A series of gold‐centered carbene‐metal‐amide (CMA) complexes are synthesized with the carbazole donor ligand modified by substitution with nitrogen atoms in varying positions. The luminescence of new aza‐CMA complexes shows a significant blueshift depending on the position of the N atom, to provide bright blue‐green (500 nm), sky‐blue (478 nm), blue (450 nm) and deep‐blue (419 nm) light‐emitters. The impact of the electron‐withdrawing aza‐group on the nature of the luminescence and the excited state energies of the locally excited (LE) or charge transfer (CT) states have been interpreted with the help of transient absorption, in‐depth photoluminescence experiments and theoretical calculations. By considering the orbital characters of the lowest CT and LE states, we develop a new concept for simultaneous energy tuning for both of these states with a single aza‐substitution, allowing for fast and blue CT emission. This concept allows the interference of 3 LE phosphorescence to be avoided at room temperature. The approach is extended to two N substitutions at the optimal location in the 3‐ and 6‐positions of the carbazole skeleton. These results suggest a practical molecular design towards the development of bright and deep‐blue emitting CMA materials to tackle the stability problem of energy‐efficient deep‐blue OLEDs.

Carbene-metal-amides (CMAs) are an emerging class of photoemitters based on a linear donor-linker-acceptor arrangement. They exhibit high flexibility about the carbene-metal and metal-amide bonds, leading to a conformational freedom which has a strong influence on their photophysical properties. Herein we report CMA complexes with (1) nearly coplanar, (2) twisted, (3) tilted, and (4) tilt-twisted orientations between donor and acceptor ligands and illustrate the influence of preferred ground-state conformations on both the luminescence quantum yields and excited-state lifetimes. The performance is found to be optimum for structures with partially twisted and/or tilted conformations, resulting in radiative rates exceeding 1 × 106 s-1. Although the metal atoms make only small contributions to HOMOs and LUMOs, they provide sufficient spin-orbit coupling between the low-lying excited states to reduce the excited-state lifetimes down to 500 ns. At the same time, high photoluminescence quantum yields are maintained for a strongly tilted emitter in a host matrix. Proof-of-concept organic light-emitting diodes (OLEDs) based on these new emitter designs were fabricated, with a maximum external quantum efficiency (EQE) of 19.1% with low device roll-off efficiency. Transient electroluminescence studies indicate that molecular design concepts for new CMA emitters can be successfully translated into the OLED device.

Fluorescence in biological systems is usually associated with the presence of aromatic groups. Here, by employing a combined experimental and computational approach, we show that specific hydrogen bond networks can significantly affect fluorescence. In particular, we reveal that the single amino acid L-glutamine, by undergoing a chemical transformation leading to the formation of a short hydrogen bond, displays optical properties that are significantly enhanced compared with L-glutamine itself. Ab initio molecular dynamics simulations highlight that these short hydrogen bonds prevent the appearance of a conical intersection between the excited and the ground states and thereby significantly decrease nonradiative transition probabilities. Our findings open the door to the design of new photoactive materials with biophotonic applications.

The effect of the heavy metal atom on the photophysics of carbene-metal-amide (CMA) photoemitters is explored, where the metal bridge is either Au, Ag, or Cu. Spectroscopic investigations reveal the coupling mechanism responsible for communication between the singlet and triplet manifolds. The photophysical properties do not reflect expected trends based upon the heavy atom effect, as both direct coupling between charge-transfer states and spin-vibronic coupling via a ligand-centered triplet state are present. Direct coupling is weakest for CMA(Ag), increasing the importance of the spin-vibronic pathway and rendering its properties more sensitive to inter-state energy gaps than for the Au and Cu-bridged analogues. The measured activation energy correlates with the expected exchange energy of the charge-transfer state, which is also closely related to the length of the bonds joining the carbene and amide ligands, and decreases in the order CMA(Cu) > CMA(Au) > CMA(Ag). These findings reveal that reducing interference between charge-transfer and ligand-centers excited, and minimizing exchange energy, are required for developing efficient luminescent CMA complexes.

A wide‐gap host matrix is a major obstacle detrimentally influencing the performance of hyperfluorescent organic light‐emitting diodes since it substantially increases driving voltage. Moreover, these hyperfluorescent devices typically require at least three components in their emitting layer, which is unfavorable for mass production. To tackle the issue, hyperfluorescent organic light‐emitting diodes are reported based on a two‐component emissive system of carbene–metal–amide donors and conventional fluorescent acceptors. A significant reduction of the driving voltage versus three‐component hyperfluorescent devices at practical brightness (1000 cd m –2 ) is demonstrated, leading to a doubling of power conversion efficiency for some composites. From an analysis of thin‐film photophysics, it is shown that operational efficiency is limited by Dexter energy transfer between donors and acceptors, which may be reduced by tert ‐butyl steric substituents, providing new targets for molecular design. While reducing driving voltage, matrix‐free hyperfluorescent devices also achieve a maximum external quantum efficiency of 16.5%.

Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular CT excitonic states and associated small singlet-triplet energy; triplets can be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient ESR studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between LE and CT triplets. The observation of distinct triplet signals, unusual in transient ESR, suggests that multiple triplets mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between LE and CT triplets decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states.

Multiple donor–acceptor‐type carbazole–benzonitrile derivatives that exhibit thermally activated delayed fluorescence (TADF) are the state of the art in efficiency and stability in sky‐blue organic light‐emitting diodes. However, such a motif still suffers from low reverse intersystem crossing rates (kRISC) with emission peaks <470 nm. Here, a weak acceptor of cyanophenyl is adopted to replace the stronger cyano one to construct blue emitters with multiple donors and acceptors. Both linear donor–π–donor and acceptor–π–acceptor structures are observed to facilitate delocalized excited states for enhanced mixing between charge‐transfer and locally excited states. Consequently, a high kRISC of 2.36 × 106 s−1 with an emission peak of 456 nm and a maximum external quantum efficiency of 22.8% is achieved. When utilizing this material to sensitize a blue multiple‐resonance TADF emitter, the corresponding device simultaneously realizes a maximum external quantum efficiency of 32.5%, CIEy ≈ 0.12, a full width at half maximum of 29 nm, and a T80 (time to 80% of the initial luminance) of > 60 h at an initial luminance of 1000 cd m−2.

The excited state properties and intersystem crossing dynamics of a series of donor-bridge-acceptor carbene metal-amides based upon the coinage metals Cu, Ag, Au, are investigated using quantum dynamics simulations and supported by photophysical characterisation. The simulated intersystem rates are consistent with experimental observations making it possible to provide a detailed interpretation of the excited state dynamics which ultimately control their functional properties. It is demonstrated that for all complexes there is a competition between the direct intersystem crossing occurring between the 1CT and 3CT states and indirect pathways which couple to an intermediate locally excited ππ* triplet state (3LE) on either the donor or acceptor ligands. The energy of the 3LE states decreases as the size of the metal decreases meaning that the indirect pathway plays an increasingly important role for the lighter metals. Importantly whenever the direct pathway is efficient, the presence of indirect pathways is detrimental to the overall rate of ISC as they provide a slower alternative pathway. Our results provide a detailed insight into the mechanism of intersystem crossing in these complexes and will greatly facilitate the design of new higher performing molecules.

Carbene-metal-amides (CMAs) are a promising family of donor-bridge-acceptor molecular charge-transfer emitters for organic light-emitting diodes (OLEDs). Here a universal approach is introduced to tune the energy of their charge-transfer emission. A shift of up to 210 meV is achievable in the solid state via dilution in a polar host matrix. The origin of this shift has two components: constraint of thermally activated triplet diffusion, and electrostatic interactions between the guest molecules and the polar host. This allows the emission of mid-green CMA archetypes to be blue shifted without chemical modifications. Monte-Carlo simulations based on a Marcus-type transfer integral successfully reproduce the concentration- and temperature-dependent triplet diffusion process, and reveal a substantial shift in the ensemble density of states in polar hosts. In gold-bridged CMAs this substantial shift does not lead to a significant change in luminescence lifetime, thermal activation energy, reorganisation energy or intersystem crossing rate. These discoveries thus offer new experimental and theoretical insight in to the coupling between the singlet and triplet manifolds in these materials. Similar emission tuning can be achieved in related materials where chemical modification is used to modify the charge-transfer energy.

The nature of carbene–metal–amide (CMA) photoluminescence in the solid state is explored through spectroscopic and quantum-chemical investigations on a representative Au-centered molecule. The crys...

Abstract: It has been previously found that through anestablished synthesis of the macrocycle boron subnaphthalocyanine (BsubNc) thatrandom bay-position chlorination occurs and results in a mixed alloyedcomposition that cannot be separated; called chloro-(chloron)-boronsubnaphthalocyanines (Cl-ClnBsubNcs). Through modifications of the syntheticmethod, amounts of the average bay-position chlorination can be varied. Cl-ClnBsubNcsare fluorescent and therefore here we explore the effect of the amount of bay-positionchlorination on the photoluminescent and electroluminescent properties of Cl-ClnBsubNcs.Distinct from previous reports detailing the positive impact of higher average bay-positionchlorination, we find that the photophysical processes important to OLEDsimprove with lower average bay-position chlorination. A higher degree of bay-positionchlorine shows higher nonradiative recombination rates, lower photoluminescencequantum efficiencies and a basic OLEDs exhibits a greater host emission fraction,implying less effective energy transfer. These results advance the considerationof subnaphthalocyanines for light-emitting and optoelectronic applications.

Organic emitters exhibiting delayed fluorescence (DF) are promising luminescent materials for next-generation organic light-emitting diodes (OLEDs). Faster intersystem crossing rates and shorter emission lifetimes can be achieved in luminescent molecules through the incorporation of heavy atoms, which enhance spin-orbit coupling and promote intersystem crossing between singlet and triplet states. DF molecules often contain a sulfur atom, and reports of selenium-containing DF OLEDs also exist. However, the literature lacks a direct exploration of the effect of spin-orbit coupling on reverse intersystem crossing in a delayed fluorescence emitter by the substitution of selenium for sulfur. Here we show that substitution of selenium for sulfur in a modified thioxanthenone-triphenylamine analogue increases the rate of forward intersystem crossing by a factor of over 250 and the rate of reverse intersystem by a factor of 22. We attribute the increased rates to enhanced spin-orbit coupling from heavy atom substitution, and computational and electron spin resonance studies support this. This work provides an insight into future molecular design strategies for heavy-atom-containing, DF emitters.

The present invention provides complexes of the formula (L)M(X), in which M is a metal atom selected from copper, silver and gold.; L is a carbene ligand; and X is a monoanionic ligand. The complexes are useful as light emitters in the emissive zone of light-emitting devices such as OLEDs. The present invention also provides organometallic complexes which exhibit RASI photoemission, and the use of the same in light emitting devices such as OLEDs.

Conformationally flexible "Carbene-Metal-Amide" (CMA) complexes of copper and gold have been developed based on a combination of sterically hindered cyclic (alkyl)(amino)carbene (CAAC) and 6- and 7-ring heterocyclic amide ligands. These complexes show photoemissions across the visible spectrum with PL quantum yields of up to 89% in solution and 83% in host-guest films. Single crystal X-ray diffraction and photoluminescence (PL) studies combined with DFT calculations indicate the important role of ring structure and conformational flexibility of the amide ligands. Time-resolved PL shows efficient delayed emission with sub-microsecond to microsecond excited state lifetimes at room temperature, with radiative rates exceeding 10(6) s(-1). Yellow organic light-emitting diodes (OLEDs) based on a 7-ring gold amide were fabricated by thermal vapor deposition, while the sky-blue to warm-white mechanochromic behavior of the gold phenothiazine-5,5-dioxide complex enabled fabrication of the first CMA-based white light-emitting OLED.

The original version of this Article contained an error in the spelling of the author Dan Credgington, which was incorrectly given as Dan Credington. This has now been corrected in both the PDF and HTML versions of the Article.

Harnessing the near-infrared (NIR) region of the electromagnetic spectrum is exceedingly important for photovoltaics, telecommunications, and the biomedical sciences. While thermally activated delayed fluorescent (TADF) materials have attracted much interest due to their intense luminescence and narrow exchange energies (ΔEST), they are still greatly inferior to conventional fluorescent dyes in the NIR, which precludes their application. This is because securing a sufficiently strong donor–acceptor (D–A) interaction for NIR emission alongside the narrow ΔEST required for TADF is highly challenging. Here, we demonstrate that by abandoning the common polydonor model in favor of a D–A dyad structure, a sufficiently strong D–A interaction can be obtained to realize a TADF emitter capable of photoluminescence (PL) close to 1000 nm. Electroluminescence (EL) at a peak wavelength of 904 nm is also reported. This strategy is both conceptually and synthetically simple and offers a new approach to the development of future NIR TADF materials.

We combine absorption and fluorscence spectroscopy experiments and theoretical modeling to specifically examine the role of termini interactions on the optical properties.Optical absorption and fluorescence is measured for a six-chain amino acid 2Y3J (AIIGLM) which forms a segment of the full amyloid beta 1-40. In order to explore the sensitivity of the optical properties to the termini interactions, the experiments were repeated by acetylating the N-terminus.Although atomic force microscopy experiments indicate the formation of some form of fibrilar or crystal aggregates in both systems, the optical properties are strikingly different - acetylation significantly reduces optical activity between 280-350 nm.

Light-emitting carbene-metal amide complexes bearing first- and second-generation carbazole dendron ligands are reported, (L-Ad)M(G(n)), (M = Cu and Au; G(n) carbazole dendrimer generation, where n = 1 and 2; L-Ad = adamantyl-substituted cyclic (alkyl)(amino)carbene). The thermal stability of the complexes increases with each dendrimer generation. Cyclic voltammetry indicates that the highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels are largely unaffected by the size of the dendron, while first reduction and oxidation processes show a quasi-reversible character. The gold complexes in toluene at room temperature show photoluminescent quantum yields of up to 51.5% for the first and 78% for the second generation. Varied temperature transient photoluminescence decay is consistent with a thermally activated process, indicating a delayed fluorescence-type emission mechanism. Neat films show excited state lifetimes composed of prompt and dominant sub-microsecond delayed components, with radiative constants of up to 10(6) s(-1). Solution-processed organic light-emitting diodes for first-generation copper and gold dendrimers (L-Ad)M(G(1)) have been fabricated with external quantum efficiencies of 5.5% for copper and 10.3% for gold at practical brightness.