Spectroscopic Insights Into DPA Upconversion in DNA/Ru(bpy) ₃ ²⁺ Hybrid Films

We report a mechanistic study of upconverted luminescence of 9,10‐diphenylanthracene (DPA) in a DNA/Ru(bpy) ₃ ²⁺ hybrid film, focusing on the spatial characteristics of upconversion and the role of mesoscopic aggregated structures. In our previous work, this hybrid system enabled low‐voltage electrochemiluminescence (ECL) with a response time of less than 100 μs through electrochemically triggered upconversion. However, the detailed mechanism, particularly the role of mesoscopic aggregated structures, has remained unclear. Here, by combining microstructural observation and spectroscopic analyses, we demonstrate that photoexcited upconverted luminescence of DPA occurs preferentially at aggregated regions of the DNA/Ru(bpy) ₃ ²⁺ hybrid film. Time‐resolved measurements show concentration‐dependent quenching of the Ru(bpy) ₃ ²⁺ excited state by DPA, consistent with triplet–triplet energy transfer (TTET) from Ru(bpy) ₃ ²⁺ to DPA followed by triplet–triplet annihilation upconversion (TTA‐UC). Furthermore, postwashing spectroscopic measurements indicate that DPA is preferentially retained in association with the aggregated regions. These observations support an important role of the mesoscopic aggregated structures in the TTET and TTA‐UC processes.