Synthesis And Characterization Of Multifunctional Organic Luminescent Materials Based On 2,4,6-triphenyl-1,3,5-triazine And Carbazole Derivatives

Since the beginning of the 21st century,organic semiconductor materials have attracted widespread attention because of their excellent performance,especially the practical application of organic light emitting diodes(OLED)in flat panel displays and solid-state lighting.OLED has excellent characteristics such as low driving voltage,high luminous efficiency and fast response speed.According to the luminescence mechanism,organic light-emitting materials can be divided into fluorescent materials and phosphorescent materials.The third-generation OLED luminescent material of thermally activated delayed fluorescence(TADF)material can effectively use both singlet and triplet excitons for radiation transitions.The research and development of organic red and green materials have been quite mature,but organic blue materials still have great limitations due to their inherent wide energy gap,unbalanced carrier charge transportation,and their fluorescence quenching in solids.For this reason,we designed a series of molecules based on the fluorene,2,4,6-triphenyl-1,3,5-triazine and carbazole derivatives,and studied their thermal stability,photoluminescence quantum efficiency,electrochemical energy level,crystal structure,carrier mobility and OLED device performance.The first part of the work is mainly that the different pendant moieties are introduced into fluorene(F)framework to correlate their optoelectronic differences with chemical structures of DBF,BOPF,FTRZ and p TFTRZ.FTRZ and p TFTRZ solid powder show higher melting points of 186? and 122 ?.The highest occupied molecular orbit energy levels are-5.95 eV for F,-6.02 eV for DBF,-6.11 eV for BOPF and-6.23 eV for FTRZ,and the corresponding lowest unoccupied molecular orbits energy levels are-2.03 eV,-2.19 eV,-2.25 eV and-2.55 eV.Due to the electron-deficient 2,4,6-triphenyl-1,3,5-triazine,FTRZ showed significant emission redshift of 75 nm in solution,and the photoluminescence quantum efficiencies of FTRZ and p TFTRZ solid powder were decreased to less than 1%.The unique molecular skeleton of F without any shielding substituent was feasible to produce highly efficient and stable blue emitter.The single crystal of F is an orthorhombic system while those of DBF,BOPF and FTRZ are all monoclinic system.The surface roughness of film are 4.32 nm for BOPF,1.11 nm for FTRZ and 11.8 nm for p TFTRZ.The thin solid film of FTRZ showed the highest electron mobility,and the whole carrier mobilities are decreased in order of FTRZ,BOPF and p TFTRZ.In the second part,we use the classic Suzuki coupling reaction to synthesize five blue TADF luminophores,namely OTrPhCzBr?PTrPhCzBr?OTrPhCz?PTrPhCz and OSTrPhCz.The glass transition temperatures of OSTrPhCz?OTrPhCzBr?PTrPhCzBr?OTrPhCz and PTrPhCz under solid powder obtained through thermal analysis were 175 ??237 ??285 ??257 ? and 313 ?,and temperatures at 5%mass loss of solid powder were 349 ??370 ??471 ??342 ? and 479?.The photoluminescence wavelengths of OTrPhCzBr?PTrPhCzBr?OTrPhCz and PTrPhCz in toluene solution are 431 nm?471 nm?424 nm and 469 nm,respectively.In the mixed solvents of water and tetrahydrofuran with different volume ratios,it was found that the four compounds did not exhibit aggregation-induced luminescence.Based on the cyclic voltammetry curves,their HOMO energy levels and LUMO energy levels were caculated.The calculated energy band gaps are-3.06eV for OTrPhCz?-3.02 eV for OTrPhCzBr?-3.39 eV for PTrPhCz and-3.44 eV for PTrPhCzBr,indicating that they show the deep blue radiation we want.Obviously,when the electron-donating groups of 2,4,6-triphenyl-1,3,5-triazine are introduced at different positions,their band gap changes greatly.This is due to the conjugation effect in the molecule.From ortho-position to para-position substitution,the LUMO of the compound decreased significantly,resulting in an increase in band gap.By analyzing the photophysical properties of the compound OTrPhCz in solid state,we found that it has room temperature phosphorescence.In order to study the effect of the number of substituents on room temperature phosphorescence,another compound OSTrPhCz was synthesized.Through the analysis of their UV absorption,fluorescence emission spectra and single crystal,it is found that OTrPhCz is more distort in spatial configuration than OTrPhCz,and the intermolecular interaction is stronger.In the crystal and powder states,the phosphor emits brighter phosphors and longer phosphorescence lifetime,indicating that the compound is conducive to the stability of triplet excitons in the aggregated state,the phosphorescence is brighter,and the emission time is longer.The measured phosphorescence lifetime of compound OTrPhCz is 47.18 ms,and the phosphorescence lifetime of compound OSTrPhCz is 463.08 ms,which is the same as our prediction.The blue OLED with OTrPhCz as the guest doped at a concentration of 20%has a lower starting voltage of 4.2V,and the correspoinding current efficiency,luminous brightness and external quantum efficiency are 4.2 cd/A,10389 cd/m~2 and 2.64%with low efficiency roll-off.It shows excellent electroluminescence performance.Finally,we obtained polymer P1 by Suzuki coupling polymerization.Fluorescence emission spectroscopy analysis shows that the three monomers are well polymerized together;the measured thermal decomposition temperature and glass transition temperature are 459 ? and 147 ?,respectively,indicating that the polymer P1 has good thermal stability.Through the CV curve,the energy gap E_g=2.784 eV of the polymer P1 is calculated to be smaller than the monomer PTrPhCzBr,which is beneficial to the electronic transition.