Organic Long Persistent Luminescence Through In Situ Generation of Cuprous(I) Ion Pairs in Ionic Solids

Recent development of most organic long persistent luminescence (OLPL) systems employed binary or tertiary doping. However, the design strategies towards OLPL materials with hour-long afterglow duration are still quite limited. Here, we propose a novel OLPL system through melt-casting method with 0.1 mol % of Cu^I complexes: 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl BINAP-CuX (X=Cl, Br and I) doped into the triphenylphosphine (TPP) host. The charge separation was initiated prior to excitation through host coordination with Cu^I complexes, resulting in semi-free halogen ions and in situ generated Cu^I cations, which forms TPP + BINAP-CuX ionic pairs and subsequently ionic solids. The OLPL lifetime can be readily modulated by different halogen atoms and the afterglow can last up to more than 3 hours perceivable to human eyes. This is a rare example of OLPL initiated through host-guest coordination that could potentially expand the definition of OLPL systems and design strategies.