Abnormal Anti-Kasha Emission and TADF in Anionic Cycloarylenes

Incorporation 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, 1^3- and 2^4-. 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 1^3- and 2^4- exhibit steady emission at 560 and 587 nm, respectively, with noticeable high quantum yields (59.70% and 84.99%). 1^3- violates Kasha's rule via a rare mixed emission from S₂→S₀ and S₁'→S₀, whereas 2^4- 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.