并苯纳米环[6]CA及其衍生物的电子结构和光物理性质的密度泛函理论研究

Theoretical study on the electronic structures and photophysical properties of carbon nanorings and their analogues

采用密度泛函理论PBE0方法在6-31G(d,p)基组水平上对比研究并六苯纳米环[6]CA及BN取代纳米环[6]CA-BN的几何结构及电子性质.同时探讨锂离子掺杂对不同体系的芳香性、前线分子轨道、电子吸收光谱及传输性质的影响.通过电离势、亲合势及重组能的计算,预测纳米环体系得失电子的能力及传输性能.结果表明:[6]CA的能隙很小,BN取代后,能隙明显增大;锂离子掺杂到两种纳米环中,在不明显改变前线分子轨道分布的前提下,几乎同步降低了最高占据轨道、最低未占据轨道能级,锂离子掺杂使载流子传输性能得到很大改善;电子吸收光谱拟合发现,BN取代使吸收光谱很大程度蓝移,吸收强度明显减小;而锂离子掺杂对光谱的强度及吸收范围没有明显影响.

Density functional theory （DFT） is used in a series of hexacene nanoring （[6]CA）, its boron nitride analogue （[6]CA-BN） and lithium ion doping derivatives to obtain an insight into electronic structure, aromaticity property, energy gap, ionization potential, electron affinity and reorganization energy. DFT calculations of these nanorings indicate that the energy gaps of the carbon nanorings are smaller than those of the boron nitride nanorings. The lithium ion doping will remarkably reduce the HOMO and LUMO energy. The aromaticities of the rings are investigated though nucleus-independent chemical shift （NICS） values. The NICS scan suggests that the aromaticities of carbon nanoring systems are more than those of boron nitride analogues, the aromaticities of boron nitride compounds are very weak due to orbital localization. We also calculate the reorganization energy to investigate the charge transport properties. The results show that the carbon nanoring and their analogues could serve as bipolar carrier transport materials in photoelectric functional materials, and the lithium ion doping significantly improves the charge transport properties. The [6]CA-BN nanorings serve as better electron-transport materials. Furthermore, the lithium ion doping significantly affects the charge transfer property of [6]CA-BN nanoring, making it used as bipolar carrier transport materials. The time dependant DFT investigations show that the boron nitride substitution leads to an important change in absorption spectrum with blue-shift. And lithium ion doping has no obvious influence on absorption spectrum.