Three-state-involving vibronic resonance is a key to enhancing reverse intersystem crossing dynamics of organoboron-based ultrapure blue emitters

Inkoo Kim, Kwuang Hyun Cho, Soon Ok Jeon, Won-Joon Son, Dongwook Kim, Young Min Rhee, Inkook Jang, Hyeonho Choi, Dae Sin Kim

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22nd May 20

The recently developed narrow-band blue-emitting organoboron chromophores have now become one of the most important components for constructing efficient organic light emitting diodes (OLEDs). While they basically emit through fluorescence, they are also known for showing substantial thermally activated delayed fluorescence (TADF) even with a relatively large singlet-triplet gap (DEST). Indeed, understanding the reverse intersystem crossing (RISC) dynamics behind this peculiar TADF will allow judicious molecular designs toward achieving better performing OLEDs. Explaining the underlying nonadiabatic spin-flip mechanism, however, has often been equivocal with the neglect of higher order effects beyond the simple direct spin-orbit coupling. Here, we apply a full second-order spin-vibronic model to elaborate the underlying physics of RISC in a typical organoboron emitter and show that a vibronic resonance that orchestrates three electronic states together is playing a major role in enhancing RISC. Through semiclassical quantum dynamics simulations, we further show that the geometry dependent non-Condon coupling in the triplet state manifold that oscillates with the frequency DEST/hbar is the main driving force behind the peculiar resonance enhancement. Our investigation may provide a new guide for future blue emitting molecule developments.

Read in full at ChemRxiv.

This is an abstract of a preprint hosted on an independent third party site. It has not been peer reviewed but is currently under consideration at Nature Communications.

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