Recent progress on exciplex-based organic long-persistence luminescent materials
The field of pure organic long-persistence luminescent(LPL)materials has been experiencing a substantial surge of interest owing to its impressive characteristics.These materials offer several advantages,including flexible molecular structures and functionalities,ease of fabrication,freedom from noble metals,excellent biocompatibility,and broad application possibilities.Such attributes make them highly suitable for applications in data encryption,bioimaging,and secure printing,signifying a breakthrough in organic optoelectronics.Despite these advantages,LPL materials have several limitations,such as limited persistence duration,overall lifetime,reduced stability,and efficiency.These issues underscore the urgent need for more comprehensive and focused research on material development,stimulating the exploration of new design strategies to address the current limitations and enhance the performance and applicability of LPL materials.Efficient organic LPL materials can be achieved through strategic molecular design approaches.To enhance the intersystem crossing(ISC)process,various methods have been suggested,e.g.,the addition of heavy atoms,the reduction of the energy gap,hyperfine interaction,and the manipulation of heteroatoms.Creating a rigid environment prevents the nonradiative loss of triplet excitons.This common approach helps shield chromophores from oxygen quenching and minimizes molecular vibrations through H-aggregation,crystallization,host-guest systems,and polymerization.Furthermore,the presence of impurities in pure organic materials with LPL emission can considerably hinder their performance.However,a notable achievement in the field of LPL emission is the development of donor-acceptor exciplex materials.Exciplex-based LPL materials achieve luminescence through effective charge transfer between donor and acceptor molecules;under the excitation of an external light source,electrons transit from the highest occupied molecular orbital of the donor to the lowest unoccupied molecular orbital of the acceptor,thereby achieving electron transfer and separation.Thus,the donor and acceptor molecules form stable radical cations and anions,respectively.Subsequently,the radical anion formed by the acceptor slowly recombines with the radical cation of the donor,endowing the exciplex-based LPL materials with extended luminescence duration.Therefore,the interaction between donors and acceptors is crucial,as it influences the LPL time and efficiency.The ongoing investigation of donor-acceptor exciplex systems holds considerable potential for unlocking substantial advancements in LPL materials,thereby opening up new avenues for their application in cutting-edge technologies.This review explores the fundamental design principles of exciplex-based LPL materials,detailing the mechanisms and various exciplex systems.It emphasizes the critical role of donor-acceptor interactions in determining the LPL time and luminescence lifetime.Moreover,the relationship between the structural and LPL properties of these materials is summarized.Despite the promising prospect of exciplex-based LPL materials,several limitations need to be addressed,including short LPL duration,reduced efficiency,and compromised stability,along with challenges related to molecular design strategies and applications.Therefore,this review aims to offer researchers a comprehensive overview and assist newcomers in quickly understanding the importance of the evolving field of LPL materials.
organic long afterglowexcipient complexesdonor-acceptor molecular systemsduration
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