Abnormal Anti‐Kasha Emission and TADF in Anionic Cycloarylenes

Abstract

AbstractIncorporation of non‐benzoid rings into cycloarylenes significantly alters their molecular geometry and optical behavior. Recently, we synthesized two ferrocene‐doped cycloarylenes, (CpFe)3‐1 and (CpFe)4‐2. However, the {FeCp} moieties in these architectures limited their optical properties. In this work, we report a reductive Fe─Cp bond cleavage approach that enables the removal of {FeCp} moieties efficiently, yielding two anionic cycloarylenes, 13– and 24–. Single crystal X‐ray diffraction analysis reveals different structure deformation between two charged species including molecular symmetry and π‐conjugation. Comprehensive spectroscopic analyses and theoretical calculations demonstrate that both 13– and 24– exhibit steady emission at 560 and 587 nm, respectively, with noticeable high quantum yields (59.70% and 84.99%). 13– violates Kasha's rule via a rare mixed emission from S2→S0 and S1'→S0, whereas 24– adheres to the conventional S1'→S0 decay. Furthermore, both compounds exhibit thermally activated delayed fluorescence (TADF) as the first example observed in cycloarylenes, with lifetimes reaching the millisecond scale. This work establishes alkali‐metal‐mediated reductive cleavage as an effective strategy to break Fe─Cp bond and provides new insight into the photophysical behavior of charged molecular nanocarbons, paving the way for the rational design of functional molecular materials.