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Molecular emitters that combined thermally activated delayed and circularly polarized fluorescence (CP‐TADF) is of paramount importance for the next generation of displays. While most efforts have thus far focused on covalent donor and acceptor CP‐TADF emitters, a novel strategy based on chiral exciplexes has recently emerged. In this context, we present the synthesis and chiroptical properties of four new CP‐TADF exciplexes, involving two distinct C2‐symmetric bicarbazole systems and two terpyridine‐based derivatives, which serve as the chiral donor and achiral acceptor units, respectively. These exciplexes exhibit CP‐luminescence, with intensity dependent on both the chiral donor and achiral constituents, resulting in emission dissymmetry factors reaching up to 10⁻2 in the thin‐film solid state. Additionally, small singlet‐triplet gaps (∆EST ≤ 0.1 eV) have been measured, leading to TADF characteristics with a photoluminescence quantum yield of 20% for the most efficient emitter, which is also successfully used in non‐optimized organic lightemitting diodes (OLEDs). Interestingly, these chiral exciplexes allow us to explore the impact of the locally‐excited (LE) state of the chiral donor on overall exciplex emission, particularly in relation to the intensity of polarized emission—potentially highlighting a key factor in the design of this type of bimolecular CP‐TADF emitter. [ABSTRACT FROM AUTHOR]

Luminescent polymer composites based on polystyrene and polycarbonate doped with boron difluoride curcuminoids containing various substituents in the phenyl ring have been synthesized. The effect of substituents, polymer matrix, and luminophore concentration on the spectral properties of the polymer composites has been studied. It has been found that the effect of the electron-donating force of luminophore substituents on the emission characteristics of the films is similar to the effect of solutions. The films doped with luminophores containing alkyl substituents (1a–5a) do not change their emission characteristics upon switching to another polymer matrix, while the 6a-doped composites are characterized by positive solvatochromism. A bathofluoric shift of luminescence with an increase in the luminophore concentration to 0.5% is observed for all the films. It has been found that the 6a-doped films exhibit delayed fluorescence. [ABSTRACT FROM AUTHOR]

Luminescent polymer composites based on polycarbonate and polystyrene doped with boron difluoride β-ketoiminates have been synthesized. The luminescence properties of 12 dyes with various substituents have been studied. The effect of the boron difluoride β-ketoiminate concentration on the spectral properties of the samples has been studied. It has been found that the studied dyes exhibit monomer luminescence even with a tenfold increase in the luminophore concentration (from 0.05 to 0.5%). It has been revealed that composites containing boron difluoride 3-amino-1-phenyl-2-buten-1-onate (1a) and boron difluoride 3-methylamino-1-phenyl-2-buten-1-onate (2a) dyes in polystyrene exhibit exciplex luminescence. [ABSTRACT FROM AUTHOR]

The control of excited states and related emissive properties of gold(III) complexes mainly depends on the modulation of intramolecular electronic interactions among gold(III) metal center, chelating ligands and/or peripheral groups. However, luminescent gold(III) systems based on intermolecular electronic interactions have never been explored. Here we report a series of proof-of-concept gold(III) exciplexes using a simple gold(III) complex, AuDPPy, as an electron acceptor. The emissive properties of gold(III) exciplexes can be regulated by combining AuDPPy with different donors. Inspiringly, these gold(III) exciplexes have donor-dependent emission mechanisms: dominant phosphorescence or dual radiative channels of thermally activated delayed fluorescence (TADF) and phosphorescence. Consequently, these gold(III) exciplexes deliver green-to-red electroluminescence with external quantum efficiencies (EQEs) of up to 10.1%. More importantly, using these gold(III) exciplexes to host multi-resonance TADF emitters results in narrowband yellow, orange, and deep-red electroluminescence with high EQEs of 23.5%, 24.4%, and 27.4%, respectively, competitive to the highest values for gold(III) OLEDs in similar color gamut. [ABSTRACT FROM AUTHOR]

The luminescent properties of p- and m-nitrodibenzoylmethanates of boron difluoride are studied by via quantum-chemical modeling in combination with stationary and time-resolved luminescence spectroscopy. The effect the position of the nitro group has on the luminescent properties of the complexes has been revealed. In the series of donor substituents (phenyl, naphthyl, p-methoxyphenyl), compounds with p‑methoxyphenyl have the highest yield of luminescence quanta. The nitro group in the p-position (in contrast to the m-position) greatly reduces the yield of luminescence quanta. The formation of exciplexes is observed in the solutions of complexes in benzene, increasing the yield of luminescence quanta and creating a strong bathochromic shift of the luminescence spectrum's maximum. [ABSTRACT FROM AUTHOR]

For the first time, the fact of excitation of stimulated emission of blue, green, and red in color in air was discovered when an air mixture was irradiated at atmospheric pressure with light in the visible wavelength range. This phenomenon is observed only under sufficiently intense irradiation inside the reactor with reflective walls and is presumably explained by the formation of O(1S)–N2, O2(A3Σ)–N2, and O2(1Δ)–O2(1Δ) exciplexes and their stimulated emission. Under the conditions described, laser generation of blue, green, and red colors was observed in the air. A mechanism for a chain photochemical reaction is proposed to explain the observed phenomena. [ABSTRACT FROM AUTHOR]

[Display omitted] • Exciplex compounds, theoretical calculations to unraveling the excited fluorescence mechanism. • Exciplexes: electronic structure toward OLED devices. • Crossing ratesd excited states from TD-DFT methodologies. • Electroluminescence in TADF dimers. Most emissive materials have become significant research findings for building organic light-emitting diode (OLED) devices. Prominent organic electronics reach applications such as displays, lighting, and photodynamic therapy, among others. Thus, the area of organic emitters has rapidly developed thanks to the synergy between theoretical and experimental works. Here, organic emitters are accurately studied, describing their electronic structure, including the electronic transitions, excited state energies, and coupling characteristics. Consequently, a tandem of methodologies, such as density functional theory (DFT) and time-dependent density functional theory (TDDFT), besides the MD-ReaxFF simulations, were employed. Therefore, we focus on exciplex emitters reported as donating-accepting to describe the photophysical process contained in such emitters, establishing electron hopping rates from the monomer and dimeric conformations and assessing the singlet and triplet states. The evaluations of electronic coupling and the reorganization energy (λ) enable the accurate computing of crossing hopping for dimer and free dyes, proposing a reliable scheme of charge transfer properties. These findings bear a novel strategy for studying OLED devices and pave the way for developing more environmentally friendly technologies. [ABSTRACT FROM AUTHOR]

Luminescent exciplexes based on a chiral electron donor and achiral acceptors are reported as a new approach to design circularly polarized (CP) and thermally activated delayed fluorescence (TADF) emitters. This strategy results in rather high CP luminescence (CPL) values with glum up to 7×10−3, one order of magnitude higher in comparison to the CPL signal recorded for the chiral donor alone (glum ∼7×10−4). This increase occurs concomitantly with a CPL sign inversion, as a result of the strong charge‐transfer emission character, as experimentally and theoretically rationalized by using a covalent chiral donor‐acceptor model. Interestingly, blue, green‐yellow and red chiral luminescent exciplexes can be obtained by modifying with the electron accepting character of the achiral unit while keeping the same chiral donor unit. These results bring new (inter)molecular guidelines to obtain simply and efficiently multi‐color CP‐TADF emitters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu(I) exciplexes are developed using several Cu(I) carbene-metal-amide (CMA) complexes as donors. • Donor-dependent TADF emissions from copper(I)-perturbed through-space charge transfer excited states. • Narrowband electroluminescence with high EQEs of up to 24.9%. Organo-copper(I) emitters are promising cost-effective candidates as triplet-harvesting dopants in organic light-emitting diodes (OLEDs). To date, the mainstream design of Cu(I) emitters depends on ligand engineering to modify intramolecular charge transfer and thus modulate the related optoelectronic properties. However, little is known on luminescent Cu(I) systems based on intermolecular charge transfer. For the first time, the proof-of-concept Cu(I) exciplexes were developed employing a triazine-containing molecule DMIC-TRZ as an acceptor and several Cu(I)-based carbene-metal-amide (CMA) complexes as donors. The formation of these exciplexes is strongly associated with d-orbital participation of Cu atom on the highest occupied molecular orbital of CMA complexes to match with the acceptor DMIC-TRZ. These Cu(I) exciplexes not only displayed donor-dependent emission colors spanning from sky blue to red but also exhibited distinct thermally activated delayed fluorescence (TADF) via copper(I)-perturbed through-space charge transfer (TSCT). The OLEDs adopting the Cu(I) exciplexes as emitters delivered good external quantum efficiency (EQE) of up to 10.9%. Furthermore, the use of these Cu(I) exciplexes as hosts for multi-resonance TADF emitters delivered narrowband electroluminescence with high EQEs of up to 24.9%, superior to the reference OLEDs based on the common host. [ABSTRACT FROM AUTHOR]

The thermally-activated-delayed-fluorescence (TADF) characteristics makes exciplexes being the hot subject in the organic light-emitting diode (OLED) research field. The theoretical limit for the efficiency of the conventional fluorescent OLEDs have been leaped by exploiting the triplet harvesting ability of exciplexes. Exciplexes are easily formed by blending electron donor molecules and electron acceptor molecules, which are generally hole transporting materials and electron transporting materials, respectively, resulting in easy access for employing exciplexes to OLEDs. We introduce the photo-physical characteristics of exciplexes derived from the charge-transfer characteristics and their application to OLEDs as emitters. Single exciplex-emitting OLEDs as well as exciplex emission-based white OLEDs are covered in this review.

Exciplex emitters have been extensively studied owing to their natural thermally activated delayed fluorescence characteristic, and many efforts have been made to improve their performance in organic light emitting diodes (OLEDs). In this work, the authors propose a novel strategy by introducing intermolecular hydrogen bond (HB) between electron‐donating and electron‐accepting constituting molecules (D and A) to suppress non‐radiative transition of exciplex emitters and thus improve their efficiencies and stabilities in the OLEDs. Accordingly, three exciplex emitters are constructed by using 1,3‐di(10H‐phenoxazin‐10‐yl)benzene (13PXZB) as donor and 4,6‐bis(3,5‐di(pyridin‐4‐yl)phenyl)‐2‐methylpyrimidine (B4PyMPM), 4,6‐bis(3,5‐di(pyridin‐3‐yl)phenyl)‐2‐methylpyrimidine (B3PyMPM), and 4,6‐bis(3,5‐di(pyridin‐2‐yl)phenyl)‐2‐methylpyrimidine (B2PyMPM) as acceptors. With the most intermolecular HBs, 13PXZB:B4PyMPM shows the highest photoluminescence quantum yield (69.6%) and the lowest rate constant of non‐radiative process of triplet excitons (3.4 × 105 S−1). And the OLED using 13PXZB:B4PyMPM as the emitter successfully exhibits a much higher external quantum efficiency of 14.6% than other contrastive devices. Moreover, the half lifetime of 13PXZB:B4PyMPM is 4.8 and 8.2 times higher than those of 13PXZB:B3PyMPM and 13PXZB:B2PyMPM in the devices. This work not only demonstrates that intermolecular HBs between D and A molecules can improve the performance of exciplex emitters, but also paves a new route to develop efficient and stable exciplex emitters. [ABSTRACT FROM AUTHOR]

Exciplexes formed between donors and acceptors have been widely explored but isolating them from each other and tuning the interaction between the donor and acceptor have remained challenges. Here, we report donor/acceptor (D/A) pairs created by electrostatic interaction between a carbazole‐based anionic donor and a 1,3,5‐triazine‐based cationic acceptor and the exciplex formed within the pair. In a diluted film, the D/A pair affords an isolated exciplex which shows thermally activated delayed fluorescence (TADF). By changing the anchoring position of the imidazolium cation in the cationic acceptor, interactions between the donor and acceptor can be changed. Compared to the conventional exciplex formed in a neat film, the isolated exciplex exhibits a substantially higher luminescence efficiency. The D/A pairs show intriguing mechanochromic luminescence and mechanical grinding‐induced/reinforced TADF in the solid state and promising performances as emitters in organic light‐emitting diodes. [ABSTRACT FROM AUTHOR]

Organic light emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) utilize molecular systems with a small energy splitting between singlet and triplet states. This can either be realized in intramolecular charge transfer states of molecules with near‐orthogonal donor and acceptor moieties or in intermolecular exciplex states formed between a suitable combination of individual donor and acceptor materials. Here, 4,4′‐(9H,9′H‐[3,3′‐bicarbazole]‐9,9′‐diyl)bis(3‐(trifluoromethyl) benzonitrile) (pCNBCzoCF3) is investigated, which shows intramolecular TADF but can also form exciplex states in combination with 4,4′,4′′‐tris[phenyl(m‐tolyl)amino]triphenylamine (m‐MTDATA). Orange emitting exciplex‐based OLEDs additionally generate a sky‐blue emission from the intramolecular emitter with an intensity that can be voltage‐controlled. Electroluminescence detected magnetic resonance (ELDMR) is applied to study the thermally activated spin‐dependent triplet to singlet up‐conversion in operating devices. Thereby, intermediate excited states involved in OLED operation can be investigated and the corresponding activation energy for both, intra‐ and intermolecular based TADF can be derived. Furthermore, a lower estimate is given for the extent of the triplet wavefunction to be ≥ 1.2 nm. Photoluminescence detected magnetic resonance (PLDMR) reveals the population of molecular triplets in optically excited thin films. Overall, the findings allow to draw a comprehensive picture of the spin‐dependent emission from intra‐ and intermolecular TADF OLEDs. [ABSTRACT FROM AUTHOR]

Electron–hole pairs at the interface between electron‐donating and electron‐accepting molecules form charge‐transfer excitons (CTEs) via Coulomb attraction. Generally, the attraction energy of the CTE is weaker than that of the Frenkel exciton because of spatial separation of the charge pair; thus, the binding of the CTE is expected to be sensitive to an electric field. Here, the shielding of the binding energy of the CTEs by an internal electric field induced by spontaneous orientation polarization (SOP) of the solid‐state donor–acceptor blend film is reported. When the blend film forms a large SOP, the photogenerated CTEs spontaneously dissociate without an external electric field, resulting in carrier diffusion and carrier lifetimes that are in the milliseconds or longer. In the absence of a large SOP, the CTEs preferentially form exciplexes that quickly release their energy as light rather than dissociation. Hence, the control of SOP in the donor–acceptor blend films can provide new insights into exciton binding and facilitate the development of tailored high‐performance organic semiconductor devices. [ABSTRACT FROM AUTHOR]

With the inherent organic–metal system property, phosphorescent organic light‐emitting diodes (PhOLEDs) are capable of exhibiting high performance. However, the existence of unintended triplet–triplet annihilation (TTA), which is mainly originated from high triplet exciton density leading to inferior device performance, is a current predicament. For mitigating the TTA in devices, reported herein is an effective host system with the role of precisely controlling the triplet excitons via the multichannel processes, in which a bipolar host material, a hole‐transporting material, and an electron‐transporting material are mixed to manage the triplet exciton transfer. The mixed‐host with so‐called "triplet excitons harvesting" strategy exhibits two concomitant reverse intersystem crossing (RISC) processes that simultaneously occur in the bipolar host material:electron‐transporting material and the host‐transporting material:electron‐transporting material exciplexes, respectively. Highly efficient green and red PhOLEDs are demonstrated by these multichannel processes, in which phosphorescent emitters bis(2‐phenylpyridine) (acetylacetonate) iridium(III) (Ir(ppy)2(acac)) and bis(2‐methyldibenzo[f,h]‐quinoxaline) (acetylacetonate) iridium(III) (Ir(MDQ)2(acac)) are doped into the mixed‐host, respectively. The green and red PhOLEDs realize nearly 30% of maximum external quantum efficiencies of 29.4% and 29.2%, respectively, and also maintain 29.1% and 28.3% at 1000 cd m−2. These excellent efficiencies and low roll‐offs confirm that the concomitant RISC processes effectively manage and utilize triplet excitons. [ABSTRACT FROM AUTHOR]

Excimers and exciplexes are defined as assemblies of atoms or molecules A/A′ where interatomic/intermolecular bonding appears only in excited states such as [A2]* (for excimers) and [AA′]* (for exciplexes). Their formation has become widely known because of their role in gas‐phase laser technologies, but their significance in general chemistry terms has been given little attention. Recent investigations in gold chemistry have opened up a new field of excimer and exciplex chemistry that relies largely on the preorganization of gold(I) compounds (electronic configuration AuI(5d10)) through aurophilic contacts. In the corresponding excimers, a new type of Au⋅⋅⋅Au bonding arises, with bond energies and lengths approaching those of ground‐state Au−Au bonds between metal atoms in the Au0(5d106s1) and AuII(5d9) configurations. Excimer formation gives rise to a broad range of photophysical effects, for which some of the relaxation dynamics have recently been clarified. Excimers have also been shown to play an important role in photoredox binuclear gold catalysis. [ABSTRACT FROM AUTHOR]

Near‐infrared exciplex can weaken molecular design difficulties, and has the advantage of easy bathochromic‐shift spectra via selecting the suitable electron donors and acceptors. In this contribution, exciplex is applied to fabricate near‐infrared (NIR) organic light‐emitting diodes (OLEDs) incorporating a synthesized fluorescent material 3‐([1,1″:3′,1″‐terphenyl]‐5′‐yl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC‐tPh) and a commercially available material 4,4′,4″‐tris(carbazol‐9‐yl)triphenylamine (TCTA). The device having a mixed TCTA:APDC‐tPh as an emitting layer shows a 730 nm NIR emission with a maximum external quantum efficiency (EQE) of about 0.1%, while the device having 2‐[4‐(diphenylamino)phenyl]‐10,10‐dioxide‐9H‐thioxanthen‐9‐one (TXO‐TPA):APDC‐tPh as the emitting layer exhibits an emission peak of 704 nm with a maximum EQE of 1.27%. These results prove the feasibility of fabricating the efficient exciplex‐based NIR OLEDs. [ABSTRACT FROM AUTHOR]

Exciplex or excited complex emission is an excited state process, arising from considerable charge transfer of an excited energy donor to an acceptor, which can be identified by the occurrence of a redshifted emission band that is absent in the individual constituents. Particularly interesting are exciplexes that are formed by intramolecular excited state interaction, which are inherently concentration independent. Based upon our previous experience in the Ugi-4CR syntheses of donor-acceptor conjugates capable of photo-induced intramolecular electron transfer (PIET), that is, generation of light-induced charge separation, we now disclose the diversity-oriented approach on unimolecular exciplex emitters and their reference systems by Ugi-4CR. The photophysics is studied by absorption and emission spectroscopy and accompanied by density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations.

The thermally-activated-delayed-fluorescence (TADF) characteristics makes exciplexes being the hot subject in the organic light-emitting diode (OLED) research field. The theoretical limit for the efficiency of the conventional fluorescent OLEDs have been leaped by exploiting the triplet harvesting ability of exciplexes. Exciplexes are easily formed by blending electron donor molecules and electron acceptor molecules, which are generally hole transporting materials and electron transporting materials, respectively, resulting in easy access for employing exciplexes to OLEDs. We introduce the photo-physical characteristics of exciplexes derived from the charge-transfer characteristics and their application to OLEDs as emitters. Single exciplex-emitting OLEDs as well as exciplex emission-based white OLEDs are covered in this review. [ABSTRACT FROM AUTHOR]

Deep‐red to near‐infrared (NIR) OLEDs, which yield emission peak wavelengths beyond λ=660 nm, are applicable as unique light sources in plant growth or health monitoring systems. Compared with other visible‐spectrum OLEDs, however, research in the field of deep‐red OLEDs is not as advanced. In this work, three new types of dibenzofuran‐based host materials are developed as n‐type exciplex host partners. Combining these with the deep‐red iridium complex bis(2,3‐diphenylquinoxaline)iridium(dipivaloylmethane) ([(DPQ)2Ir(dpm)]) and N,N′‐di(naphalene‐1‐yl)‐N,N′‐diphenylbenzidine (α‐NPD) as a p‐type exciplex host partner, a highly efficient deep‐red OLED can be realized with a maximum external quantum efficiency (ηext,max) of over 16 % with Comission Internationale de l′Éclairge (CIE) coordinates of (0.71, 0.28). In addition, the effect of the doping concentration and the p/n ratio of the exciplex host on the efficiency and the lifetime of the OLEDs are investigated. Consequently, the optimized device exhibits a ηext,max of over 15 % and a six‐time longer lifetime operating at high brightness of 100 cd m−2 compared with other state‐of‐the‐art deep‐red OLEDs. [ABSTRACT FROM AUTHOR]

The complex photokinetics of donor-acceptor-donor triads with varying flexible spacer lengths (n = 4-10 carbon atoms) are investigated in liquid and solid solution, as well as in crystals, by steady-state and transient fluorescence spectroscopy combined with computational studies. For the short spacer (n = 4) in a liquid solution, dynamic charge-transfer (CT) state formation with subsequent, efficient exciplex emission is observed, effectively competing with quenching through electron transfer (eT) via a radical ion pair. In a solid solution, a fluorescent CT static complex is formed upon freezing for all spacer lengths. This allows the observations of a former seminal report on stimuli-responsive high-contrast fluorescence on/off switching in films of the triads to be reassigned (Adv. Mater. 2012, 24, 5487), now providing a holistic picture on varying spacer length. In fact, external stimuli of the film by modulating the geometry of the CT complex, which results in on/off fluorescence switching (for n > 4) or in a change of the emission color (n = 4). The work thus demonstrates how in-depth analysis of complex photophysics can be put to practical use in materials science., (© 2023 Wiley-VCH GmbH.)

Abstract: Regarding lighting application, the main challenges for white organic light‐emitting diodes (WOLEDs) include the complicated structure, the high cost, and the low repeatability, which are attributed to the stringent requirement on the exciton allocation and utilization in multiradiation systems. Herein, an effective “full‐radiation white emission (FRWE)” strategy for the dynamic exciton allocation is successfully demonstrated by the first dual‐emissive blue‐emitting exciplex mCP:pTPOTZ. On the basis of an ultrasimple trilayer structure and bimaterial/trimaterial systems, its blue, yellow, and white devices realize state‐of‐the‐art performances. Especially, mCP:pTPOTZ supports its WOLEDs with ultralow driving voltages and extremely high efficiencies beyond 90 lm−1 and 24%, accompanied by a negligible roll‐off less than 10% at 1000 cd m−2. This work not only establishes a feasible method to construct dual‐emissive exciplex systems through the modulation of the donor–acceptor packing modes, but also demonstrates the superiority of FRWE strategy in 100% exciton harvesting and quenching suppression, which makes simple but high‐performance WOLED‐based lighting sources become a reality. [ABSTRACT FROM AUTHOR]

Abstract: Understanding excited‐state dynamics is critical for improving the photoluminescence (PL) efficiency of exciplexes. A series of exciplexes based on conventional hole‐transporting materials as donor and newly developed phenylpyridinato boron derivatives as acceptor were investigated. High PL efficiencies were achieved in only some combinations, and a large difference in performance among combinations provided insight into nonradiative processes in exciplex systems. Furthermore, the triplet local excited states (3LE) of each donor and acceptor were found play an important role in triplet exciplex harvesting. Significant contributions from triplets were clearly observed when the charge‐transfer excited states (1CT and 3CT) and 3LE were ideally aligned. We also demonstrated fine control of relative energy alignment via the concentration to improve the PL efficiency. [ABSTRACT FROM AUTHOR]

The precise stereocontrol of photocycloaddition reactions is still a significant challenge owing to their mechanistic complexity and the involvement of highly reactive and short-lived intermediates. Attempts have hitherto been made through structural modifications, mostly by introducing steric conflicts, to increase the difference between the enthalpic barriers. Herein, we show that entropy plays a crucial role in influencing the diastereoselectivity of a Paternò–Büchi reaction. Remote meta alkylation of the donor caused nominal changes in its photophysical properties as well as those of the exciplexes derived thereof. Nevertheless, the diastereomeric excess of the oxetane product was greatly improved by about 40%. This enhancement, which is not accompanied by any significant changes in the photophysical properties, is difficult to rationalize by conventional enthalpic control concepts based on repulsive steric and/or attractive intermolecular interactions as well as electronic perturbations. Differential activation parameters and compensatory enthalpy–entropy relationships revealed that the diastereoselectivity enhancement is not simply enthalpic but also entropic in origin. [ABSTRACT FROM AUTHOR]

In this paper, multiple-exciplexed white organic light-emitting diodes (WOLEDs) with blue and yellow - green emitting layers (EMLs) to improve charge balance and efficiency roll-off through exciton confinement are investigated. Several types of WOLEDs are fabricated a number of including exciplex generated by only host materials without fluorescent or phosphorescent dopant. Moreover, various multiple exciplex can control electrical behavior of holes and electrons in whole EML. The performance improvement by the insertion of multi-EMLs is realized throughout enhancement of exciton confinement and the reduced exciton quenching in EML. Efficiency roll-off was 40% improved comparing to WOLED without multi-EMLs and also color rendering index was achieved higher than 70 at 1000 cd m-2 in WOLED with multi-EMLs. [ABSTRACT FROM AUTHOR]

Aromatic difluoroboronated β-diketone ( BF2DK) derivatives are a widely known class of luminescent organic materials that exhibit high photoluminescent quantum efficiency and unique aggregation-dependent fluorescence behavior. However, there have been only a few reports on their use in solid-state electronic devices, such as organic light-emitting devices (OLEDs). Herein, we investigated the solid-state properties and OLED performance of a series of π-extended BF2DK derivatives that have previously been shown to exhibit intense fluorescence in the solution state. The BF2DK derivatives formed exciplexes with a carbazole derivative and exhibited thermally activated delayed fluorescence (TADF) behavior to give orange electroluminescence with a peak external quantum efficiency of 10 % that apparently exceeds the theoretical efficiency limit of conventional fluorescent OLEDs (7.5 %), assuming a light out-coupling factor of 30 %. [ABSTRACT FROM AUTHOR]

The applicabilities of various CIS- and TDDFT-based procedures to the calculation of the fluorescence spectra of DBMBF2 exciplexes with aromatic hydrocarbons are analyzed. It is shown that a reasonable agreement between the calculated and experimental fluorescence spectra is obtained when a combined procedure is used. In this combined procedure, the geometries of the exciplexes are optimized beforehand using the CIS method with an empirical dispersion correction, while the exciplex transition energies are calculated at the optimized geometries using the CIS(D) method or the TDDFT approach with double-hybrid B2PLYP and mPW2PLYP functionals. [ABSTRACT FROM AUTHOR]

Electronic absorption and luminescence spectra of four new compounds of divinyldiphenyl and divinylphenanthrene derivatives are investigated experimentally in tetrahydrofuran solutions and thin films obtained by thermal vacuum deposition and by spin coating of these substances embedded into polyvinylcarbazole matrix. Molecular geometry optimizations and electronic spectra have been calculated in the framework of XMC-QDPT2/6-31G (d, p) and TDDFT/B3LYP/6-31G (d, p) levels of theory. We have fabricated and studied OLED devices with the structure ITO/PEDOT:PSS/NPD/L/Ca/Al and ITO/PEDOT:PSS/PVK + L/Ca, where L is the luminophore. It is demonstrated that the photo-and electroluminescence spectra of divinyldiphenyl are not identical and undergo strong changes depending on the method of sample preparation. [ABSTRACT FROM AUTHOR]

In the title compound, C23H16O2S, the thiophene group is rotationally disordered into two fractions almost parallel to each other, with occupation factors of 0.523 (7) and 0.477 (7), and subtending dihedral angles of 10.5 (5) and 9.3 (5)°, respectively, to the thiophene group. The molecules are held together by weak C—H...O and C—H...π hydrogen bonds, producing a laminar arrangement, which are further connected in a perpendicular fashion by S...π contacts [S...centroid = 3.539 (8) and 3.497 (8) Å]. In spite of the presence of the entended pyrene group, the structure does not present any parallel π–π stacking interactions. The structure was refined as an inversion twin.

A new family of thermally activated delayed fluorescence (TADF) emitters based on U-shaped D-A-D architecture with a novel accepting unit has been developed. All investigated compounds have small singlet-triplet energy splitting (Δ EST) ranging from 0.02 to 0.20 eV and showed efficient TADF properties. The lowest triplet state of the acceptor unit plays the key role in the TADF mechanism. OLEDs fabricated with these TADF emitters achieved excellent efficiencies up to 16 % external quantum efficiency (EQE). [ABSTRACT FROM AUTHOR]

The unprecedented dependence of final charge separation efficiency as a function of donor-acceptor interaction in covalently-linked molecules with a rectilinear rigid oligo-p-xylene bridge has been observed. Optimization of the donor-acceptor electronic coupling remarkably inhibits the undesirable rapid decay of the singlet charge-separated state to the ground state, yielding the final long-lived, triplet chargeseparated state with circa 100% efficiency. This finding is extremely useful for the rational design of artificial photosynthesis and organic photovoltaic cells toward efficient solar energy conversion. [ABSTRACT FROM AUTHOR]

A new strategy is reported for multicolor fluorescence writing on thin solid films with mechanical forces. This concept is illustrated by the use of a green-fluorescent pentiptycene derivative 1, which forms variably colored fluorescent exciplexes: a change from yellow to red was observed with anilines, and fluorescence quenching (a change to black) occurred in the presence of benzoquinone. Mechanical forces, such as grinding and shearing, induced a crystalline-to-amorphous phase transition in both the pristine and guest-adsorbed solids that led to a change in the fluorescence color (mechanofluorochromism) and a memory of the resulting color. Fluorescence drawings of five or more colors were created on glass or paper and could be readily erased by exposure to air and dichloromethane fumes. The structural and mechanistic aspects of the observations are also discussed. [ABSTRACT FROM AUTHOR]

Helium nanodroplets have emerged as a test bed for the study of isolated quantum liquids and as an ideal matrix for trapping atoms and molecules in a weakly interacting, cryogenic environment. Their high transparency at visible and infrared wavelengths facilitates the study of dissolved species with traditional spectroscopy techniques. At photon energies above ~21 eV, however, the droplets themselves begin to absorb to form complex excited states that have proven a challenge for both experiment and theory. A variety of frequency- and time-domain methods have been used to characterise electronically excited droplet states and their relaxation channels. This review focuses on a recent series of time-domain experimental studies that have revealed several phenomena such as interband relaxation dynamics within the droplet environment, and provided deeper insight into previously detected relaxation channels, including the ejection of Rydberg atoms (He*) and molecules (), the dynamics of highly excited droplet states, and photoassociation to produce strongly-bound excimer species (such as). A brief outline of correspondingab initioefforts for the theoretical description of electronically excited He droplet states and their relaxation dynamics will also be given. [ABSTRACT FROM PUBLISHER]

Highly fluorescent excited-state charge-transfer complexes (exciplexes) formed at the interfacial region between a polymeric donor matrix, here, poly( N-vinylcarbazole), and embedded nanostructured acceptors are characterized for their photophysical properties. Exciplex-to-exciton emission switching is observed after solvent vapor annealing (SVA) due to the size evolution of the nanostructures beyond the exciton diffusion length. Color-tunable exiplex emission (sky blue, green, and orange) is demonstrated for three different nanostructured acceptors with the same HOMO-LUMO gap (i.e., the same blue excitonic emission) but with different electron affinity. White-emitting poly( N-vinylcarbazole) film is also fabricated, simply by incorporating mixed supramolecular acceptors, which provide independent exciplex emissions. This study presents important insights into the excited-state intermolecular interaction at the well-defined nanoscale interface and suggests an efficient way to obtain multicolored exciplex emissions. [ABSTRACT FROM AUTHOR]

Phosphorescent organic light-emitting diodes (OLEDs) with ultimate efficiency in terms of the external quantum efficiency (EQE), driving voltage, and efficiency roll-off are reported, making use of an exciplex-forming co-host. This exciplex-forming co-host system enables efficient singlet and triplet energy transfers from the host exciplex to the phosphorescent dopant because the singlet and triplet energies of the exciplex are almost identical. In addition, the system has low probability of direct trapping of charges at the dopant molecules and no charge-injection barrier from the charge-transport layers to the emitting layer. By combining all these factors, the OLEDs achieve a low turn-on voltage of 2.4 V, a very high EQE of 29.1% and a very high power efficiency of 124 lm W−1. In addition, the OLEDs achieve an extremely low efficiency roll-off. The EQE of the optimized OLED is maintained at more than 27.8%, up to 10 000 cd m−2. [ABSTRACT FROM AUTHOR]

A feasibility of formation of donor-acceptor charge-transfer (CT) complexes between melanin and 2,4,7-trinitrofluorenone (TNF) being good electron acceptor has been studied in solutions by means of the absorption and photoluminescence (PL) spectra. The model of electronic transitions in a melanin-TNF composite solution has been proposed. [ABSTRACT FROM PUBLISHER]

Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in solution and in doped hosts. A series of spectroscopic methods (luminescence, UV-reflectance, IR, and Raman) as well as theoretical calculations have confirmed the existence of excimers and exciplexes. This leads to the tunability of these nano systems over a wide wavelength interval. The population of these nanoclusters varies with temperature and external laser irradiation, which explains the thermochromism and optical memory. DFT calculations indicate an MLCT transition for each nanocluster and the emission energy decreases with increasing cluster size. This is in agreement with the relatively long life-time for the emission peaks and the multiple emission peaks dependence upon cluster concentration. [ABSTRACT FROM AUTHOR]

Abstract: The [Pt2(H2P2O5)4]4− ions in the ground and excited states and the excited-state complexes M-[Pt2(H2P2O5)4]3− and M2-[Pt2(H2P2O5)4]2− (M=Ag, Tl) were studied in solution with various density functional theory (DFT) functionals from Gaussian 09 and Amsterdam Density Functional (ADF) programs. Calculated results were compared with ultrafast X-ray solution scattering data. Time dependent DFT (TD-DFT) calculations with the B3PW91 functional and unrestricted open shell calculations with the mPBE functional produce good agreement with the experimental results. Compared to gas phase calculations, the surrounding solvent is found to play an important role to shorten the Pt–Pt and M–Pt (M=Ag, Tl) bond lengths, lowering the molecular orbital energies and influences the molecular orbital transitions upon excitation, which stabilizes the excited transient molecules in solution. [Copyright &y& Elsevier]

Abstract: A new approach to determination of the recombination rate of radical ion pairs in moderately polar solvents is presented. It is based on an investigation of transient photocurrents caused by dissociation of exciplexes generated in photoinduced electron transfer reactions. It has been shown that the recombination rate of geminate ion pairs can be found from the photocurrent rise time. We have applied such an approach to transient photocurrents observed by Hirata et al. [Y. Hirata, Y. Kanda, N. Mataga, J. Phys. Chem. 87 (1983) 1659] for the pyrene/dicyanobenzene system in solvents of moderate polarity. The increase of the obtained recombination rate of photogenerated ions with increasing polarity of solvent testifies that ions recombine mainly by the backward electron transfer from the dicyanobenzene anions to solvent-separated cations of pyrene. [Copyright &y& Elsevier]

[Display omitted] • Four bipolar molecules were designed and synthesized for accessing exciplex and electroplex host systems. • Highly efficient green PhOLED with EQE max of 29.9% was achieved. • Extremely small efficiency roll-offs (1.3% at 1,000 cd m−2; 5.4% at 5,000 cd m−2) were obtained. Host materials are of great significance to achieve high-performance host–guest organic light-emitting diodes (OLEDs) through restraining the exciton annihilation in the emissive layer. Herein, four bipolar molecules bearing benzothienocarbazole (BTCz)/benzothienocarboline (BTCb) and benzimidazole (Bi) moieties were designed and synthesized. Using them as hosts, green phosphorescent OLEDs (PhOLEDs) with maximum current efficiency (CE max) of 90.8 cd A−1, power efficiency (PE max) of 76.5 lm W−1, and external quantum efficiency (EQE max) of 27.9% were obtained. More importantly, it was found that these four molecules could be used as electron-donating materials to interact with electron-accepting triazine derivatives to form electroplexes. Employing these electroplexes as hosts, highly efficient green PhOLEDs with CE max of 104.4 cd A−1, PE max of 85.1 lm W−1, EQE max of 29.9%, and extremely small efficiency roll-offs (EQE = 29.5%, 1.3% roll-off at 1,000 cd m−2; EQE = 28.3%, 5.4% roll-off at 5,000 cd m−2) were achieved. The excellent device performances fully exhibit the promising potential of electroplexes as hosts for high-performing OLEDs. [ABSTRACT FROM AUTHOR]