Theoretical Study On The Narrow Band Luminescence Properties Of Organic Multiresonance Materials

Narrowband organic luminescent materials based on multiresonance(MR)effect can not only improve image quality of displays,but also improve the overall performance of traditional organic light-emitting diodes.They have received extensive attention from researchers.However,the current luminescence mechanism of MR materials is still unclear and the design strategies for the MR materials are very limited.Therefore,we study the factors affecting the full width at half maximum(FWHM)of the fluorescence spectrum at the molecular level from the perspective of theoretical calculations,revealing the relationship between the structure and luminescence properties of materials.putting forward ideas for the design and development of new narrowband material systems.The research content is as follows:(1)Since the narrowing factor of the MR molecular emission spectrum is unclear,theoretical calculations were investigated on the narrowband luminescence properties of MR molecules based on the fan-shaped expanded molecular structure.With the analyses of molecular geometry,frontier orbital energy levels,relaxation energy,vibration frequency,emission spectra and electronic localization functions,it was found that the there is a narrowing trend for the luminescence peak with the fan-shaped expansion of the molecular structure,which is mainly attributed to the changes in relaxation energy and short-range charge transfer characteristics.The MR effect of the boron and nitrogen atoms induces the localization of the HOMO and LUMO on different atoms and minimizes their bonding/antibonding character;the resulting non-bonding molecular orbitals minimize the vibrational relaxation in the materials,allowing the realization of an extremely sharp luminescence band.This work summarizes the regular of emission band changes with the fan-shaped expansion of molecular structure,clarifies the cause of band narrowing,and provides a basis for the narrowband molecular design.(2)In order to study the relationship between molecular structure and performance of MR molecules,the narrowband characteristics of four MR molecules with different arrangements have been theoretically studied.The geometric structure,molecular frontier orbit,transition density matrix and charge density difference were theoretically studied,and the differences in charge transfer properties between two different molecular structures were analyzed.It is found that electrons of the target-molecule are mainly transferred from the electron-donating N atom to other nearby atoms,forming short-range charge transfer.There are short-range CT and part of long-range CT in the transmolecules,so their emission spectra are relatively broad.The research results clarify the relationship between the structure of MR materials and the luminescence properties,and provide theoretical guidances for the design of narrowband molecules.(3)Since novel structures of MR molecules with narrowband properties are rare,a series of MR molecules were studied in this section,and their molecular geometry,frontier orbital energy levels,relaxation energy,vibration frequency,spectra,natural transition orbits,and electronic localization functions were studied theoretically,it is found that BN-centered and BS-centered architectures exhibitnarrow emission spectra.The research results expand the narrowband multiple resonance molecular structure system and provide a basis for the development of multiple resonance molecules.