Long-Lived Luminescence Emitted from Imide Compounds Dispersed in Polymer Matrices after Continuous Ultraviolet Irradiation and its Relation to Oxygen Quenching

Long-lived room-temperature delayed phosphorescence, called prolonged irradiation-induced delayed luminescence (PIDL), was observed in air for three imide compounds (ICs) dispersed in polymethyl methacrylate under UV irradiation after an induction time of 1.60-6.78 min, whereas the ICs alone showed only fluorescence after a short period of UV irradiation. The PIDL emission continued as an afterglow for several seconds (0.36-1.30 s) after the irradiation was stopped. In the initial stage of irradiation, the ICs in the excited triplet state (T-1) generated via intersystem crossing were immediately quenched by ground state triplet molecular oxygen (O-3(2)), and the excited state energy of ICs was transferred by photosensitization to O-3(2), generating singlet oxygen (O-1(2)), causing a gradual depletion of the concentration of O-3(2) in the host matrix. When most of the O-3(2) adjacent to the ICs had been consumed, the ICs started to emit a PIDL. The induction time until the appearance of PIDL was linearly proportional to the O-3(2) concentration. Optical measurements and numerical simulations based on the Jablonski diagram support the PIDL generation mechanism and reveal the relationships between the rate constants and oxygen permeabilities of the host matrices.

Automated summary

Long-lived room-temperature delayed phosphorescence, known as prolonged irradiation-induced delayed luminescence (PIDL), was observed in air for three imide compounds (ICs) dispersed in polymethyl methacrylate under UV irradiation. The PIDL emission continued as an afterglow for several seconds after the irradiation ceased. The induction time of PIDL was linearly proportional to the concentration of ground state triplet molecular oxygen (O-3(2)).