Theoretical Study On The Structures And Properties Of Organic Molecules Containing Nitrogen Heterocycles

Organic light-emitting diodes(OLEDs)have been widely used in many fields because of their special photoelectric functions.The choice of such diode materials is the key.Bicyclic heterocyclic compounds are becoming a research hot spot because of their rich photophysical properties.Based on the time-dependent functional density theory,ten kinds of organic molecules containing pyrazole ring and ten kinds of imidazole ring were selected to optimize the ground state structure of the molecules,and the electronic transition and spectral characteristics of different molecules were calculated and analyzed.In the corresponding solvent(SMD),calculate and fit the spectral characteristics of the molecules,so as to more specifically study the effects of different substituent on the overall structure and properties,and further screen out more suitable molecules as luminescent materials,which can provide a certain theoretical reference for the application of organic nitrogencontaining heterocyclic molecules and their derivatives in OLED materials.After fitting the UV absorption and fluorescence spectra of the molecules and studying their vertical excited state properties,it is found that in pyrazole based molecules,the polarity of pyrimidine pyrazole molecule is relatively low due to the high symmetry of the six membered ring,which makes the electron distribution more uniform,reduces the energy,and shifts the wavelength to the red direction,so the corrected peak wavelength of phosphorescence emission is 685 nm,just within the wavelength range of red light(625～740 nm).Compared with the fluorescence spectra,it is found that the pyridine pyrazole molecule with high symmetry has special spectral characteristics,which has the minimum Stokes shift and the longest phosphorescence emission wavelength,and may have relatively excellent red phosphorescence luminescence characteristics.In imidazolyl molecules,the molecule containing diphenylamine structure shows strong electron absorption under the combined action of diphenylamine induction and conjugation,resulting in obvious differences in structural parameters between this molecule and other molecules.The conjugation effect of molecules makes the distribution of electron cloud more uniform,reduces the polarity of the overall molecular structure,makes the molecules easy to transition,and can produce obvious shift,which can be used as a good red phosphorescent material.