Preparation And Photoelectric Properties Of Triazine Nanostructured Aromatic Hydrocarbon TADF Materials

As a kind of nano-scale cyclic compounds,"Nano Grid-Aromatics"is a kind of closed non-conjugated molecule with multi-dimensional expansibility and unique stability.Because of its large volume,it can reduce intramolecular rotation and non-radiation transition.In addition,the lattice aromatic hydrocarbon material has a large molecular weight and molecular length,which is beneficial to the molecular orientation arrangement in the film state.Similarly,thermally activated delayed fluorescent materials,as the third-generation organic luminescent materials,have attracted extensive attention.However,the blue OLED based on TADF will have significant efficiency roll-off and short device life under high current density,there is still little research on delayed fluorescence of"aromatic hydrocarbons"at present.In this paper,different heterocyclic aromatic molecules were prepared by efficient Friedel-Crafts reaction,and the delayed fluorescence of"heterocyclic aromatic"molecules was realized.The prepared undoped solution-processed OLED devices also showed good performance.Firstly,cis-missing lattice was obtained by Friedel-Crafts reaction,and three aromatic hydrocarbons,DCz FGMe Trz,D2Cz FGMe Trz and D2Cz FGMe Trz,were successfully synthesized by nucleophilic substitution of aromatic hydrocarbons without catalyst and Ullmann reaction.It is found that all three materials emit blue light.At the same time,it is found by atomic force microscope that the introduction of long alkyl chains can obviously improve the film-forming properties of the materials.All three materials have good thermal stability and electrochemical stability,and their thermal decomposition temperatures are over 380℃.After systematic study of the UV-PL spectra of the three compounds,it was found that they all exhibited significant ICT effects which were beneficial to achieve TADF emission and all emitted blue light.We fabricated non-doped solution processed OLED devices for the three compounds,among which DCz FG2Me Trz had a maximum luminance of 4459 cd/m² and a maximum external quantum efficiency of 6.41%.Controlling theπ-conjugated length of the donor and acceptor can affect the energy transfer between them,which results in adjusting the distribution and energy level of the excitons,leading to TADF emission.Therefore,we considered increasing theπ-conjugated length of the triphenylamine unit to construct new triphenylamines and synthesized two new derivatives,DCz Ph G2Me Trz and DCz Ph FG2Me Trz.Both of them showed good film-forming properties and thermal stability,with a decomposition temperature over 400℃.After UV-PL spectroscopy testing,it was found that all the compounds exhibited significant ICT effects which were conducive to achieving TADF emission.Moreover,the emission of DCz Ph G2Me Trz had a blue shift compared with that of DCz Ph FG2Me Trz.We then fabricated non-doped solution processed OLED devices for both compounds,and they both emitted blue light.The maximum luminance of DCz Ph FG2Me Trz was5228 cd/m² with a maximum external quantum efficiency of 6.38%.Finally,we used stronger electron donor group and dimethyl triazine to form D-A structure,and successfully prepared DMACPh FGTrz and DMACPh GTrz Both of them have good thermochemical stability,excellent film-forming property and smallΔE_ST.Similarly,they also showed significant ICT effects that were conducive to achieving TADF emission.Through the fluorescence lifetime decay curve of the thin films,bi-exponential decay could be clearly observed for both compounds.Their delayed lifetimes were 1.4μs and 1.6μs,respectively,which proves the delayed fluorescence characteristics of"aromatic hydrocarbon"luminescent materials.Then,by preparing the undoped solution-processed OLED devices,it can be found that they emit green light and yellow light respectively,and they have good electroluminescent stability,with the maximum brightness of 6000 cd/cm² and the maximum external quantum efficiency of 10.25%.