Open Access

Annika Morgenstern, Jonas Weiser, Lucas Schreier, Konstantin Gabel, Tom Gabler, Alexander Ehm, Daniel Beer, Nadine Schwierz, Ulrich T. Schwarz, Kirsten Zeitler, Carsten Deibel, Dietrich R. T. Zahn, Christian Wiebeler, Georgeta Salvan

• The determination of transport mechanisms in organic light-emitting diodes (OLEDs) is crucial for optimizing device performance. Magnetic field measurements enable the differentiation of spin state interconversion mechanisms, but data interpretation remains challenging. Here, experimental and theoretical investigations are combined to provide a comprehensive understanding of the underlying processes. This study systematically compares three cyanoarene-based emitters with different singlet–triplet gaps (ΔEST) to explore factors influencing reverse intersystem crossing (RISC). The comparison of all-1H and all-2H 4CzIPN isotopologues confirms that RISC is governed by spin-orbit coupling (SOC) rather than hyperfine interactions. Magnetic field-dependent measurements reveal that charge transport in OLED devices is driven by triplet-charge annihilation in 3CzClIPN and 4CzIPN, while triplet–triplet annihilation dominates for 5CzBN. Theoretical calculations further indicate that SOC-mediatedThe determination of transport mechanisms in organic light-emitting diodes (OLEDs) is crucial for optimizing device performance. Magnetic field measurements enable the differentiation of spin state interconversion mechanisms, but data interpretation remains challenging. Here, experimental and theoretical investigations are combined to provide a comprehensive understanding of the underlying processes. This study systematically compares three cyanoarene-based emitters with different singlet–triplet gaps (ΔEST) to explore factors influencing reverse intersystem crossing (RISC). The comparison of all-1H and all-2H 4CzIPN isotopologues confirms that RISC is governed by spin-orbit coupling (SOC) rather than hyperfine interactions. Magnetic field-dependent measurements reveal that charge transport in OLED devices is driven by triplet-charge annihilation in 3CzClIPN and 4CzIPN, while triplet–triplet annihilation dominates for 5CzBN. Theoretical calculations further indicate that SOC-mediated RISC in 3CzClIPN and 4CzIPN can additionally occur via a T2 intermediate state with an activation energy distinct from ΔEST. A temperature-dependent analysis of the devices was conducted to quantify this activation energy and compare it with the computational findings. These findings establish key correlations between activation energy, spin dynamics, and magnetic field effects in TADF emitters, advancing the understanding of excitonic processes in OLEDs.…