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Decoding Vibrational Contributions and Exciton Dynamics in TADF Emitters for Enhanced OLED Efficiency
No full textThermally activated delayed fluorescence (TADF) compounds play a pivotal role in enhancing the efficiency of organic light-emitting diodes (OLEDs) by enabling effective triplet exciton utilization, often facilitated by vibrational assistance. While multiresonant TADF systems benefit from rigid planar structures that suppress nonradiative decay, traditional donor-acceptor-donor (D-A-D) systems are more prone to nonradiative losses with their flexible single-bond connections. This study investigates three structurally similar D-A-D TADF compounds with distinct external quantum efficiencies to uncover the factors influencing their performance. Our analysis identifies specific vibrational modes that either enhance radiative transitions or contribute to nonradiative decay, emphasizing the critical role of vibrational dynamics. Using Huang-Rhys factor and exciton-phonon coupling, we demonstrate how these vibrational modes govern exciton dynamics. The Herzberg-Teller effect emerges as a key mechanism driving thermally activated performance, with vibrational corrections significantly improving the accuracy of rate predictions. The computed radiative and nonradiative rates show satisfactory agreement with experimental data, validating the robustness of our computational protocol. These findings provide actionable insights into the molecular design of TADF emitters, offering strategies to optimize OLED performance by balancing the interplay between vibrational dynamics and electronic transitions
Temperature-Dependent Raman Spectroscopy Analysis of Epitaxially Grown Ge0.91Sn0.09 on GaAs (001) Substrate
No full textAbstract: We report on the epitaxial growth of Ge0.91Sn0.09 alloy epilayers on a GaAs (001) substrate by low-temperature molecular beam epitaxy. Temperature-dependent Raman measurements were used to investigate the behavior and stability of Sn in Ge1–xSnx grown on GaAs by examining the behavior of the longitudinal optical phonon modes originating from both the Ge1–xSnx epilayers and the GaAs substrate. The Raman data reveals improved crystalline quality and increased Sn content in the Ge1–xSnx epilayer as the temperature is increased from 100 to 580 K. However, at a temperature of about T = 620 K, the mobility and segregation of Sn in the Ge1–xSnx epilayers dramatically increases. This behavior is similar to reports of Sn mobility and potential segregation from Ge1–xSnx grown on both Ge and Si substrates, despite differences in atom chemistry between Ge1–xSnx and the different substrates. Likely, the transition temperature for which Sn becomes mobile in Ge1–xSnx is dominated by its dependence on the bonding between Ge and Sn and level of strain in the Ge matrix
On the prevalence and usage of commit signing on GitHub: a longitudinal and cross-domain study
No full textGitHub is one of the most widely used public code development platform. However, the code hosted publicly on the platform is vulnerable to commit spoofing that allows an adversary to introduce malicious code or commits into the repository by spoofing the commit metadata to indicate that the code was added by a legitimate user. The only defense that GitHub employs is the process of commit signing, which indicates whether a commit is from a valid source or not based on the keys registered by the users.
In this work, we perform an empirical analysis of how prevalent is the use of commit signing in commonly used GitHub repositories. To this end, we build a framework that allows us to extract the metadata of all prior commits of a GitHub repository, and identify what commits in the repository are verified. We analyzed 60 open-source repositories belonging to four different domains -- web development, databases, machine learning and security -- using our framework and study the presence of verified commits in each repositories over five years. Our analysis shows that only ~10% of all the commits in these 60 repositories are verified. Developers committing code to security-related repositories are much more vigilant when it comes to signing commits by users.
We also analyzed different Git clients for the ease of commit signing, and found that GitKraken provides the most convenient way of commit signing whereas GitHub Web provides the most accessible way for verifying commits. During our analysis, we also identified an unexpected behavior in how GitHub handles unverified emails in user accounts preventing legitimate owner to use the email address. We believe that the low number of verified commits may be due to lack of awareness, difficulty in setup and key management. Finally, we propose ways to identify commit ownership based on GitHub's Events API addressing the issue of commit spoofing
A bismuth-based analogue of the π-allyl cation
No full textThe π-allyl cation is a three-carbon system featuring a positive charge and a conjugated π-system. There is interest in preparing heavier π-allyl cation analogues, but the synthesis of these is challenging. Now, a compound featuring a cationic triatomic bismuth-based core has been isolated and fully characterized
Disentangling Energy Transfer Pathways in Donor–Acceptor Dyads: A Molecular-Level Perspective for TADF OLED Applications
No full textA comprehensive understanding of the nonradiative energy transfer process is critical for advancing emitter design in organic light-emitting diodes (OLEDs). This study employs a multiscale computational approach integrating classical molecular dynamics, quantum chemical calculations, and kinetic Monte Carlo simulations to investigate a multiresonant (MR) emitter dyad (Cy-tmCPBN) in pure and doped film morphologies. Our results show that film morphology and molecular orientation critically influence energy transfer efficiency. In the pure film, tight molecular packing and favorable donor–acceptor alignment promote efficient intermolecular energy transfer. In contrast, doping with a donor host (Cy-tmCP)─which incorporates the same donor fragment as Cy-tmCPBN─introduces spatial dilution and disrupts molecular alignment, yielding reduced resonance energy transfer rates. Quantum mechanical analyses based on interfragment charge transfer and noncovalent interaction frameworks reveal that while the excitations are predominantly localized, weak yet non-negligible intermolecular electronic coupling in the pure film facilitates the observed energy transfer. These findings underscore the importance of tuning molecular organization and structural rigidity to control exciton behavior and optimize energy transfer in OLED emitter layers, aligning with ongoing efforts to improve device performance through rational molecular design
3D N = 1 supergravity from Virasoro TQFT: gravitational partition function and Out-of-time-order correlator
No full textIn this paper, we compute the partition functions of N = 1 SUGRA for different boundary topologies, i.e. punctured sphere and torus, using super-Virasoro TQFT. We use fusion and modular kernels of the super-Liouville theory to compute the necklace-channel conformal block and showcase formalism by proving that the inner product holds for superconformal blocks, defined as states in the Hilbert space. Finally, we compute the out-of-time-order correlator for the torus topology with superconformal primary insertions as matter using the tools of super-Virasoro TQFT and investigate its early-time behaviour
Computational Thinking Based STEM Art Exhibits
No full textMaking large-scale STEM exhibits can be a very engaging group activity for students across all ages. Apart from giving them a sense of accomplishment from completing the mammoth task of exhibit making, it also inspires them to think about the underlying algorithm that generated the design. In this paper, we describe exhibit designs based on pixel art using materials such as dice, bindis, Rubik’s cubes, strings, tessellation tiles, sticky notes, push-pins etc. We also share our experience and learnings from making 25+ different large scale portraits with students from elementary school to undergraduates. Affordable raw-materials and open-source tools make the designs accessible for use by educators in their schools
Correlating Ligand Properties with Photocatalytic Efficiency: A Computational Framework for Interface Engineering
No full textWe present the application of the Marcus-Hush formalism as a theoretical framework to investigate charge transfer dynamics in ligand-protected Au systems. By integrating key parameters such as energy level differences and electronic coupling, this approach enables the prediction of photocatalytic efficiency in electron-driven water splitting. Simulations of diverse ligand-functionalized AuNPs establish a clear correlation between charge transfer rates and hydrogen evolution, specifically for functionalized AuNPs bearing aromatic thiols with various para-substituents. Additionally, we extend this framework to selenol-substituted systems, revealing that while selenols perform comparably to thiols in some cases, they do not consistently enhance photocatalytic activity. Beyond electron-driven hydrogen production, we further explore the role of ligand chemistry in modulating hole transfer processes relevant to oxidative half-reactions. In this context, the OH-thiol ligand-functionalized AuNP emerges as the most effective photocatalyst for hole-driven reactions. Overall, this study provides a systematic methodology for screening and designing ligand-functionalized AuNP photocatalysts, offering mechanistic insights into how ligand properties govern photocatalytic performance