Twisted Phosphors that Violate Kasha's Exciton Model in Organic Systems

Kasha's exciton model proposes that T1 energy levels of organic compounds are insensitive to molecular aggregation and microenvironment change because of negligible small transition dipole moments of T1 states.This model holds true in most organic systems till now.Here we report the fabrication of twisted organic phosphors with intramolecular charge transfer characters and flexible molecular structures.When doped into different organic matrices,the twisted phosphor adopts different conformation,exhibits distinct phosphorescence colors and T1 energy levels,which violates Kasha's exciton model in organic system.Given that the change of phosphorescence colors and maxima can be readily distinguished by human eyes and conventional instrument,the twisted phosphors would be exploited as a new type of molecular probe,which would exhibit potential application in optical sensing and stimuli-responsive systems.

Advanced charge transfer technology for highly efficient and long-lived TADF-type organic afterglow with near-infrared light-excitable property

Heavy atom effects and n-π*transitions have been frequently reported to enhance room-temperature organic phosphorescence efficiency but lead to shortage of phosphorescence lifetimes.Unlike these reported studies,we conceive the incorporation of advanced charge transfer(CT)technology to boost room-temperature organic afterglow efficiency and simultaneously maintain afterglow lifetimes.Here we design difluoroboronβ-diketonate(BF2bdk)CT compounds with moderate singlet-triplet splitting energy(ΔEST)of around 0.4 e V,and relatively large spin-orbit coupling matrix elements(SOCME(S_(1)-T_(1)),1–10 cm^(-1))to achieve efficient intersystem crossing(ISC)and moderate rates of reverse intersystem crossing(kRISC,1–10 s^(-1)).The advanced CT technology,which includes multiple electron-donating groups and orthogonal donor-acceptor arrangement,have been found to narrowΔESTand enhance both ISC and RISC.Meanwhile,the organic matrices suppress nonradiative decay of BF2bdk’s T1states by their rigid microenvironment.Consequently,thermally activated delayed fluorescence(TADF)-type organic afterglow materials can be achieved with afterglow efficiency up to 83.0%,long lifetimes of 433 ms,excellent processablility,as well as advanced anti-counterfeiting and information encryption.Furthermore,with the aid of up-conversion materials and through radiative energy transfer,TADF-type afterglow materials with aqueous dispersity and near-infrared light-excitable property have been achieved,which paves the way for biomedical applications.

Cascade Synthesis of Luminescent Difluoroboron Diketonate Compounds for Room-Temperature Organic Afterglow Materials

Difluoroboronβ-diketonate(BF2bdk)compounds represent an important class of luminescent materials,whereas their synthesis requires multiple steps,which restrict their application in diverse fields.Here we report a cascade reaction to prepare BF2bdk from aromatic ketones,carboxylic acids,trifluoroacetic anhydride and boron trifluoride diethyl etherate.The cascade reaction is very simple and straightforward to produce BF2bdk with desired functional groups in reasonable isolation yields.Further,when some specific BF2bdk compounds are used as luminescent dopants,organic room-temperature phosphorescence with lifetimes>1.0 s and intense afterglow under ambient conditions can be achieved with the assistance by suitable organic matrices.The dopant-matrix materials exhibit excellent processability into desired patterns and large-area panels,and function as efficient donors of excited state energy transfer for the fabrication of red afterglow materials.