Theoretical Study On Carbazole Derivatives

In the past decade, organic electroluminescent materials have become a fascinating field in the world for their wide range of applications, such as industrial production, military affairs, and medical treatment, etc. Organic electroluminescent devices have such advantages as low-voltage driving, high luminosity, high efficiency, low cost and large-area color display which can be realized.Thus there has been great interest in investigating organic electroluminescent materials and devices.In this paper, a new A-π-D-π-A type compound, named 3, 6-Bisbenzothiazolyl-N-ethylcarbazole, containing two benzothiazole rings as two electron acceptors and one N-ethylcarbazole group as an electron donor was designed. The optimized geometry of the compound in the ground state and the first excited state, frontier molecular orbital, electronic affinity, energy gap, absorption and emission spectra were studied by B3LYP and ab initio CIS methods at 6-31G(d, p) level. The results show that the compound was an excellent optoelectronic material. The dual fluorescence phenomenon related to intramolecular charge transfer (ICT) of the compound was investigated using twisted intramolecular charge transfer (TICT) model as well. Solvent effects were also taken into account by using the polarized continuum model (PCM), the results indicate that the compound emits dual fluorescence in polar or non-polar solvents, and the peak values of dual fluorescence are independent of solvent polarity.In order to further understand charge injection and transport properties of 3,6-Bisbenzothiazolyl-N-Ethylcarbazole, adjust its emission spectra, from the point of view of the molecular design, we chose weak different electron-donating groups (-CH3,-OCH3,-N(CH3)2) or electron-withdrawing groups (-CN,-CF3,-NO2) to chemically modified.We systematically studied derivatives by B3LYP and ab initio CIS methods at 6-31G(d, p) level, respectively, and obtained the properties of the ground state and the lowest excited state conformations, HOMOs, LUMOs, energy gaps, ionization potentials, electronic affinities, reorganization energies, vibrational spectra, absorption and emission spectra. The calculated results showed that the charge injection and transport properties as well as absorption and emission maximums could be tuned by changing different substituent groups at the same position of their parent compounds and two derivatives (derivative 3 and derivative 9) substituted by cyano-groups might be as good candidates for electroluminescent applications as hole or electron transport materials with blue light emission. All these investigations will provide a theoretical basis for the molecular structure design of organic electroluminescent materials.