Radiative and Nonradiative Recombinations in Organic Radical Emitters: The Effect of Guest–Host Interactions

Abstract

Radical‐carrying organic molecules have received significant attention to bypass the issue related to harvesting triplet excitons in current light‐emitting materials. While the computational efforts conducted so far have treated these radical emitters as isolated entities, in actual devices, they are embedded in a host matrix and subject to emitter–host interactions. Here, by combining molecular dynamics simulations and density functional theory calculations, the impact of the host matrix on the optoelectronic performance of radical emitters is evaluated, taking as a representative example the (4‐ncarbazolyl‐2,6‐dichlorophenyl)bis(2,4,6‐trichlorophenyl)‐methyl (TTM‐3NCz) radical emitter dispersed in a 4,4‐bis(carbazol‐9‐yl)biphenyl (CBP) host. A morphological analysis shows that steric effects around the radical centers, carried by the TTM electron‐poor moieties of the emitters, disfavor π–π interactions with the host molecules, which leads to random intermolecular orientations around the TTM moieties. The 3NCz electron‐rich moieties of the emitters, however, have much lesser spatial hindrance for intermolecular π–π stacking, which modulates the structural and electronic properties of the emitters in the host matrix. The influence of dynamic and static disorders on the radiative and nonradiative recombination processes is also investigated and it is found that the rates of nonradiative recombination are small, which opens the way to 100% internal quantum efficiency for the doublet‐based emission process.

Effect of Perturbative Vibronic Correction for Weak Fluorescence in Thermally Activated Delayed Fluorescence Systems

“…Also, the sum over the states should be terminated at some finite value of m max . Accordingly, the emission rate k p and the lifetime τ p can be calculated with the energy gap Δ E 01 and the effective TDM with the thermally averaged correction , …”

Organic Neutral Radical Emitters: Impact of Chemical Substitution and Electronic-State Hybridization on the Luminescence Properties

“…There is currently much interest in the exploration of stable organic neutral radicals for various applications including optoelectronics, spintronics, magnets, switches, or quantum information technologies. − Significant advances were very recently achieved in the field of radical emitters for electroluminescence. ,− It was found, for instance, that donor–acceptor (D–A • ) molecules, designed by attaching a carbazole or triarylamine (TAA) electron-rich donating group (D) to an electron-poor radical-carrying (A • ) tris­(2,4,6-trichlorophenyl)­methyl (TTM) or perchlorotriphenylmethyl (PTM) moiety, are stable and highly luminescent. ,, …”

Impact of chemical modifications on the luminescence properties of organic neutral radical emitters

“…[9][10][11][12][13][14][15] These radicals have an openshell electronic configuration and in many instances both the ground state (D 0 ) and the first-excited state (D 1 ) have a spin-doublet character. [16][17][18][19] This is in marked contrast with conventional closedshell organic emitters where the emissive singlet state is located above the first excited triplet state; as a result, B75% of the electrically generated excitons are triplet excitons whose emission is spin-restricted. In their majority, the neutral radical emitters that are currently investigated have a donor-acceptor (D-A ) chemical structure, in which an electron-poor acceptor radical (A ) core, such as a stable tris (2,4,6-trichlorophenyl)methyl (TTM) or perchlorotriphenylmethyl (PTM) radical, is covalently linked to an electron-rich donor group (D), such as a carbazole (Cz) derivative.…”