Design And Applications Of Excited-state Intramolecular Proton Transfer Materials With Condensed-state Strong Emission

Excited-state Intramolecular Proton Transfer Materials with condensed-state strong emission have have attracted wide attention in the fields of physics,chemistry and biological science,due to their advantages of large Stokes shift,good photostability and low self-quenching.However,ESIPT-based materials generally tend to emit light in blue and green emissions.In this thesis,two kinds of orange and red-emitting ESIPT-based materials have been designed and synthesized.By extending theπ-conjugate structure of ESIPT,the emission color of ESIPT materials shows orange and red emission in the long wavelength region.These fluorpphores show excellent performance in the field of organic light-emitting diodes（OLED）and temperature sensing.The detailed research work is decribled as follows:（1）ESIPT red emitting materials HBT-BF₂ and orange emitting materials HBT-TPA have been designed and synthesized,and their molecular structures were characterized and confirmed.The basic photophysical properties of these two materials were studied by solvation effect,steady and transient fluorescence spectra as well as density functional theory calculations.It is found that both materials have obvious characteristics of hybrid local charge transfer excited state（HLCT）and condensed-state strong emission.In addition,its thermodynamic and electrochemical properties were studied.The two materials have good thermal stability.The highest occupied molecular orbital（HOMO）and lowest unoccupied molecular orbital（LUMO）energy levels of HBT-BF₂ are-5.91 e V and-2.99 e V respectively,and the HOMO and LUMO energy levels of HBT-TPA are-5.83 e V and-3.67 e V respectively.These works have laid the foundation for the later applications.（2）Red emitting HBT-BF₂ and orange emitting HBT-TPA were used in the emitting layer to prepare single-molecule red and orange OLEDs.By optimization of device structures,the red OLED based on HBT-BF₂ shows the maximum external quantum efficiency（EQE）of 2.0%.The device exhibitsefficient and stable red emission,with the fluorescence peak at 625 nm and the color coordinate being（0.6162,0.3813）.The HBT-TPA-based orange OLED shows a maximum EQE of2.0%,with an emission peak at 576 nm and a color coordinate of（0.496,0.4848）.The exciton utilization efficiencies in the two devices reached 43.2%and 33.8%,respectively,exceeding the maximum limit of 25%for traditional fluorescent OLED devices.This is due to the rapid high-level reverse intersystem crossing between the excited states of HLCT,which promotes the transformation of triplet excitons to singlet states in the process of electroluminescence.（3）Based on the red emissive material HBT-BF₂,the temperature sensing properties based on change of monomeric and ratiometric fluoresecence have both been studied.The fluorescence intensity of HBT-BF₂ in the organic solvent diethylene glycol dimethyl ether（MOE）decreases gradually with the increase of temperature.When it is used in temperature sensing,the maximum relative sensitivity（S_r）is 18.29%^oC^-1.Furthermore,the temperature sensing properties of the nanoparticles in water and phosphate（PBS）buffer was also studied.In order to overcome the disadvantage of detection fluctuation caused by single-wavelength fluorescence signal,a non-energy transfer ratiometric temperature sensor has been fabricated by doping HBT-BF₂ with a temperature-resistant triarylphosphate compound of C1.In the wide temperature range of 20-90^oC,the maximum S_r is 18.96%^oC^-1,and the temperature resolution is lower than 1^oC.Through the refinement study of reducing the temperature interval between the physiological temperature range30-50^oC,the maximum temperature sensing S_r achieves as high as 21.6%^oC^-1,with the maximum temperature resolution of 0.4^oC.More importantly,the temperature can be indicated simply by naked-eye fluorescence color change,which shows good potentials for robust and outdoor applications.