A Tri-Spiral-Mediated Spatial Hybrid LRCT/SRCT Strategy for High-Efficiency Narrowband Blue Emitters

The conventional hybrid strategy that directly links long-range charge-transfer (LRCT) and short-range charge-transfer (SRCT) units through a single bond inevitably induces an uncontrollable electron push-pull effect, resulting in emission redshift and spectral broadening. In this study, we propose a spiro-mediated spatial decoupling strategy that bridges an LRCT-type donor-acceptor fragment and an SRCT-type multiple-resonance (MR) fragment through a nonconjugated tri-spiral skeleton for the first time. This design effectively interrupts the π-conjugation between the two units, allowing the LRCT fragment to introduce additional reverse intersystem crossing (RISC) channels without perturbing the MR core. As a result, a 16-fold enhancement in RISC rate is achieved relative to the MR prototype while preserving narrowband emission. TRZN//NBO exhibits an emission peak of 473 nm with a narrow full width at half maximum of 24 nm in toluene and a fast RISC rate of 1.26 × 10⁵ s^-1. The corresponding device achieves a maximum external quantum efficiency (EQE) of 36.1%, retaining high EQEs of 28.2% and 21.0% at luminance of 100 and 1000 cd m^-2, respectively. These results demonstrate that the spiro-mediated spatial hybrid LRCT/SRCT strategy offers a promising route to circumvent the trade-off between efficiency and color purity in narrowband emitters.