Theoretical Study On The Electronic Structures And Optical Properties Of Carbazole Boron And Diphenylphosphine Oxide Or Sulfide Complexes

As a new flat panel display technology, OLEDs have many merits such as: light weight,thin thickness, low cost, broad visual angle, fast response time, active emitting and highefficiency, and have received more and more attentions. The existing organicelectroluminescent （EL） materials of blue-emission face common problems in solid color,luminescence efficiency and service lifetime, etc. These problems stand in the way of theorganic light-emitting diodes （OLEDs） to be applied to the RGB panchromatic display. In thispaper, quantum chemistry calculations are performed for the in-depth investigation on thestructure and photoelectric properties for the experimental molecules and the newchemistry-modified molecules.First, a study of a new series of bipolar fluorophores that have been chemically modifiedfor use as highly efficient nondoped blue organic light-emitting diodes （OLEDs） has beencarried out based on existing molecular structures and a literature survey. The aim of thisstudy is to provide a profound interpretation of the optical and electronic properties and thestructure-property relationships of a series of new bipolar fluorophores. The study also aimsto predict the photophysical and optoelectronic properties of the new fluorophores. Thegeometry and the electronic structure of these molecules in the ground state were studied withDFT and ab initio HF, whereas the lowest singlet excited-state geometries were optimized byab initio singlet configuration interaction （CIS）. The absorption and emission spectra, both inthe gas phase and in THF, and the lowest singlet excited energies were calculated byemploying the time-dependent density functional theory （TDDFT） and the polarizablecontinuum model （PCM）. The results show that the optical and electronic properties （HOMOs,LUMOs, energy gaps, absorption and emission spectra, IPs, EAs and radiative lifetimes） ofthe potential fluorophore materials are all affected by differing π conjugations. In comparisonwith the calculated results of the newly emerged compounds in the gas phase, the absorptionand emission spectra with increasing oscillator strength are red-shifted in the THF solventphase, and the emission wavelengths in THF of all of the compounds are located in the blue todeep-blue range. The czflb compound exhibits similar optoelectronic properties to those ofczfub, indicating that a larger-sized fluorene core does not have a positive effect on theelectronic structure of entire molecule.Second, quantum chemistry calculations are adopted to investigate the optical andelectronical properties of ppocz, ppocz2and ppscz2, which are basically made up of twosegments: carbazole and （ph）₂P=O（S）. These three molecular materials are all experimentallypredicted well high-efficient blue phosphorescent organic light-emitting materials. Under thebasic of in-depth interpretation of the optical and electronic properties, we made slightlychemical modification under the known molecular back bones. We also predicted the opticaland electronical properties of the resulting molecule ppscz, and made some comparisons. Asshown by the results, it can be seen that the molecular geometry and electronic properties ofthe predicted material ppscz are similar with the known one ppocz. From the IPs, ppscz exhibits better hole-transporting property than ppocz. From the EAs, ppscz shows betterelectron-transporting property than ppocz2.