Electronic properties, such as HOMO and LUMO energies, band gaps, ionization potential （IP） and electron affinity （EA） of 2,7- and 3,6-1inked carbazole trimers, two conjugated oligomcrs with different linkages of ...Electronic properties, such as HOMO and LUMO energies, band gaps, ionization potential （IP） and electron affinity （EA） of 2,7- and 3,6-1inked carbazole trimers, two conjugated oligomcrs with different linkages of carbazole, were studicd by the density functional theory with Becke-Lee-Young-Parr composite exchange correlation functional （B3LYP）. The absorption spectra of these compounds were also investigated by time-dependent density functional theory （TD-DFT） with 6-3 IG＊ basis set. The calculated results indicated that the HOMO and LUMO of the 2,7- and 3,6-1inked carbazole trimers are both slightly destabilized on going from methyl substitution to sec-butyl substitution. Both IP and EA exhibit their good hole-transporting but poor electronaccepting ability. The presence of alkyl groups on the nitrogen atoms does not affect the intra-chain electronic delocalization along the molecular frame. Thus no significant effect on the band gap and absorption spectra of compounds has been found.展开更多
Quantum-chemical techniques were applied to investigate a series of conjugated polymers： poly（3-octylthien-2,5-ylene-co-pyrid-2,6-ylene） （pl）, poly[pyrid-2,6-ylenebis（3-octylthien-2,5-ylene）] （p2） and poly[py...Quantum-chemical techniques were applied to investigate a series of conjugated polymers： poly（3-octylthien-2,5-ylene-co-pyrid-2,6-ylene） （pl）, poly[pyrid-2,6-ylenebis（3-octylthien-2,5-ylene）] （p2） and poly[pyrid-2,5-ylenebis（3-octylthien-2,5-ylene）] （p3） comprising alternating n-excessive 3-alkylthiophene and n-deficient meta- or para-linked pyridine moieties. Their ground state and excited state structures were optimized with density functional theory B3LYP method, and the optical properties were calculated by the time-dependent density functional theory （TD-DFT） and ZINDO/S methods. Their HOMO-LUMO gaps （An-L）, the lowest excitation energies （Eex）, ionization potentials （IP） and electron affinities （EA） were obtained by extrapolating those of the polymers to the inverse chain length equal to zero （1/n=0）. The calculated results showed that the decrease of pyridylene content increased the HOMO level and decreased the LUMO level while the para-linkage further contributed to it. The IP are in the order： p1〉p2〉p3 but EA are： p1〈p2〈p3. In addition, the decrease of the pyridylene content and the para-linked pyridylene in the backbone of the polythiophene resulted in a narrowed energy gap and bathochromic absorption and emission peaks.展开更多
基金The project was supported by the Scientific Research Fund of Hunan Provincial Education Department (No. 05A002)the Prominent Mid-youth Science and Technology Foundation of Hunan Province (No. 04JJ1010)
文摘Electronic properties, such as HOMO and LUMO energies, band gaps, ionization potential （IP） and electron affinity （EA） of 2,7- and 3,6-1inked carbazole trimers, two conjugated oligomcrs with different linkages of carbazole, were studicd by the density functional theory with Becke-Lee-Young-Parr composite exchange correlation functional （B3LYP）. The absorption spectra of these compounds were also investigated by time-dependent density functional theory （TD-DFT） with 6-3 IG＊ basis set. The calculated results indicated that the HOMO and LUMO of the 2,7- and 3,6-1inked carbazole trimers are both slightly destabilized on going from methyl substitution to sec-butyl substitution. Both IP and EA exhibit their good hole-transporting but poor electronaccepting ability. The presence of alkyl groups on the nitrogen atoms does not affect the intra-chain electronic delocalization along the molecular frame. Thus no significant effect on the band gap and absorption spectra of compounds has been found.
基金Project supported by the Scientific Research Fund of Hunan Provincial Education Department （No. 05A002）, the National Natural Science Foundation of China （No. 50675185）.
文摘Quantum-chemical techniques were applied to investigate a series of conjugated polymers： poly（3-octylthien-2,5-ylene-co-pyrid-2,6-ylene） （pl）, poly[pyrid-2,6-ylenebis（3-octylthien-2,5-ylene）] （p2） and poly[pyrid-2,5-ylenebis（3-octylthien-2,5-ylene）] （p3） comprising alternating n-excessive 3-alkylthiophene and n-deficient meta- or para-linked pyridine moieties. Their ground state and excited state structures were optimized with density functional theory B3LYP method, and the optical properties were calculated by the time-dependent density functional theory （TD-DFT） and ZINDO/S methods. Their HOMO-LUMO gaps （An-L）, the lowest excitation energies （Eex）, ionization potentials （IP） and electron affinities （EA） were obtained by extrapolating those of the polymers to the inverse chain length equal to zero （1/n=0）. The calculated results showed that the decrease of pyridylene content increased the HOMO level and decreased the LUMO level while the para-linkage further contributed to it. The IP are in the order： p1〉p2〉p3 but EA are： p1〈p2〈p3. In addition, the decrease of the pyridylene content and the para-linked pyridylene in the backbone of the polythiophene resulted in a narrowed energy gap and bathochromic absorption and emission peaks.
