Improved and Controlled Singlet Oxygen Generation by Photoswitchable Organic Delayed Fluorescence Emitter

Abstract The construction of heavy atom or metal‐free pure organic systems that can simultaneously generate singlet oxygen (₁O₂) with enhanced efficiency via the Förster resonance energy transfer (FRET) process and have the ability to switch the ₁O₂ generation process with precise control is a challenging task. Herein, for the first time, we have designed and developed an all‐organic scaffold comprising of core substituted naphthalene diimide (cNDI) as a sensitizer, naphthalimide (NI) as an energy booster and dithienylethene (DTE) as a controlling unit with state‐of‐the‐art optical matching to obtain controlled and efficient ₁O₂ generation (yield Φ_Δ∼0.71) in toluene. The generated ₁O₂ was detected indirectly as well as directly (through phosphorescence of ₁O₂ at 1270 nm) and it has been used for the controlled photooxidation of various organic molecules. The developed molecule is capable of harvesting triplet by delayed fluorescence having an average long‐lived emission lifetime (τ ∼ 6.1 µs in solution and ∼ 30 µs in solid state) with a singlet‐triplet energy gap (ΔE_ST) of 0.1 eV. The steady‐state and time‐resolved emission spectroscopy (TRES) analyses at room temperature as well as at 77 K along with DFT calculations offered a detailed understanding of energy transfer (ET) pathways involved in controlled ₁O₂ generation.