Unlocking Dual Functionality in Triazine-Based Emitters: Synergistic Enhancement of Two-Photon Absorption and...

The simultaneous realization of two-photon absorption (2PA) and thermally activated delayed fluorescence (TADF) in a single molecular system remains challenging due to an inherent trade-off in their molecular design requirements. In this study, we present a strategy to enhance both properties by introducing electron-withdrawing substituents into the CzTRZ scaffold, thereby leveraging an electron-withdrawing-enhanced intramolecular charge transfer (EWICT) character. The incorporation of TRZCF₃ and TRZCN units effectively enhances the charge transfer (CT) character of CzTRZ, resulting in high 2PA cross-sections (156 GM for CzTRZCF₃ and 200 GM for CzTRZCN) and a reduced singlet-triplet energy gap (ΔE_ST = E_S1 - E_T1). Computational and experimental studies reveal that incorporating TRZCF₃ and TRZCN units selectively stabilizes the S₁ state and reduces ΔE_ST, significantly facilitating the reversed intersystem crossing (RISC) process. Notably, 1c exhibits the fastest RISC rate (k_RISC), leading to superior TADF properties and an external quantum efficiency (EQE) of 13.5% in OLEDs. Moreover, a relatively high two-photon brightness of 174 GM is estimated for 1c. These findings demonstrate a rational molecular design strategy for the synergistic enhancement of 2PA cross-sections and excellent OLED performance, paving the way for applications in advanced imaging probes and organic semiconductors.