Theoretical Study On Conjugated Compounds Containing Heterocycle For Organic Luminescent Materials

In this paper, following three systems were systematically studied by the quantum chemistry methods:(1) triblock co-oligomers of n-type conjugated oligoquinoline and oligoquinoxaline with thiophene endgroups; (2) nitrogen-linked poly (2,7-carbazole)s; (3) alkyne-linked carbazole polymers.Firstly, the type conjugated oligoquinoline with thiophene endgroups, oligothiophene-b-oligoquinoline-b-oligothiophene triblock co-oligomers,6,6'-bis-(5-meth-ylthiophenyl-2-yl)-4-phenyl-quinoline (B1TPQ),6,6'-bis-(2,2-bithiophenyl-5-yl)-4-phenyl-quinoline (B2TPQ), and 6,6'-bis-(2,2',5',2"-terthiophenyl-5-yl)-4-phenylquinoline (B3TPQ) are new materimals for organic light-emitting diodes (OLEDs). This paper attempted to expose the rules of the electronic and spectroscopic properties for n-type triblock co-oligomers, the electronic structures and optical properties of compounds (BITPQX, B2TPQX and B3TPQX) which are similar to B1TPQ, B2TPQ and B3TPQ were studied in this paper. The electronic properties of the neutral molecules, the highest-occupied molecular orbital (HOMO), the lowest-unoccupied molecular orbital (LUMO), ionization potentials (Ip), electron affinities (Ea) and the maximum absorption were calculated using B3LYP density functional theory. The calculated absorption spectra data are 403 nm (B1TPQ)< 447 nm (B2TPQ)< 492 nm (B3TPQ) and 419 nm (B1TPQX)< 471 nm (B2TPQX)< 523 nm (B3TPQX), which exhibit red shifts to some extent. This may be resulted from the electron-with drawing strength or the chain length of the oligothiophene blocks.These calculations show that each oligomer is significantly affected by the chain length of the oligothiophene blocks.Secondly, new nitrogen-linked poly (2,7-carbazole)s P1 are new materimals for organic light-emitting diodes (OLEDs). This paper attempted to expose the rules of the electronic and spectroscopic properties for nitrogen-linked poly (2,7-carbazole)s, and two novel complexes (P2 and P3) were proposed and designed, which were similar to P1. In this article, the geometrical structures of ground was optimized by B3LYP/6-31G (d) methods. Furthermore, through exploring the energies of the highest-occupied molecular orbital (HOMO), the lowest-unoccupied molecular orbital (LUMO), ionization potentials, electron affinities, the variation of band gaps (Eg) and the maximum absorption of the polymers, the article makes a point of exploring the effects on the electronic and optical properties of the carbazole-based conjugated polymers with different substituents in the polymer backbone.At last, this paper studied poly [(3,6-di-tert-butyl-N-hexadecyl-1,8-carbazolylene) butadiynylene] (P4), butadiynylene-linked poly (3,6-carbazole) (P5), butadiynylene-linked poly (2,7-carbazole) (P6) through the theoretical measurements with Gaussian software. To investigate the relationship between structures and properties of these multifunctional electroluminescent materials, their geometrical structures of ground and excited-states were optimized by B3LYP/6-31G (d) and CIS/6-31G (d) methods, respectively. The lowest excitation energies (Egs), the maximum absorption and emission wavelengths of these polymers were calculated by time-dependent density functional theory methods (TD-DFT). The important parameters for luminescent materials were also predicated including the ionization potentials (Ips) and electron affinities (Eas). Through above calculations, it is evidenced that these polymers can be considered as candidates for excellent OLEDs with good hole-creating abilities and high blue-light emission.This paper analyzed and investigated theoretically the electronic and luminescent properties of a series of heterocyclic compounds from the results, we found that density functional theory and time dependent density functional theory can provide reasonable geometry and electronic properties. So we can use this theory to design new kind of luminescent compounds materials.