Understanding Spin-Triplet Excited States in Carbene-Metal-Amides.

Carbene-metal-amides (CMAs) are emerging delayed fluorescence materials for organic light-emitting diode (OLED) applications. CMAs possess fast, efficient emission owing to rapid forward and reverse intersystem crossing (ISC) rates. The resulting dynamic equilibrium between singlet and triplet spin manifolds distinguishes CMAs from most purely organic thermally activated delayed fluorescence emitters. However, direct experimental triplet characterization in CMAs is underutilized, limiting our detailed understanding of the ISC mechanism. In this work, we combine time-resolved spectroscopy with tuning of state energies through environmental polarity and metal substitution, focusing on the interplay between charge-transfer (3CT) and local exciton (3LE) triplets. Unlike previous photophysical work, we investigate evaporated host : guest films of CMAs and small-molecule hosts for increased device relevance. Transient absorption reveals an evolution in the triplet excited-state absorption (ESA) consistent with a change in orbital character between hosts with differing dielectric constants. Using quantum chemical calculations, we simulate ESAs of the lowest triplet states, highlighting the contribution of only 3CT and donor-moiety 3LE states to spectral features, with no strong evidence for a low-lying acceptor-centered 3LE. Thus, our work provides a blueprint for understanding the role of triplet excited states in CMAs which will enable further intelligent optimization of this promising class of materials.

Fast Transfer of Triplet to Doublet Excitons from Organometallic Host to Organic Radical Semiconductors.

Spin triplet exciton formation sets limits on technologies using organic semiconductors that are confined to singlet-triplet photophysics. In contrast, excitations in the spin doublet manifold in organic radical semiconductors can show efficient luminescence. Here the dynamics of the spin allowed process of intermolecular energy transfer from triplet to doublet excitons are explored. A carbene-metal-amide (CMA-CF3) is employed as a model triplet donor host, since following photoexcitation it undergoes extremely fast intersystem crossing to generate a population of triplet excitons within 4 ps. This enables a foundational study for tracking energy transfer from triplets to a model radical semiconductor, TTM-3PCz. Over 74% of all radical luminescence originates from the triplet channel in this system under photoexcitation. It is found that intermolecular triplet-to-doublet energy transfer can occur directly and rapidly, with 12% of triplet excitons transferring already on sub-ns timescales. This enhanced triplet harvesting mechanism is utilized in efficient near-infrared organic light-emitting diodes, which can be extended to other opto-electronic and -spintronic technologies by radical-based spin control in molecular semiconductors.

Deep-Blue and Fast Delayed Fluorescence from Carbene-Metal-Amides for Highly Efficient and Stable Organic Light-Emitting Diodes.

Linear gold complexes of the "carbene-metal-amide" (CMA) type are prepared with a rigid benzoguanidine amide donor and various carbene ligands. These complexes emit in the deep-blue range at 424 and 466 nm with 100% quantum yields in all media. The deep-blue thermally activates delayed fluorescence originates from a charge transfer state with an excited state lifetime as low as 213 ns, resulting in fast radiative rates of 4.7 × 106 s-1. The high thermal and photo-stability of these carbene-metal-amide (CMA) materials enabled the authors to fabricate highly energy-efficient organic light-emitting diodes (OLED) in host-guest architectures. Deep-blue OLED devices with electroluminescence at 416 and 457 nm with practical external quantum efficiencies of up to 23% at 100 cd m-2 with excellent color coordinates CIE (x; y) = 0.16; 0.07 and 0.17; 0.18 are reported. The operating stability of these OLEDs is the longest reported to date (LT50 = 1 h) for deep-blue CMA emitters, indicating a high promise for further development of blue OLED devices. These findings inform the molecular design strategy and correlation between delayed luminescence with high radiative rates and CMA OLED device operating stability.

Prognostic Impact of Sinus Rhythm in Atrial Fibrillation Patients: Separating Rhythm Outcomes From Randomized Strategy Findings From the CABANA Trial.

BACKGROUND: Clinically detected atrial fibrillation (AF) is associated with a significant increase in mortality and other adverse cardiovascular events. Since the advent of effective methods for AF rhythm control, investigators have attempted to determine how much these adverse prognostic AF effects could be mitigated by the restoration of sinus rhythm (SR) and whether the method used mattered. METHODS: The CABANA trial (Catheter Ablation versus Antiarrhythmic Drug Therapy for Atrial Fibrillation) randomized 2204 AF patients to ablation versus drug therapy, of which 1240 patients were monitored in follow-up using the CABANA ECG rhythm monitoring system. To assess the prognostic benefits of SR, we performed a prespecified analysis using Cox survival modeling with heart rhythm as a time-dependent variable and randomized treatment group as a stratification factor. RESULTS: In the 1240 patient study cohort, 883 (71.2%) had documented AF at some point during their postblanking follow-up. Among the 883 patients, 671 (76.0%) experienced AF within the first year of postblanking follow-up, and 212 (24.0%) experienced their first AF after ≥1 year of postblanking follow-up. The primary CABANA end point (death, disabling stroke, serious bleeding, or cardiac arrest) occurred in 95 (10.8%) of the 883 patients with documented AF and in 29 (8.1%) of the 357 patients with no AF recorded during follow-up. In multivariable time-dependent analysis, the presence of SR (compared with non-SR) was associated with a significantly reduced risk of the primary end point (adjusted hazard ratio, 0.57 [95% CI, 0.38-0.85]; P=0.006; independent of treatment strategy [ablation versus drugs]). Corresponding results for all-cause mortality were adjusted hazard ratio of 0.59 [95% CI, 0.35-1.01]; P=0.053). CONCLUSIONS: In patients in the CABANA trial with detailed long-term rhythm follow-up, increased time in SR was associated with a clinically consequential decrease in mortality and other adverse prognostic events. The predictive value of SR was independent of the therapeutic approach responsible for reducing the burden of detectable AF. REGISTRATION: URL: https://clinicaltrials.gov; Unique Identifier: NCT00911508.