摘要
Precise control over the emissive excited states of luminophores is crucial for advancing high-performance optoelectronic materials.Herein,we present a facile strategy for tuning the emissive excited states of o-carborane-functionalized B,N-doped multi-resonance thermally activated delayed fluorescence(MR-TADF)compounds through steric modulation of 2-R substituents.A series of 2-R-o-carboranyl MR-TADF compounds,denoted DtBuCzB-CBR,were synthesized and characterized with substituents of varying steric demand at the 2-position of the o-carborane cage(R=H(1),Me(2),iBu(3),and SiMe3(TMS,4)).Single-crystal X-ray analyses of compounds 2 and 4 revealed a nearly perpendicular orientation of the o-carboranyl C-C bond relative to the MR core plane,with compound 4 showing greater C-C bond elongation and structural distortion than 2.Notably,the compounds exhibit either single(1)or dual emission(2-4)in both solution and rigid states,depending on the steric bulk of the 2-R substituent.Theoretical calculations suggest that the single emission originates from a locally excited short-range charge transfer(SRCT)state confined within the MR core,whereas dual emission arises from both the SRCT state and a lower-energy hybridized local and charge transfer(HLCT)state,facilitated by electronic coupling between the MR core and the o-carborane unit.The emergence and persistence of the emissive HLCT state correlate with increased steric hindrance at the 2-position,which induces elongation of the o-carboranyl C-C bond and restricts cage rotation in the excited state.These findings provide a new design principle for o-carborane-based luminophores with tunable excited-state emission characteristics.
基金
supported by the Basic Science Research Program funded by the Ministry of Science and ICT(MSIT)(RS-2025-00514431 and RS-2025-02216980 for M.H.L.and NRF-2021R1A2C1009191 and RS-2024-00407859 for J.J.)through the National Research Foundation of Korea(NRF)
financial support from the Ulsan RISE Center(2025-RISE-07-001).
