Novel Near-Infrared Organic Emissive Aggregates And Their Electroluminescent Diodes

Near-infrared pure organic emitting materials and their organic light-emitting diodes(NIR-OLEDs)have great potentials in the applications of information security display,optical communications,bio-imaging,etc.However,due to the energy-gap law,the bathochromic shift of the wavelength will induce exponential growth of the non-radiative decay rate,leading to a low emitting efficiency of the pure organic emitting materials.Meanwhile,OLEDs based on conventional materials are limited by the spin statics,in which only the 25%singlet excitons can be used,leading to a low external quantum efficiency(EQE).How to rationally design the high-efficiency pure organic NIR emitting materials?Is it possible to develop high-efficient NIR-OLEDs by breaking the spin statics?These are very challenging problems in the development of pure organic emitting materials.In this work,three pure organic emitting materials based on the acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile acceptor and triphenylamine donor were designed and synthesized.In solid states,these molecules can form intermolecular charge transfer aggregates.The molecular structure,packing modes in single crystals and their characteristics were compared to study their relationships.Moreover,these materials were finally used in OLEDs.The main contents are as follows:1.Based on the acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile acceptor,two novel pure organic emitting materials were designed and synthesized.With the formation of intermolecular charge transfer aggregates in films,highly-efficient NIR I emission were achieved and the thermally activated delayed fluorescence(TADF)were informed.Based on these dyes,the emission peak wavelength of the OLEDs are 682 nm、788 nm、804 nm,and the maxmum EQEs are 21.65%、2.42%、1.41%,respectively,which are highest EQEs among the TADF-OLEDs with similar electroluminescent wavelength.2.Based on the acenaphtho[1,2-b]pyrazino[2,3-e]pyrazine-9,10-dicarbonitrile acceptor,a novel pure organic emitting materials were designed and synthesized.With the formation of intermolecular charge transfer aggregates in films,the emission peak wavelength of the OLED is 1010 nm,which is the first TADF-OLED in NIR Ⅱ.3.The formation of intermolecular charge transfer aggregates in solid states was proved with experiments and theoretical calculations.The formation of intermolecular charge transfer aggregates can achieve significant red-shifted wavelength,inform and enhance the TADF characters from non-TADF molecule,as well as reduce the non-radiative decay,which demonstrate a new design strategy to achieve high-efficient NIR emission.