Air-stable and visible-light-active p-type organic long-persistent-luminescence system by using organic photoredox catalyst

Organic long-persistent-luminescent (OLPL) materials that exhibit hour-long photoluminescence have advantages over inorganic materials, such as a sustainability, flexibility, and processability. The OLPL materials store the absorbed energy in an intermediate charge-separated state, but this charge-separated state is unstable to oxygen and does not exhibit persistent luminescence in air. The excitation wavelength of OLPL can be controlled by electron-donor and -acceptor materials, but previous materials require absorption mainly in the ultraviolet region. Here, we show OLPL systems that exhibit a persistent luminescence in air and can be excited by a wavelength from 300-nm to 600-nm. By using cationic photoredox catalysts as an electron-accepting dopant, stable charge-separated states are generated by the hole-diffusion process, as opposed to previous OLPL systems that depend on electron diffusion. By using a hole-diffusion mechanism and reducing the energy level of the lowest unoccupied molecular orbital, the OLPL system becomes stable in air and can be excited by visible light. The addition of hole-trapping material increases the LPL duration..