433 ms, excellent processablility, as well as advanced anti-counterfeiting and information encryption. Furthermore, with the aid of up-conversion materials and through radiative energy transfer, TADF-type afterglow materials with aqueous dispersity and near-infrared light- excitable property have been achieved, which paves the way for biomedical applications. [ABSTRACT FROM AUTHOR]

Solution-processed devices with thermally activated delayed fluorescence (TADF) compounds have gained great attention due to their low cost and high performance. Here, two solution-processable TADF emitters named ACCz-DPyM and POxCz-DPyM were synthesized by coupled 9,10-dihydro-9,9-dimethylacridine or phenoxazine modified carbazole as donor with di(pyridin-3-yl)methanone as acceptor. Both TADF compounds show same small ΔΕST of 0.04 eV and high PLQY of 66.2% and 58.2%. The devices fabricated by ACCz-DPyM and POxCz-DPyM as emitters show excellent performance as solution-processed with low turn-on voltage of 4.0 and 3.4 V, high luminance of 6209 and 3248 cd m−2 at 8 V, the maximum current efficiency of 9.9 and 15.9 cd A−1, the maximum external quantum efficiency of 6.6% and 6.5% and low efficiency roll-off. The solution-processed device based on ACCz-DPyM shows bluish-green emission. These results show that ACCz-DPyM and POxCz-DPyM are suitable for solution processing devices. [ABSTRACT FROM AUTHOR]

The synthesis, photophysical properties, and applications of highly fluorescent and phosphorescent palladium complexes are reviewed, covering the period 2018–2022. Despite the fact that the Pd atom appears closely related with an efficient quenching of the fluorescence of different molecules, different synthetic strategies have been recently optimized to achieve the preservation and even the amplification of the luminescent properties of several fluorophores after Pd incorporation. Beyond classical methodologies such as orthopalladation or the use of highly emissive ligands as porphyrins and related systems (for instance, biladiene), new concepts such as AIE (Aggregation Induced Emission) in metallacages or in coordination-driven supramolecular compounds (CDS) by restriction of intramolecular motions (RIM), or complexes showing TADF (Thermally Activated Delayed Fluorescence), are here described and analysed. Without pretending to be comprehensive, selected examples of applications in areas such as the fabrication of lighting devices, biological markers, photodynamic therapy, or oxygen sensing are also here reported. [ABSTRACT FROM AUTHOR]

There have been many advances in the development of thermally activated delayed fluorescence (TADF) materials for organic light emitting diode (OLED) applications in recent years. In particular, intramolecular exciplex systems have been highly studied and found to produce OLED devices of high external quantum efficiency (EQE) due to triplet harvesting via TADF. The proposed next generation of OLEDs uses hyperfluorescence to overcome the problem of broad emission associated with exciplexes. This process involves Förster resonance energy transfer (FRET) from the TADF host to a fluorescent dopant. In this work we revisited the photophysics of the TAPC:PBD exciplex (formed between the electron donor di-[4-(N , N -di- p -tolyl-amino)-phenyl]cyclohexane (TAPC) and the electron acceptor, 2-(4-biphenyl)-5-(4- tert -butylphenyl)-1,3,4-oxadiazole (PBD)) as a host capable of simultaneously performing triplet harvesting and work as a donor transferring energy to a bright fluorescent emitter. The aim is to investigate the interplay between energy transfer and intersystem crossing in this hyperfluorescence system. Contrarily to previous findings, films of the TAPC : PBD blend show relatively slow reverse intersystem crossing rate (RISC) and weak luminescence efficiency (PLQY). Despite this, when doped with the strong fluorescent emitter TTPA , the luminescence quantum yield is greatly improved due to the highly efficient energy transfer rate from TAPC : PBD to TTPA. The rapid FRET from the exciplex to the fluorescent emitter overcomes the non-radiative losses affecting the luminescence efficiency of the blend. This study shows that the hyperfluorescence mechanism not only allows colour purity in OLEDs to be optimised, but also facilitates suppressing major loss mechanisms affecting luminescence efficiency, thus creating conditions to maximizing EQE. [Display omitted] • A detailed photophysical study of the TAPC:PBD exciplex. • Exploration of the FRET mechanism to a fluorescent dopant TTPA. • Huge improvement of PLQY, from a poor triplet harvesting exciplex to a very bright hyperfluorescence system. [ABSTRACT FROM AUTHOR]

[Display omitted] Although OLEDs are widely employed nowadays for display technology devices, their application for room-lighting illumination remains a challenge due to the cost-effectiveness issues, mainly related to device fabrication. In this sense, the present study investigates the optimization of blue-emitting TADF (DMOC-DPS) and yellow-emitting TADF (TXO-TPA) compounds in solution-processed OLEDs to achieve efficient white light emission in a two-organic layer device. Four different host materials were studied, aiming to balance the charge mobility of holes and electrons. The host materials used include (in %wt.) a 1:1 mixture of mCP and DPEPO (HOST1), a 3:2 mixture of PVK and DPEPO (HOST2), a 3:2 mixture of PVK and mCP (HOST3), and a 3:2 mixture of PVK and butyl-PBD (HOST4). The experimental results obtained from the solution-processed OLEDs indicate that DMOC-DPS is predominantly a hole transport material, and hosts with predominantly n-type character, such as HOST1 and HOST4 , resulting in the most efficient white-OLEDs by the most balanced charge mobility. With structure optimization, WOLEDs achieved 6.43 % EQE with a brightness of 2621 cd/m2 (not integrated) and 6.06 % EQE with a brightness of 1986 cd/m2 for HOST4 and HOST1 , respectively. The emission characteristics were influenced by host materials characteristics, with blue and yellow emissions being fine-tuned to produce complementary colors. This study highlights the critical role of charge mobility balance in the emissive layer and demonstrates the potential of independently optimizing blue and yellow TADF components for high-performance WOLEDs suitable for indoor lighting applications. [Display omitted] • New approaches for solution-deposited WOLEDs based on complimentary color TADF emitters. • Electrical transport/recombination optimization in TADF host: guest WOLED deposited by solution-process techniques. • OLEDs simulation towards simplifyed/efficent device structure development. [ABSTRACT FROM AUTHOR]

Carbene-metal-amide (CMA) complexes based on cyclic(amino)(barrelene)carbene (CABC) ligands have been prepared for both Cu(I) and Au(I) metal centres. Synthetic protocols based on the conventional and microwave heating enabled ten-fold shorter reaction times and high yields of the CMA materials. Stabilization of the lowest unoccupied molecular orbital (LUMO) effects the electronic and photophysical properties. These materials benefit from short excited state lifetimes down to 0.9 μs and photoluminescence quantum yields up to 66 %. Nonradiative processes are revealed and associated with the rotational freedom of the aryl moiety in the CABC carbene ligand. Steady-state and time-resolved photoluminescence spectroscopy was used to estimate an activation energy barrier of 83 meV between singlet and triplet charge transfer (CT) excited states. Varied temperature photoluminescence confirms that 3CT photoluminescence remains even at 18 K, with no contribution from locally excited triplet states 3LE. Molecular design rules have been enhanced to propose bright thermally activated delayed fluorescence (TADF) CMA emitters. [Display omitted] • Microwave-assisted synthesis of carbene-metal-amide (CMA) materials in high yields. • Structure-property correlation to decipher the non-radiative process in CMA TADF materials. • Carbenes with high electrophilicity for future design of the red CMA TADF emitters. [ABSTRACT FROM AUTHOR]

In this study, we explore the impact of donor strength on the photophysical properties of novel trifluoromethyl quinoxaline derivatives, which incorporate various electron-donating moieties exhibiting distinct conformational characteristics. The triplet harvesting mechanisms within these quinoxaline systems are facilitated through thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP), both of which can be modulated by subtle structural alterations in the donor unit. The derivatives demonstrate varying photophysical properties, including pure RTP activity, dual activity (exhibiting both TADF and RTP), and pure TADF, contingent upon the nature of the electron-donating moieties employed. Notably, the intersystem crossing (ISC) rates are significantly higher than the rates of radiative decay, leading to diminished fluorescence quantum yields (Φ DF) of the compounds in toluene solutions. However, embedding the TADF compounds within a rigid polystyrene (PS) matrix results in a remarkable enhancement of Φ DF due to significant reduction of nonradiative pathways related to intramolecular twisting. A considerable conformational disorder of the polymer doped films was observed resulting in non-exponential fluorescence decay and significant shifts of prompt and delayed fluorescence in time-resolved spectra. • Triplet harvesting in quinoxalines is controlled by structural changes. • Films with dibenzoazepine in PS show efficient PF and RTP without oxygen. • Phenothiazine gives mixed TADF/RTP, while acridine shows pure TADF. [ABSTRACT FROM AUTHOR]

[Display omitted] • Role of electron acceptor substitution such as −CF 3 and –CN in PXZOXD were studied. • Photophysical analysis of the acceptor strength increment in PXZOXD is securitized. • Molecular photophysical changes delved with DFT and TDDFT studies. • OLEDs fabricated with –CN added PXZOXD showed greater performances with low ΔE ST. Herein, we reported the effect of electron withdrawing units, such as trifluoromethyl (CF 3) and cyanide (CN), substitution on a thermally activated delayed fluorescent (TADF) molecule (10-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)-10 H -phenoxazine (PXZ-OXD)). The addition of electron withdrawing units has increased the acceptor strength and reduced the interaction between PXZ and OXD, thus reducing the gap between the singlet and triplet states (ΔE ST) of excitons. To understand the variation in the acceptor strength of PXZ-OXD as a function of its molecular structure and density of states, density functional theory (DFT) and time-dependent DFT (TDDFT) were conducted. Transition density matrix investigations revealed that the addition of −CF 3 and –CN to PXZ-OXD triggers CT excitons, while inducing lower ΔE ST values. Particularly, the lowest ΔE ST (0.05 eV) with a notable red shift in the emission spectrum was observed with 4′-CF 3 PXZOXD. The delayed component lifetime of PXZOXD is found to be reduced after the substitution of −CNwhm and −CF 3. Despite the weak charge transfer transitions, the substitution of conjugative –CN group is found to be beneficial in improving the HOMO-LUMO overlap with a moderate decrease in reverse intersystem crossing (K RISC), which attained enhancement in the photoluminescent quantum yield. Additionally, the substitution of the above electron withdrawing units on PXZ-OXD yielded a red shift in the electroluminescence spectrum. Furthermore, the external quantum efficiency (at 100 cd/m2, i.e., EQE 100) of the 4′-CNPXZOXD-based organic light-emitting diode is found to improve by 21.13 % against the PXZOXD (16.9 %). [ABSTRACT FROM AUTHOR]