Design,Synthesis And Optoelectronic Properties Of Thermally Activated Delayed Fluorescence Materials Based On Fused Acridine Donors

Organic light emitting diode(OLED)has the advantages of flexible folding,high resolution and low power consumption,thus it has become the new frontier and growth point in the field of organic optoelectronics in the 21st century.As the most promising third-generation luminescent materials,thermally activated delayed fluorescence(TADF)materials can simultaneously utilize single and triplet exciton without using noble metals to achieve 100%internal quantum efficiency.In order to obtain highly efficient TADF materials,we designed and synthesized a series of pure organic TADF molecules based on fused 9,9-dimethyl-9,10-dihydroacridine(DMAC)and discussed their electrochemical,photophysical and electroluminescent properties.The results are listed as follows:1.A new electron donor namely TMQAC was designed and synthesized by fusing two DMAC moieties in parallel fashion.Two TMQAC-based TADF emitters featuring twin D-A structure with diphenylsulphone(DPS)and triazine(TRZ)as acceptors exhibited obvious TADF character and high PLQY.The OLED devices based on these emitters exhibited maximum external quantum efficiency(EQE_max)of 14.3%and 20.7%for DPS-TMQAC and TRZ-TMQAC,respectively.For comparison,to study the structure-property relationship of materials,another donor with an additional methyl group similar to TMQAC,namely Me TMQAC,was designed and used to construct two emitters,namely DPS-Me TMQAC and TRZ-Me TMQAC.It was found that the extra methyl substitution can significantly affect the molecular geometry and result in different optical properties.2.Inspired by the work of TMQAC,aiming to study the effect of molecular structure on the optical behavior of materials,a new donor namely PTMQAC was designed and synthesized by fusing two DMAC moieties in an N-para fashion.Two new emitters namely TRZ-PTMQAC and PM-PTMQAC were synthesized by linking PTMQAC with the acceptor triphenylpyrimidine(PM)or triphenyltriazine(TRZ).Both emitters exhibited small?E_ST and their emission maxima were greatly red shifted.However,they showed significantly lower PLQY.The OLED based on PM-PTMQAC acquired an EQE_max of 5.6%,revealing the great impact of ring fusing pattern on the device performances.3.Based on the work of TMQAC,to further study the effect of ring-fusing fashion on the material properties,a new twin-acridine donors was designed by fusing two DMAC moieties angularly,namely TMDBP.It was found that the two fused DMAC units presented dominant quasi-equatorial(QE)conformation because the great steric repulsion between the hydrogen atoms on methyl groups and N-H group.Two donor-acceptor type TADF emitters,namely TMDBP-PM and TMDBP-TRZ,were constructed by connecting TMDBP with acceptors of triphenylpyrimidine(PM)or triphenyltriazine(TRZ)via Buchwald-Hartwig C-N coupling reaction.Both emitters exhibited small?E_ST,obvious TADF character and high PLQY.The OLED device based on TMDBP-PM achieved a high EQE_max up to 24.2%,along with good roll-off performance at high brightness.4.Based on the work above,aiming to construct efficient red TADF emitters,two novel red TADF D-A type emitters namely NAI-TMDBP and NAI-TMQAC were constructed by connecting naphthalimide(NAI)acceptor with two efficient TADF donors,TMQAC and TMDBP,respectively.As expected,two novel red TADF D-A type emitters NAI-TMDBP and NAI-TMQAC were required.Because the suitable space steric hindrance and large rigid structure,the two molecules show small?E_ST less than 0.1 e V and obvious TADF character.The OLED device based on NAI-TMDBP achieved the best device performance with an EQE_max of 19.0%and a maximum emission of 610 nm,demonstrating a facile molecule design strategy of red TADF materials.