advantages. This limitation originates from intrinsic degradation of the organic materials because degradation byproducts increase the driving voltage, accelerate non-emissive channels, and deteriorate the color purity of an electroluminescence device. [1,2] Thus, suppressing intrinsic degradation has been the focus of particular interest from both scientific and technological perspectives. Pioneering studies indicated that intrinsic degradation is mediated by an exciton or a polaron, which are the key elements for normal operation of OLEDs. [3-9] This unimolecular degradation becomes salient for blue-emissive devices involving high-energy excitons and for unbalanced devices that permit charge carrier leakage. Later studies suggested the occurrence of bimolecular degradation mechanisms. [10-15] An encounter of two long-lived triplet excitons may produce a highly unstable singlet exciton. The bimolecular upconversion often enables exergonic access to dissociative states where degradation occurs. Decomposition also proceeds through an annihilation between a polaron and a triplet exciton. This bimolecular annihilation can yield an excited-state polaron that is susceptible to bond cleavage or can lead to the formation of dimeric byproducts. These mechanistic understandings are valuable because they offer novel strategies for improving the operational lifetime of OLEDs. For example, decreasing the concentration and lifetime of excitons has been demonstrated to be an effective approach to extending device longevity. [11,16-20] Alternatively, balancing charge carrier densities and delocalizing an exciton-formation zone could also avoid the destructive exciton-polaron annihilation (EPA). [21-24] In a recent study, Crǎciun and co-workers reported that EPA involved excitons generated through Shockley-Read-Hall (SRH) recombination between trapped positive polarons and free negative polarons in polymer emitting layers. [25] Therefore, intrinsic degradation could be suppressed by avoiding SRH recombination or by facilitating Langevin recombination. Duan's group reached an opposing conclusion. [26,27] They found that Langevin recombination on hosts was detrimental to device stability, because dark and longlived triplet excitons of a host would be more susceptible to the aforementioned hazardous bimolecular annihilation The operational lifetime of organic light-emitting devices (OLEDs) is governed primarily by the intrinsic degradation of the materials. Therefore, a chemical model capable of predicting the operational stability is highly important. Here, a degradation model for OLEDs that exhibit thermally activated delayed fluorescence (TADF) is constructed and validated. The degradation model involves Langevin recombination of charge carriers on hosts, followed by the generation of a polaron pair through reductive electron transfer from a dopant to a host exciton as the initiation steps. The polarons undergo spontaneous decomposition, which competes with ultrafast recovery of the intact materials through charge recombination....

Electrides, which have excess anionic electrons, are solid-state sources of solvated electrons that can be used as powerful reducing agents for organic syntheses. However, the abrupt decomposition of electrides in organic solvents makes controlling the transfer inefficient, thereby limiting the utilization of their superior electron-donating ability. Here, we demonstrate the efficient reductive transformation strategy which combines the stable two-dimensional [Gd2C]2+·2e– electride electron donor and cyclometalated Pt­(II) complex photocatalysts. Strongly localized anionic electrons at the interlayer space in the [Gd2C]2+·2e– electride are released via moderate alcoholysis in 2,2,2-trifluoroethanol, enabling persistent electron donation. The Pt­(II) complexes are adsorbed onto the surface of the [Gd2C]2+·2e– electride and rapidly capture the released electrons at a rate of 107 s–1 upon photoexcitation. The one-electron-reduced Pt complex is electrochemically stable enough to deliver the electron to substrates in the bulk, which completes the photoredox cycle. The key benefit of this system is the suppression of undesirable charge recombination because back electron transfer is prohibited due to the irreversible disruption of the electride after the electron transfer. These desirable properties collectively serve as the photoredox catalysis principle for the reductive generation of the benzyl radical from benzyl halide, which is the key intermediate for dehalogenated or homocoupled products.

Organic light-emitting devices (OLEDs) containing organic molecules that exhibit thermally activated delayed fluorescence (TADF) produce high efficiencies. One challenge to the commercialization of the TADF OLEDs that remains to be addressed is their operational stability. Here we investigate the molecular factors that govern the stability of various archetypal TADF molecules based on a cycloamino donor–acceptor platform. Our results reveal that the intrinsic stability depends sensitively on the identity of the cycloamino donors in the TADF compounds. The rates and photochemical quantum yields of the degradation are positively correlated with the operation lifetimes of the devices. Our research shows that the stability is governed by the conformeric heterogeneity between the pseudo-axial and pseudo-equatorial forms of the cycloamino donor. Spontaneous bond dissociation occurs in the former (i.e., the pseudo-axial form), but the cleavage is disfavored in the pseudo-equatorial form. These findings provide valuable insights into the design of stable TADF molecules.

A chemical model capable of predicting the operational stability for organic light‐emitting devices is established, as reported by Dongho Kim, Jun Yeob Lee, Youngmin You, and co‐workers in article number 2003832. This model involves Langevin recombination, followed by electron transfer from a dopant to a host exciton, as the key degradation step. The research disentangles the chemical processes in the degradation and provides a useful foundation for enhancing the operational stability of electroluminescence devices.