Molecular Crystals and Liquid Crystals, Vol.444, 177-184, 2006
Ab initio study of substituted pyrenes for blue organic light-emitting diodes
Luminescence efficiency of pyrene molecule is very low because of the aggregation effect of planar pyrene molecules. However, 1,3,6,8-tetra-substituted pyrenes with large electron donating group were reported to give a bright blue fluorescence . In this paper, 1,6-bi-substituted and 1,4,6,9-tetra-substituted pyrenes as well as 1,3,6,8-tetra-substituted pyrenes were studied to find out the possibilities as the blue fluorescent materials of organic light-emitting diodes (OLEDs) . Geometrical and electrical calculations were performed by ab initio methods. HF/3-21G(d) basis set was used for the geometry optimization of the ground electronic states of those compounds. The geometry of the low-lying excited electronic state was optimized using configuration interaction with single excitation (CIS) method. The vertical and adiabatic transition energies were calculated by time-dependent density functional theory (TD-DFT) using the B1LYP functional with 6-31G(d) basis set. From calculational results, it was explained that the change in fluorescence wavelength was affected by the position and the number of substituents, through analyzing the change of energy levels of the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) of pyrene. Some of substituted pyrenes showed possibilities as stronger fluorescent materials. New efficient emitting materials for OLEDs were proposed from the calculation results obtained by tuning the position, the number of substitution and the species of substituting moiety.