Synthesis And Properties Of Novel Naphthalimide Bipolar Fluorescent Materials

After decades of development,OLED technology has been widely used in display and lighting applications due to its wide viewing angle,high contrast display in bright light,wide temperature tolerance range,self-luminous,low energy consumption,high response speed and thin texture.Organic light-emitting materials as the core technology of OLED devices.Currently,great breakthroughs have been made.However,for the traditional light-emitting materials,due to the organic molecules can be in the thin film and solid state when there is aggregation-induced quenching（ACQ）effect.This has led to many undesirable properties of optoelectronic devices.Therefore,the design and preparation of excellent performance of light-emitting materials is particularly important.In this paper,naphthalimide derivatives are used as luminescent materials.Design and synthesis of bipolar molecules with distorted conformation by modification at the 9-and4-position of 1,8-naphthylimine.The aim is to synthesise compounds with aggregation-induced luminescence（AIE）/aggregation-induced enhanced luminescence（AIEE）properties,which result in enhanced luminescence in the solid or aggregated state.In this paper,six new naphthalimide derivatives were designed and successfully synthesised,and their optical,electrical and thermal stability properties were tested as follows:In the first system,the single naphthalimide derivative TPANI-TPA and the double naphthalimide derivative DTPANI-TPA were designed and synthesised.The main characteristic absorption bands of the compounds TPANI-TPA appeared at 307 nm and 427nm.The characteristic absorption peaks of DTPANI-TPA appeared at 311 nm and 430 nm.The emission peaks of both compounds in dichloromethane solution were 595 nm and 563 nm with CIE coordinates of（0.53,0.46）and（0.50,0.48）respectively.In the film state,the two emission peaks of TPANI-TPA and DTPANI-TPA were 555 nm and 562 nm,respectively,with CIE coordinates of（0.24,0.41）and（0.20,0.26）.In solid powder,the emission peaks of TPANI-TPA and DTPANI-TPA are at 582 nm and 583 nm respectively,both with CIE coordinates of（0.54,0.46）.It exhibits yellow light in both solid and solution.TPANI-TPA and DTPANI-TPA both have good thermal stability.The HOMO energy levels were-5.16 e V and-5.17 e V,and the LUMO energy levels were-2.87 e V and-2.99 e V.The electron cloud distributions of the two compounds were calculated quantitatively.The solid-state fluorescence quantum yields of TPANI-TPA and DTPANI-TPA were 17.14%and 1.98%,respectively,with excited state lifetimes of 5.91,5.16 ns.The PL studies of TPANI-TPA and DTPANI-TPA in the THF/H₂O solution system confirmed that the compounds have AIEE properties.The second system introduces tristyrene and tetrastyrene groups with AIE properties.The main characteristic absorption band of compound TNI-TPA appeared at 302,341 and 383nm.The main absorption peaks of compound TPENI-TPA appeared at 301,340 and 356 nm.Both compounds had two emission peaks in dichloromethane solution,at 483 nm,529 nm and469 nm,541 nm,respectively.Their CIE coordinates were（0.25,038）and（0.20,0.26）respectively.The two emission peaks of compounds TNI-TPA and TPENI-TPA are at 480 nm,528 nm and 467 nm,516 nm,respectively,in the film state.The CIE coordinates are（0.24,0.41）and（0.20,0.26）,respectively.In the solid powder,the two compound emission peaks were at 583 nm,618 nm and 593 nm,620 nm with CIE coordinates of（0.57,0.43）and（0.60,0.40）respectively.Both compounds exhibit blue-green light in solution and orange-yellow light in solid powder.TNI-TPA and TPENI-TPA exhibit good thermal stability.The HOMO energy levels are-5.19 e V and-5.16 e V,the LUMO energy levels are-2.59 e V and-2.55 e V,respectively.The excited state lifetimes of TNI-TPA and TPENI-TPA are 2.3 and 1.87 ns.The electron cloud distributions of both compounds were calculated quantitatively.The third system was designed and synthesized with phenothiazine as the core and the bipolar naphthalimide derivatives PTZNI-Cz and PTZNI-TPA with butterfly conformation.The main characteristic absorption bands of compound PTZNI-Cz appear at 263,295,340and 420 nm.The characteristic absorption peaks of compound PTZNI-TPA appeared at 259,304,322 and 422 nm.The emission peaks in dichloromethane solutions of both compounds were at 527 nm,530 nm,with CIE coordinates of（0.35,0.52）and（0.28,0.51）,respectively.In the solid film state,the PTZNI-Cz and PTZNI-TPA emission peaks are at 624 nm and 611nm with CIE coordinates of（0.61,0.39）and（0.58,0.42）,respectively.Typical red fluorescent materials were synthesised.The HOMO energy levels are-5.1 e V and-5.06 e V,and the LUMO energy levels are-2.9 e V and-2.89 e V.The excited state lifetimes of PTZNI-Cz and PTZNI-TPA are 3.81,2.25 ns,and the PLQY is 97.35%and 9.62%,respectively.The results indicate that the different 9-position substituents of the 1,8-naphthylimine have a significant effect on the fluorescence quantum yield and lifetime.The compounds show good stability and all have a thermal decomposition temperature greater than 400°C.The PL studies of PTZNI-Cz and PTZNI-TPA in the THF/n-hexane solution system confirmed that the compounds all have AIE properties.