Achieving highly efficient long-wavelength phosphorescence emission of large singlet-triplet energy gap materials by host-guest doping

High-efficiency long-wavelength phosphorescence emissions of large singlet-triplet energy gap (ΔE_ST) materials are essential for applications in biology and display. However, few long-wavelength phosphorescence emissions of large ΔE_ST materials have been reported due to the weak spin-orbit coupling (SOC) and strong non-radiative transitions. Herein, we develop a strategy to achieve highly efficient long-wavelength room temperature phosphorescence (RTP) emission of large ΔE_ST materials, which display bright red RTP emission with above 400 µs lifetime and 6.5% phosphorescent quantum efficiency. Our experiments and theoretical calculations reveal that the fishbone-like packing and the zig-zag interactions provide favorable conditions for suppressing the non-radiative transitions of triplet state excitons, and heavy atoms effectively promote the intersystem crossing (ISC) process for highly efficient long-wavelength phosphorescence emission. The universality of the method for highly efficient long-wavelength RTP emission of large ΔE_ST materials was further investigated in various guests. Moreover, these materials with large ΔE_ST manifest the advantages of large color contrast on the display and utilization potentiality in information encryption. This strategy paves the way for the high contrast display and development of information encryption with RTP emission.