Design,Synthesis And Properties Of Dinuclear Cu(?) And Ag(?) Complexes

Over the past decades,organic light-emitting diode?OLED?technology has been used broadly in the fields of plane display,electronic equipment,lighting source and so on,and it has entered into many aspects of our life.As the third generation of TADF luminescent materials,following the fluorescent and phosphorescent materials,thermally activated delayed fluorescence?TADF?materials has been becoming the hotspot of research on the novel luminescent materials.Due to the characteristic smallness of the energy gap between the lowest singlet excited states?S₁?and the lowest triplet excited states?T₁?(?E_ST),the symmetrically prohibited intersystem crossing from T₁to S₁can be realized through thermal activation by the law of thermal dynamics.Therefore,the excitons generated by electricity in the OLED can be harvested reaching up to 100%by using TADF materials,which is comparable to phosphorescent materials with highly expensive metals.With the goal to achieve affordable and highly efficient TADF materials,nine emissive dinuclear ionic and neutral Cu???/Ag???compounds have been prepared by using 1,2,4,5-tetra?diphenylphosphonyl?benzene?tppb?as bridging ligand.Their luminescence properties have been studied in details:?1?By using 2-?1H-pyrazol-3-yl?pyridine?pypz?as terminally chelating diimide ligand and tppb as P^P bridging ligand,a binuclear ionic silver complex.[Ag₂?tppb??pypz?₂][NO₃]₂?1?was synthesized.This complex emits brightly green with the wavelength of its maximum emission at 506 nm,quantum yield of 42.3%.The?E_ST=0.09e V obtained from fitting its temperature-depended lifetime curve is close to the?E_STfrom the spectral tangent.The?E_STis small and the lifetime at the room temperature is short?5.7?s?,thus the complex is a good TADF luminescent material.?2?By using 2-?3-phenyl-1H-1,2,4-triazol-5-yl?pyridine?HPhtz?and2-methyl-6-?3-phenyl-1H-1,2,4-triazol-5-yl?pyridine?MePhtz?as terminal chelating N^N ligands and tppb as bridging P^P ligand,four neutral or ionic binuclear Cu???complexes,[Cu₂?HPhtz?₂?tppb?][BF₄]₂?2?,[Cu?HPhtz?]₂?tppb??3?,[Cu₂?MePhtz?₂?tppb?][BF₄]₂?4?,[Cu?MePhtz?]₂?tppb??5?.were synthesized.The complexes emit yellow light.Their spectra are broad and unstructured with obvious characteristics of charge transfer?CT?.Their maximum emission peaks are at 523-562 nm.Their quantum yields at the room temperature are 38.8%?2?,14.5%?3?,30.6%?4?,15.5%?5?,respectively.Their lifetimes are in the order or microsecond at room temperature.By fitting the lifetime-depended temperature curve,it is found that the values of?E_STare less than 0.3e V.The results of the studies of their emissive properties and computations indicate that these complexes diplay TADF at room temperature.?3?Byusing2-?1H-1,2,4-triazol-3-yl?pyridine?HPhtz?and2-methyl-6-?1H-1,2,4-triazol-3-yl?pyridine?MePhtz?as terminal chelating N^N ligands and tppb as bridging P^P ligand,four neutral or ionic binuclear Ag???complexes,[Ag₂?HPhtz?₂?tppb?][NO₃]₂?6?,[Ag?HPhtz?]₂?tppb??7?,[Ag₂?MePhtz?₂?tppb?][NO₃]₂?8?,[Ag?MePhtz?]₂?tppb??9?,were synthesized.The maximum emission wavelength of these complexes is between 488 and 519 nm,their light-emitting colors changing from blue to green.The complex[Ag₂?HPhtz?₂?tppb?][NO₃]₂?6?has a blue-shifted at low temperature,while the other complexes have a red-shifted at low temperature.?n addition,the quantum efficiency of the complexes of?6???7???8?are 72.3%,95.4%and 72.8%,respectively.From the study of temperature-depended lifetime,it is found that their lifetime changes from hundreds of microseconds or even thousands of microseconds at low temperature to a few microseconds or a dozen microseconds at room temperature.The temperature dependence of the luminescent properties for these complexes in solid state indicates that the emission of these complexes originates from two thermally equilibrated charge transfer?CT?excited states and exhibits highly efficient thermally activated delayed fluorescence?TADF?at ambient temperature.