Intense Organic Afterglow Enabled by Molecular Engineering in Dopant-Matrix Systems

We
report intense dopant-matrix afterglow systems with an afterglow efficiency (ΦAG) of 47% and an afterglow lifetime (τAG)
of 1.3 s. Luminescent difluoroboron β-diketonate (BF2bdk) dopants and their deuterated counterparts are designed with
naphthalene and carboxylic acid groups. After doping into benzoic
acid (BA) matrices, room-temperature afterglow brightness and afterglow
duration of the BF2bdk-BA materials have unexpectedly been
found to reach the levels of those at 77 K, which indicates that hydrogen
bonding between BF2bdk and BA, as well as the deuteration
technique, can reduce knr + kq of BF2bdk triplets to very small values even
at room temperature. Detailed studies reveal that the BF2bdk possesses typical 1ICT characters in the S1 state and distinct 3LE composition in the T1 state, and thus shows a high ΦISC and a small kP to obtain a high ΦAG and
a long τAG. Besides, triplet–triplet annihilation
has been found in the dopant-matrix system at high doping concentrations
to further increase ΦAG.