Photo‐induced Ultrafast Charge Transfer and Air‐Stable Radical Formation in Tetraphenylpyrene Derivatives

Stable organic radicals generated by photo‐excitation hold applications in molecular switching devices and information storage. It remains challenging to develop photo‐generated radical materials with rapid response and air stability in the solid state. Here, we report a structure based on 1,3,6,8‐tetraphenylpyrene derivative (Py‐TTAc) displaying photo‐induced radicals with air stability in the solid state. Photo‐induced electron transfer, exposed to a 365 nm ultraviolet lamp for 1 minute, affords radicals in Py‐TTAc powder as confirmed by electron paramagnetic resonance (EPR) spectroscopy. The maximum radical concentration reaches 2.21% after continuous irradiation for 1 hour and recurs more than 10 times without any chemical degradation. The mechanistic study according to the femtosecond transient absorption (fsTA) and X‐ray technology suggests that the radicals are derived from photo‐induced symmetry‐breaking charge separation (SB‐CS) and stabilized through non‐covalent interactions. The photo‐generated stable radical system is employed in anti‐counterfeiting paper and optoelectronic device applications. This study will provide insights into the development of photoactive organic radical materials.