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

Abstract

We report intense dopant-matrix afterglow systems with an afterglow efficiency (Φ_AG) of 47% and an afterglow lifetime (τ_AG) 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 <i>k</i>_nr + <i>k</i>_q 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 Φ_ISC and a small <i>k</i>_P to obtain a high Φ_AG and a long τ_AG. Besides, triplet-triplet annihilation has been found in the dopant-matrix system at high doping concentrations to further increase Φ_AG.