Silane-bridged donor-σ-acceptor dyads as exciplex host for efficient TADF OLEDs

초록

Silane-bridged host materials have attracted considerable attention for organic light-emitting diode (OLED) applications owing to their high thermal stability and structural versatility, while the sigma-bridge offers an effective platform for electronic decoupling between functional host units. However, most reported silane-based hosts rely on single-molecule architectures with unipolar charge-transport characteristics, which limits their applicability in solution-processed OLEDs. Herein, two silane-bridged donor-acceptor dyads (Si-PN1 and Si-PN2) incorporating a rigid diphenylsilane bridge were designed and synthesized, in which carbazole-based donor (D) and triazine-based acceptor (A) units are spatially separated to construct a D-sigma-A framework. Both host materials demonstrate remarkable thermal stability, as evidenced by decomposition temperatures above 540 degrees C and glass transition temperatures exceeding 150 degrees C, which contribute to their high morphological stability. In addition, they show good solubility, and the corresponding host-emitter blend films exhibit smooth and amorphous morphologies favorable for solution processing. The sigma-bridged dyad architecture leads to well-separated frontier molecular orbitals in thin films and small singlet-triplet energy gaps, enabling efficient reverse intersystem crossing associated with exciplex states that exhibit thermally activated delayed fluorescence (TADF) characteristics. Exciplex emission is observed at approximately 460 nm for Si-PN1 and is red-shifted to around 470 nm for Si-PN2, reflecting differences in donor-acceptor coupling and resonance effects arising from molecular design. Consequently, Si-PN2 exhibits a higher photoluminescence quantum yield and delivers superior device performance, achieving an external quantum efficiency of approximately 25% in solution-processed green TADFOLEDs. These results demonstrate that silane-bridged D-sigma-A systems represent a structurally distinct and photophysically robust molecular platform for solution-processable exciplex hosts in advanced OLED applications. Unlike conventional binary exciplex hosts, these systems eliminate phase separation issues by integrating donor and acceptor units within a single molecule.

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