Density Functional Theory Study On The Electronic Structure And The Photophysical Properties Of Nanorings

Since the discovery of carbon nanotubes in1991, carbon nanotubes have beenextensively studied both experimentally and theoretically. The aromatic systems andpotential utilities in materials science have captivated the interests of syntheticchemists, theoreticians, supramolecular chemists, and materials scientists. The majorobjective of the present study is to explore the electronic structure, energy, ionizationpotential, electron affinity and aromaticity property of carbon cyclic analogues andtheir BN analogues by using density functional theory (DFT) and time dependentdensity functional theory (TDDFT). It provides the theoretical basis for designing andsynthesizing new sensitizers for nano-electronic devices. The major works are asfollows:(1) DFT has been carried out on a series of carbon nanorings and their BNanalogues to obtain insights into the electronic structure, energy, ionization potential,electron affinity and aromaticity property. The results indicate that the energy gap ofall the carbon nanorings is smaller than the BN analogues. The NICS scan indicatesthat the aromaticity of carbon nanoring systems is stronger than that of BN analogues,the aromaticity of borazine compounds are very weak due to localization of orbital.The Egapcalculations show that the BN analogues have an increased in the frontierorbital band gap compare with the carbon nanorings, it can be concluded that all thecarbon cyclacene enjoy a higher conductivity, on the contrary, the BN analogues havehigh kinetic stability and low chemical reactivity. For the carbon nanorings, the VIPand VEA are smaller than borazine systems, and the values of VIP of all nanorings aremuch bigger than that of VEA. The aromatic behavior of carbon nanorings and theirBN analogues is analyzed in terms of NICS, the NICS calculation suggests that thearomaticity of the carbon nanorings are more than that of BN analogues.(2) To investigate the role of different HF exchange schemes in hybridfunctional and long-range-corrected functional, we utilized several “hybrid”density functionals such as BP86, B3LYP, PBE0, BH&HLYP, M06-2X andLong-range correction such as CAM-B3LYP and LC-PBE. It is found that as theHF-exchange increases the absorption spectrum have slightly red shifted. ThePBE0functional is better than other functionals. Furthermore, the absorptionspectra of six systems calculated by PBE0are discussed subsequently. The results indicated that the absorption spectra of the [n]CPP systems exhibits alternationwhen n changes between odd and even. Regardless of whether n is the odd or even,as the number of carbon nanorings increase, the absorption strength for the [n]CPPsystems increase with the size of rings. The same as [n]CPP system, the absorptionspectrum for the [n]CA systems exhibits alternation when n changes between oddand even. In the absorption spectra for the [n]CPA systems, as the number ofcarbon nanorings increase, the absorption strength for the [n]CPA systems increasewith the size of rings. Very interestingly, it was found that the BN system isdistinct from [n]CPP system, regardless of whether n is the odd or even. Theabsorption strength of all BN systems increases linearly with the size of rings.(3) DFT has been carried out on a series of hexacene nanoring ([6]CA), its boronnitride analogue ([6]CA-BN) and their lithium ion doping derivatives to obtaininsights into electronic structure, aromaticity property, energy gap, ionizationpotential, electron affinity and reorganization energy. DFT calculations of thesenanorings indicate that the energy gaps of the carbon nanorings are smaller than theboron nitride nanorings. Notely, lithium ion doping will remarkably decrease theHOMO and LUMO energy. The aromaticity of the rings has been investigationthough nucleus independent chemical shift (NICS) values. The NICS scan suggestthat the aromaticity of carbon nanoring systems is more than that of boron nitrideanalogues, the aromaticity of boron nitride compounds are very weak due to orbitallocalization. We also calculated the reorganization energy to investigate their chargetransport properties. The results show that the carbon nanoring and their analoguescould be as bipolar carrier transport materials in photoelectric functional materials, thelithium ion doping significantly improving the charge transport properties. The[6]CA-BN nanorings as a better electron-transport materials. Furthermore, the lithiumion doping significantly affects the charge transfer property of [6]CA-BN nanorings,make it tend to as bipolar carrier transport materials. The time dependant DFTinvestigations show that the boron nitride substitution leads to important change ofabsorption spectra with blue-shift. And there is no obvious influence on the absorptionspectrum when lithium ion doping.