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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 ( 3 CT) and local exciton ( 3 LE) 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 3 CT and donor-moiety 3 LE states to spectral features, with no strong evidence for a low-lying acceptor-centered 3 LE. 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., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Organic solar cells are approaching power conversion efficiencies of other thin-film technologies. However, in order to become truly market competitive, the still substantial voltage losses need to be reduced. Here, the synthesis and characterization of four novel arylamine-based push-pull molecular donors was described, two of them exhibiting a methyl group at the para-position of the external phenyl ring of the arylamine block. Assessing the charge-transfer state properties and the effects of methylation on the open-circuit voltage of the device showed that devices based on methylated versions of the molecular donors exhibited reduced voltage losses due to decreased non-radiative recombination. Modelling suggested that methylation resulted in a tighter interaction between donor and acceptor molecules, turning into a larger oscillator strength to the charge-transfer states, thereby ensuing reduced non-radiative decay rates., (© 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

π-Conjugated push-pull molecules based on triphenylamine and 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) have been functionalized with different terminal arene units. In solution, these highly TCBD-twisted systems showed a strong internal charge transfer band in the visible spectrum and no detectable photoluminescence (PL). Photophysical and theoretical investigations revealed very short singlet excited state deactivation time of ≈10 ps resulting from significant conformational changes of the TCBD-arene moiety upon photoexcitation, opening a pathway for non-radiative decay. The PL was recovered in vacuum-processed films or when the molecules were dispersed in a PMMA matrix leading to a significant increase of the excited state deactivation time. As shown by cyclic voltammetry, these molecules can act as electron donors compared to C 60 . Hence, vacuum-processed planar heterojunction organic solar cells were fabricated leading to a maximum power conversion efficiency of ca. 1.9 % which decreases with the increase of the arene size., (© 2020 Wiley-VCH GmbH.)