Blue Organic Long Persistent Luminescence: A UV/Violet-Light-Excitable and Green/Red-Light-Erasable Donor-Sensitizer-Acceptor Organic Afterglow System.

Abstract

We pioneered a donor-sensitizer-acceptor three-component system to devise organic long persistent luminescence (OLPL) materials, where the afterglow color is solely determined by sensitizer's emission color. Here we report two major breakthroughs in the field of OLPL: 1) tailored fabrication of pure-blue OLPL materials and 2) a direct observation of OLPL erased by green/red lights. We rationally designed blue thermally activated delayed fluorescence (TADF) sensitizers by connecting biphenyl-containing group with suitable HOMO and T1 energy levels to difluoroboron β-diketonate moiety based on the energy gap law and the El-Sayed rule. The resultant donor-sensitizer-acceptor three-component materials exhibit pure-blue hour-long OLPL afterglow with λOLPL < 450 nm; such pure-blue OLPL materials remain elusive in the reported studies. Mechanistic investigations confirm a unique charge-separation-induced OLPL pathway, involving electron transfer processes between donor, sensitizer, and acceptor. The OLPL materials are UV/visible-light-excitable. Remarkably, it is found that the OLPL emission can be erased by green or red light; the long-lived excited TADF sensitizers can be pushed by green/red lights to higher excited states, followed by fast nonradiative deactivation, enabling optical erasure. This unprecedented optical write-erase functionality, coupled with hour-long OLPL duration, would offer promising opportunities for rewritable photonic storage, encryption, and dynamic labeling applications.