High energy triplet-state manipulation via temperature-responsive twisted hetero-annulation systems

Precisely controlling excited-state transitions is vital for advanced technologies, particularly for sensitive, long-lived triplet states. Unlike traditional research focused on the lowest-energy excited triplet state (T₁), this work focuses on the high-energy triplet state (T_n), which presents significant challenges due to its short-lived and elusive nature. By implementing an annulation strategy to tailor the size, geometry, and electronic properties of the π-conjugated systems, we achieve precise control over two distinct T_n-mediated pathways, T_n → S₁ → S₀ and T_n → T₁ → S₀ transitions, using temperature as an external trigger. This approach enables temperature-modulated blue-to-red afterglow, characterized by an exceptionally high energy gap of up to 0.76 eV between the delayed fluorescence and phosphorescence. It offers an elegant solution to resolving the key challenge in T_n manipulation, providing a blueprint for developing next-generation responsive organic semiconductors with tailored excited-state behavior.