Delayed fluorescence and room temperature phosphorescence from a liquid arene

Delayed emission (DF) of fluorescence is generally observed either in solution or in the crystalline state. In the latter, well‐defined intermolecular interactions may play a significant role in defining the emission characteristics. Here, we present a trialkoxy‐homotruxene that is liquid at room temperature and compare its emission behavior with that of a crystalline analog containing the same π‐electron system. The DF observed is due to triplet‐triplet annihilation (TTA) and persists at low temperatures (90 K). Accompanied by slightly shorter phosphorescence and DF lifetimes, the singlet‐triplet energy gap increased by 4% compared to the crystalline homolog. The replacement of methyl groups with racemic branched alkoxy chains in homotruxene derivatives proves efficient in suppressing crystallization without significantly altering DF. In neat films, the compound exhibited TTA‐DF at room temperature, phosphorescence lasting up to 50 ms and Photoluminescence Quantum Yield (PLQY) of 24%. Thus, TTA‐DF persists in a single‐component isotropic liquid phase, showing both molecular and aggregate emissions, only slightly affected by the absence of periodic molecular stacking.