High-Efficiency, Long-Lived, Multicolor Tunable Pure Organic Materials for Dual Fluorescent-Phosphorescent Emission at Room Temperature

Currently, numerous afterglow materials often suffer from low phosphorescence quantum yields (ΦPh) and are confined to a singular luminescent color. In this study, we devised an approach by incorporating four distinct carbazole derivative guest molecules, featuring varying degrees of halogen substitution and naphthalene group substitution sites, into β-estradiol host molecules through high-temperature melt doping to create four exceptional organic composites. Remarkably, all four materials exhibit exceptional characteristics, including prolonged afterglow lifetimes and ultrahigh afterglow quantum yields, with the pinnacle phosphorescence lifetime soaring to 904.76 ms and the peak phosphorescence quantum yield achieving a remarkable 40.0%. Notably, even without heavy atom incorporation, the phosphors managed to attain a ΦPh of 18.0%, underscoring their unique properties. Furthermore, our experiments unveiled an intriguing phenomenon: rather than a single fluorescence or phosphorescence emission, these materials exhibit dual-emission characteristics, encompassing both fluorescence and phosphorescence. The versatility in luminescence color manipulation was further demonstrated by adjusting the temperature and excitation wavelength, offering unparalleled flexibility. Moreover, the fluorescence hues of these materials could be finely tuned by varying the number of halogen atoms, adding another layer of color tunability. Theoretical calculations provided valuable insights, showing that changes in the number of bromine substitutions and the substitution positions of the naphthalene group significantly affect the molecule's spin–orbit coupling constants and the nature of its excited states. This understanding not only highlights the molecular mechanisms behind the observed luminescence properties but also provides a roadmap for the future design and optimization of such advanced luminescent materials.