Manipulation of Triplet Excited States for Long‐Lived and Efficient Organic Afterglow

Abstract

In organic systems, it is very challenging to simultaneously achieve long afterglow lifetimes (τAG) and high afterglow efficiency (ΦAG). Here, luminescent dopants which feature a small rate of phosphorescence decay (kP) and modest rate of reverse intersystem crossing (kRISC) are designed and knr + kq values (nonradiative decay and quenching) of triplet excited states are suppressed by all means that include increasing molecular rigidity of luminescent dopants, screening organic matrices to strongly inhibit intramolecular motions of luminescent dopants, and deuteration of the luminescent dopants. Organic matrices are selected with large dipole moments to stabilize the singlet excited states of luminescent dopants via dipole–dipole interactions, reduce singlet–triplet splitting energy, and thus enhance ΦISC, leading to significant population of triplet excited states. Thermally activated delayed fluorescence mechanism is also used with modest kRISC to harvest triplet energies, significantly improve ΦAG to 64%, and maintain long τAG > 1.0 s. The obtained materials display intense afterglow brightness, excellent processability, and temperature‐sensing function.

Manipulation of Triplet Excited States in Two‐Component Systems for High‐Performance Organic Afterglow Materials

“…The non-monotonic change of τ PF with matrix's dipole moments suggest that MeOBP matrices can simultaneously decrease k F and enhance k ISC of spiroBF 2 S 1 states via dipole-dipole interactions and significantly enhance intersystem crossing of spiroBF 2 excited states. [75] SpiroBF 2 -MeOBP materials have been found to exhibit afterglow The photophysical data of spiroBF 2matrix-1 % samples show that, with the increasing of matrices' dipole moments, the S 1 levels of spiroBF 2 decrease while T 1 levels of spiroBF 2 show less change, which caused the decrease of ΔE ST . b) Schematic illustration of the long-lived and efficient organic afterglow system characteristic of small k P , modest k RISC and very small k q + k nr , as well as the design strategies of the spiroBF 2 -MeOBP afterglow system.…”

“…A reduced ΔE ST can facilitate intersystem crossing of ICT dopants; this is the reason why dipole-dipole interactions in dopantmatrix systems can enhance intersystem crossing. [54,[73][74][75][76][77][78][79] Zhang reported that, by doping a BF 2 bdk compound, 530, into tetralone matrices at 1.0 wt%, the obtained 530-tetralone-1 % materials showed afterglow efficiency of 26 % and lifetime of 0.4 s under ambient conditions. [73] Similar to tetralone matrices, benzophenone and their derivatives also possess large dipole moments.…”

“…When benzophenone (BP) was used as organic matrices, the spiroBF 2 -BP-1 % systems have been found to display intense afterglow upon ceasing excitation source, which possess afterglow quantum yields of 30 % and lifetimes of 0.6 s. [74] By fixing spiroBF 2 dopants and systematically varying the structures of organic matrices, it has been found that S 1 levels of spiroBF 2 decrease with the increase of dipole moments of organic matrices while T 1 levels of spiroBF 2 show less change with the dipole moments of organic matrices (Figure 7). [75] The reduced ΔE ST upon increasing the dipole moments of organic matrices can facilitate intersystem crossing of spiroBF 2 dopants. The prompt fluorescence lifetimes (τ PF ) of spiroBF 2 in BP, 4methylbenzophenone (MeBP), 4-ethoxybenzophenone (EtOBP) and 4-methoxybenzophenone (MeOBP) matrices have been found to increase with dipole moments from BP (1.11 ns) through MeBP (1.26 ns) to EtOBP (1.47 ns) first, and then slightly decrease with dipole moments from EtOBP (1.47 ns) to MeOBP (1.44 ns).…”

“…b) Schematic illustration of the long-lived and efficient organic afterglow system characteristic of small k P , modest k RISC and very small k q + k nr , as well as the design strategies of the spiroBF 2 -MeOBP afterglow system. Reproduced with permission from Ref [75]…”

Boosting organic afterglow efficiency via triplet–triplet annihilation and thermally-activated delayed fluorescence

“…S29, ESI†). The MeOBP matrices showed strong phosphorescence from 77 K to 240 K and thus largely interfered with the temperature-dependent phosphorescence measurements as reported in our recent study; 78 so benzophenone (BP) matrices were used in the place of MeOBP. At 77 K, the phosphorescence spectra of NPhRedBF 2 –benzophenone materials have been found to exhibit a structured emission band ranging from 630 nm to 850 nm with emission maxima at 658 nm (Fig.…”