TADF-Type Organic Afterglow

Manipulation of Organic Afterglow by Thermodynamic and Kinetic Control

The fabrication of room-temperature organic phosphorescence and afterglow materials, as well as the transformation of their photophysical properties, has emerged as an important topic in the research field of luminescent materials. Here, we report the establishment of energy landscapes in dopant-matrix organic afterglow systems where the aggregation states of luminescent dopants can be controlled by doping concentrations in the matrices and the methods of preparing the materials. Through manipulation by thermodynamic and kinetic control, dopant-matrix afterglow materials with different aggregation states and diverse afterglow properties can be obtained. The conversion from metastable aggregation state to thermodynamic stable aggregation state of the dopant-matrix afterglow materials to leads to the emergence of intriguing afterglow transformation behavior triggered by thermal and solvent annealing. The thermodynamically unfavorable reversible afterglow transformation process can also be achieved by coupling the dopant-matrix afterglow system to mechanical forces.

Modulating Tri-Mode Emission for Single-Component White Organic Afterglow

Achieving single-component white organic afterglow remains a great challenge owing to the difficulties in simultaneously supporting long-lived emissions from varied excited states of a molecule for complementary afterglow. Here, an extraordinary tri-mode emission from the radiative decays of singlet (S₁ ), triplet (T₁ ), and stabilized triplet (T₁ ^* ) excited states was proposed to afford white afterglow through modulating the singlet-triplet splitting energy (ΔE_ST ) and exciton trapping depth (E_TD ). Low-lying T₁ * for yellow afterglow was constructed by H-aggregation engineering with large E_TD and trace isomer doping, while high-lying T₁ and S₁ for blue afterglow with thermally activated emission feature were realized by reducing ΔE_ST through donor-acceptor molecular design. Therefore, the single-component white afterglow with high efficiency of 14.1 % and a lifetime of 0.61 s was achieved by rationally regulating the afterglow intensity ratios of complementary emissions from S₁ , T₁ , and T₁ *.

Boosting purely organic room-temperature phosphorescence performance through a host-guest strategy

The host-guest doping system has aroused great attention due to its promising advantage in stimulating bright and persistent room-temperature phosphorescence (RTP). Currently, exploration of the explicit structure-property relationship of bicomponent systems has encountered obstacles. In this work, two sets of heterocyclic isomers showing promising RTP emissions in the solid state were designed and synthesized. By encapsulating these phosphors into a robust phosphorus-containing host, several host-guest cocrystalline systems were further developed, achieving highly efficient RTP performance with a phosphorescence quantum efficiency (ϕ P) of ∼26% and lifetime (τ P) of ∼32 ms. Detailed photophysical characterization and molecular dynamics (MD) simulation were conducted to reveal the structure-property relationships in such bicomponent systems. It was verified that other than restricting the molecular configuration, the host matrix could also dilute the guest to avoid concentration quenching and provide an external heavy atom effect for the population of triplet excitons, thus boosting the RTP performance of the guest.

Unexpected long room-temperature phosphorescence lifetimes of up to 1.0 s observed in iodinated molecular systems

We investigate the heavy atom effect on difluoroboron(iii) β-diketonate (BF₂bdk) luminescent compounds. The iodine-substituted BF₂bdk powders with 38 wt% iodine substituents show insignificant afterglow at 77 K. Unexpectedly, when doped into phenyl benzoate matrices, the iodine-substituted BF₂bdk exhibits bright room-temperature phosphorescence with lifetimes of up to 1.0 s under ambient conditions.