Study On The Design,Synthesis And Photoelectric Properties Of New Nitrogen-containing Pyrene-based Compounds

Pyrene is a classical polycyclic aromatic hydrocarbon with a large planar conjugated structure.Pyrene-based compounds have been paid attractive attention in organic photoelectric research due to its high fluorescence quantum efficiency,excellent carrier mobility and charge injection capability and high thermal stability.However,pyrene tends to form strong ?-? stacking,decreasing of fluorescence quantum yield and degrading of color purity.The molecular packing can be effectively suppressed by the introduction of bulky peripheral attachments in the suitable positions of pyrene core.At the same time,the behavior will widen the distance between the chromophores and weaken the intermolecular carrier transport ability,which will reduce the performance of the device to a certain extent.So it should comprehensively consider the solid-state light-emitting efficiency and carrier transport capacity in the design and synthesis of new pyrene-based materials.In the paper,we synthesized series of efficient nitrogen-containing pyrene-based materials based on pyrene unit and nitrogen-containing groups with excellent carrier migration ability,and then studied the phototelectric properties of these compounds.The main research work includes the following contents:1.Eleven pyrenyl-based triarylamines were designed and synthesized and the photoelectric properties of these compounds were studied.Firstly,the propeller-shaped dipyrenyl-based triarylamines 2PyH,2PyMe,2PyOMe,2PyF and 2PyNO₂ with different substituents and tripyrenyl-based triarylamine 3Py were designed and synthesized.These compounds have high HOMO levels and good hole-transport abilities.Furthermore,the twisty propeller-shaped configuration can suppress the intermolecular force to some extent.The different substituents in the molecule have some influence on the photoelectric properties and intermolecular forces of these materials,which make the?37?Fs of the compounds vary greatly from 3.47% to 30.04%.Solution processed double-layer OLEDs using two representative compounds 2PyOMe and 2PyF as non-doped emitting layer were fabricated.The device based on compound 2PyOMe shows the best device performance with a turn-on voltage of 2.8 V,a maximum brightness?Lmax?of 4713 cd/m² and amaximum luminance efficiency?CE?of 5.41 cd/A.In general,the series of pyrenyl-based compounds has excellent carrier transport properties,but the solid-state luminous efficiencies of the compounds are not high by changing different substituents,indicating that the propeller-shaped configuration cannot efficiently inhibit the intermolecular forces.Secondly,in order to retain the triarylamine configuration and further improve solid-state luminance efficiency,a series of centrosymmetric 1,3-disubstituted pyrene-based triarylamines Py1–Py5 with pyrenylamine,fluorenamine,tetraphenyl ethylene amine substituents were designed and synthesized.These compounds have excellent fluorescence properties and their?37?Fs range from 33.4%–55.6%.All these compounds are also thermally and morphologically stable,showing high Td?330–455 ??and Tg values?109–258 ??.The compounds Py5 with tetraphenylethylene groups exhibit special aggregation-induced effect.Double layer solution-processed OLED devices were fabricated to investigate the light-emitting properties of the compounds Py1,Py3 and Py4.One of the devices using Py3 as emitter shows a best performance with Lmax of 6272 cd/m² and CE of 3.64%.2.Eight 1,3,6,8-tetrasubstituted pyrene-based compounds were designed and synthesized and the photoelectric properties of these compounds were studied.Firstly,a series of symmetrical dipolar configurational?SyPyH and SyPyMe?and asymmetrical X-shaped?AsyPyH and AsyPyMe?1,3,6,8-tetrasubstituted pyrene-based compounds with phenyl and diphenylamine groups were designed and synthesized.By studying the photoelectric properties of these compounds,the following relationship between structure and properties can be obtained.Compounds SyPyH and SyPyMe with dipolar configuration exhibit higher absolute?37?Fs than those of asymmetrical AsyPyH and AsyPyMe in dichloromethane and as drop-coating films,which reveals the dipolar structure can be beneficial for improving the PL properties of the compounds.Based on the DSC and XRD analysis,the compounds SyPyH and SyPyMe can form morphologically stable amorphous thin films with Tg values of 146 ? and 149 ?,respectively.However,there are no obvious Tg observed in compounds AsyPyH and AsyPyMe and the two compounds cannot form amorphous thin films.Furthermore,the solubilities of these compounds with bipolar configuration are excellent,however,the solubilities of these compounds with X-shaped structure are very poor,increasing the synthesis and purification of the new compounds.In all,the dipolar configuration has advantages over X-shaped in improving material properties.Two layer OLEDs featuring compounds SyPyH and SyPyMe as non-doped emitters show promising device performance with low turn-on voltage?2.9 V?,Lmax,CE,PE of 7359 cd/m² and 6683 cd/m²,3.66 cd/A and 3.79 cd/A,2.61 lm/W and 2.60 lm/W,respectively.OLEDs using compounds SyPyH and SyPyMe as doped emission layer show more excellent device performance with low turn-on voltage?3.0 V?,Lmax around 15100 cd/m² and 16100 cd/m²,CE of 12.4 cd/A and 13.6 cd/A and PE of 5.34% and 5.63%,respectively.Secondly,since there are many advantages of the dipolar 1,3,6,8-tetrasubstituted pyrene-based derivatives,we further modified the pyrene based on the configuration.Thus,a series of dipolar solution-processed 1,3,6,8-tetrasubstituted pyrene-based compounds?Sy Py1–SyPy4?with two 4-tert-butylphenyl segments at 1,8-positions and two hole-transporting triphenylamine or carbazole attachments at 3,6-sites of pyrene core were designed and synthesized.The introductionof 4-tert-butylphenyl groups into the 1,8-positions of pyrene ring can be beneficial to the solution-processed property of the materials.There is a benzene ring between the nitrogen atom in hole-transporting unit and pyrene core,widening the distance of the molecules,which can effectively suppress the intermolecular ?-? interactions and consequently leads to relatively high absolute?37?F up to 73.87%.These compounds exhibit high thermal stability and can form morphologically stable amorphous thin films with Td and Tg up to 539 ?and 189 ?,respectively.Solution-processed non-doped OLEDs using compounds SyPy2 and SyPy3 as emitters show promising performance with Lmax,CE,PE of 8741 cd/m² and 3550 cd/m²,4.03 cd/A and 2.41 cd/A,2.89 lm/W and 1.34 lm/W,respectively.3.A series of dipolar 1,3,6,8-tetrasubstituted pyrene-based blue compounds PyBm1,PyBm²,mPyBm1 and m PyBm² were designed and synthesized with two 4-tert-butylphenyl segments at 1,8-positions and two electron-transporting N-phenylbenzimidazole moieties at 3,6-sites of the pyrene core.Adding a benzene ring between the pyrene ring and the N-phenylbenzimidazole unit can increase the distance between the molecules and better inhibit the intermolecular stacking,which consequently leads to high absolute?37?Fs both in solution and film state with the values up to 100% and 86.78%,respectively.Furthermore,the introduction of benzimidazole moieties can efficiently enhance the electron-transporting properties of the compounds,which can improve the performance of devices.In addition,the benzimidazole moieties attached on the pyrene ring via para-and meta-linking modes and changing the molecular linkage from para-to meta-mode can tune the emission and obtain blue emitters with higher absolute?37?F,which demonstrates that the meta-linked architecture can more effectively reduce the ?-conjugation,twist the molecule and suppress the intermolecular ?-? interactions.All these compounds exhibit high thermal stability and can form morphologically stable amorphous thin films with Td ranging from 506–521 ? and Tg in the range of 182–215 ?.Two types of non-doped OLED devices were fabricated to investigate the light-emitting and electron-transporting properties of these compounds and the devices exhibit sky-blue or blue emission with promising device performance.Even without the electro-transporting layer,the OLEDs based on these compounds still exhibit nice performance,which indicates that the pyrene-based benzimidazole compounds have good electro-transporting property.One of the devices using meta-linked compound mPyBm² as emitting and electron-transporting layers shows a low turn-on voltage?3.6 V?,high current and power efficiencies?2.70 cd A–1,1.97 lm W–1?,Lmax around 9996 cd/m² as well as pure blue color purity?0.16,0.10?.4.In order to improve the hole-and electro-transporting properties of the materials,a series of dipolar 1,3,6,8-tetrasubstituted pyrene-based derivatives?PyTPA,PyCa Z and Py3CaZ?with a D-?-A configuration were designed and successfully synthesized.The specific synthetic strategy is introducing electro-withdrawing benzimidazole group and electro-donating nitrogen-containing unit into the 1,8-and 3,6-position of the pyrene core,respectively.The planar pyrene twists by the substituents,which can effectively suppress the intermolecular ?-? interactions of the molecules.All the three compounds exhibit high absolute?37?Fs both in dichloromethane?88.84–91.69%?and film states?75.67–83.35%?.All these compounds are also thermally and morphologically stable,showing high Td?520–523 ??and Tg values?200–223 ??.Two layers of solution-processed OLEDs using the designed compounds as emitting and hole-transporting layer were fabricated and they exhibit good device performance.The device based on PyCaZ not noly emit blue emission with the CIE coordinate of?0.20,0.15?,but also show the best performance with the Lmax,CE and PE of 5635 cd/m²,2.13 cd A–1 and 1.00 lm W–1,respectively.Even without the hole-and electro-transporting layer,the single layer OLEDs featuring Py3 CaZ as emitter still exhibit a promising performance with the Lmax,CE and PE of 4312 cd/m²,1.46 cd A–1 and 0.82 lm W–1,respectively,indicating the compounds have excellent hole-and electro-transporting abilities.