Theoretical Investigations On The Optoelectronic Properties Of Organic Oligomer Complexes And Polymer

Recently, the scientific researchers endeavor to design and development new type of luminescent devices with high efficient, high stability, high brightness. Organic electronic light-emitting film technology also has many distinguished advantages, such as low power, easily bending, quick response, broad visual angle, large area display, full emitting color and so on, and they are compatible with many kinds of standard technology and can be made of low-cost light-emitting devices. So the polymers exhibit strong life in the aspect of planar color display. In this paper, calculations on the electronic ground state were carried out using density functional theory (DFT). The nature and the energy of singlet-singlet electronic transitions have been obtained by TD-DFT/B3LYP calculations performed on the optimized geometries. The excited geometries were optimized by ab initio CIS. Based on the excited geometries, the emission spectra are investigated. The theoretical study shows that by modification of chemical structures could greatly modulate and improve the electronic and optical properties of light-emitting materials and contribute to orientate the synthesis efforts and help understand the structure-properties relation of these conjugated materials. The following is the main results:1. The geometric and electronic structures of the oligomers in the ground state were investigated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited state of NPPP1 was optimized with ab initio CIS. To assign the absorption and emission peaks observed in the experiment, the absorption and emission spectra of the ground and lowest singlet excited states were calculated with time-dependent DFT (TD-DFT) and ZINDO. All DFT calculations were performed using the B3LYP functional and the6-31G basis set. The results show that the HOMO, LUMO, energy gaps, ionization potentials, and electron affinities for these polymers are affected by increasing the conjugated chain, which favors the hole and electron injection into OLED. The trend of the variation ofâ–³H-L and the lowest excitation energies with 1/n, and the electronic structure and optical properties of these polymers were extrapolated and analyzed. The absorption spectra exhibit red shifts to some extent [the absorption spectra: 359.47 (NPPP1) < 370.84 (NPPP2) < 373.84 (NPPP3) < 375.33 nm (NPPP4); 361.14 (NPPN1) < 370.34 (NPPN2) < 373.39 (NPPN3) < 374.62 nm (NPPN4)]. Our calculated spectra agree well with the experimental findings where available, showing small but systematic deviations.2. The geometric and electronic structures of the oligomers in the ground state were investigated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited states were optimized with ab initio CIS. To assign the absorption and emission peaks observed in the experiment, we computed the energies of the lowest singlet excited states with time-dependent DFT (TDDFT). All DFT calculations were performed using the B3LYP functional and the 6-31G basis set. The results show that the HOMOs, LUMOs, energies gaps, ionization potentials and electron affinities for each molecular are significantly affected by varying the aryl substituents, which favor the hole injection into OLEDs. The absorption and emission spectra exhibit red shifts to some extent [the absorption spectra: 335.85 (B1) < 370.63 (B1PPQ) < 376.77 (BtBPQ) < 388.67 (B2PPQ) < 412.93 nm (BNPPQ); the emission spectra: 391.48 (B1) < 430.11 (B1PPQ) < 435.86 (BtBPQ) < 444.57 (B2PPQ) < 463.28nm (BNPPQ)]. The radiative lifetimes (Ï„) of each oligomers are calculated as well. Because of introducing the cooperation with the electron donators such as the amidocyanogen in the common 4-phenyl-6-(4-phenylquinolin-6-yl)quinoline core for BNPPQ , which results in improving the hole-creating ability.