Effective fluorescent turn-on detection of ionizing radiations through controllable intramolecular photoinduced electron transfer

In order to explore the detection of gamma radiation via intramolecular photoinduced electron transfer (PET) and the interaction between molecular structures and fluorescence enhancement, we conducted an in-depth study of the perylene tetracarboxylic diimide (PDI) series of fluorescent probes capable of detecting HCl in the non-polar CHCl₃ solutions. To simulate the interaction between ionizing radiation and fluorescent molecules, we used HCl titration method to predict the ability of PDI-n to detect gamma rays. The results show that the combination of PDI-n and HCl can enhance the fluorescence through retro-PET process. In addition, the fluorescence enhancement multiple gradually decreased with the enlargement of alkylamine side chains. In the direct irradiation experiment of ionizing radiation, PDI-n can also show a good fluoresence enhancement to gamma rays. Similar to the above HCl titration tests, the fluorescence increament stronthly depends on the alkylamine side chains lengths. The maximum fluorescence increament of PDI-1 is 22.24, and the fluorescence enhancement multiple of PDI-1–PDI-4 decreases when increasing the alkyl chain length. Besides, combining density functional theory (DFT), time-dependent density functional theory (TDDFT) calculations and electrochemical tests, the relative positions of each energy level obtained from the experiment indicate that the PDI-n molecule is beneficial to the occurrence of the intramolecular PET effect. Using femtosecond transient absorption spectroscopy (fs-TAS) and transient fluorescence spectroscopy (TFS) tests, the lifetime of charge separation was obtained, and the efficiency of the PET process was characterized by the rate constant. We found that fluorescent molecules with shorter side chains can realize PET more efficiently. Therefore, this work exploits the intramolecular PET mechanism for efficiently detecting gamma rays using a series of fluorescent probes, and reveals the law of the influence of molecular chain length on the PET effect. Which provides theoretical support for the development of new materials for effective and sensitive detection of ionizing radiation.