Role of Vibronic Structure and Spectral Separation in TADF Emitters for Efficient Organic Lasers

Abstract Thermally activated delayed fluorescence (TADF) molecules offer significant promise for organic laser applications due to their potential triplet harvesting. Encouragingly, localized charge‐transfer characteristics within rigid skeletons, such as multiple‐resonance (MR) effects and locked donor–acceptor (D–A) interactions, are particularly attractive as they enable both large oscillator strengths and TADF properties. In this study, representative boron/nitrogen (B/N)‐containing TADF molecules are investigated to reveal the crucial role of Stokes shifts in tuning absorption–emission overlap. This overlap influences self‐absorption losses and ultimately reorganizes the transition mode for lasing output. Notably, although ν‐DABNA exhibits the highest stimulated emission cross‐section coefficient (σ_em), it results in lasing from the 0−1 vibronic transition with the highest lasing threshold (12.0 µJ cm⁻²) owing to its strong steady‐state and excited‐state absorption losses. In contrast, PXZN‐B, featuring a locked D–A skeleton with a smaller σ_em, achieves a lower lasing threshold of 3.9 µJ cm⁻² by leveraging a larger Stokes shift, which minimizes reabsorption losses and facilitates efficient light amplification at the dominant 0−0 transition. These findings highlight the importance of balancing oscillator strength enhancement with favorable spectral separation to modulate the ideal transition mode for efficient organic lasing.