Theoretical Investigation On The Nonlinear Optical Properties Of BN-doped Carbon Nanotube System

In recent years,nonlinear optical materials can play an important role in information storage,optical communication and even in the field of chemical and biological species detection.With the development of nanotechnology,the low dimensional nanomaterials（e.g.carbon nanotube,graphene etc.）get into the researcher’s view.Due to its special structure withπelectron conjugated and excellent stability,they are expected to be designed as new nonlinear optical materials.Based on the ab initio calculations,we took the carbon nanotubes（CNT）as a research object,to systematically study that the effects of introducing the triangular BN nanodot or its cooperation with the edge-modification via the electron-donating/withdrawing group on the NLO properties of CNT system.Specific contents of our work are as following:1.Firstly,we mainly investigated the NLO properties of the doped CNT systems with the triangular BN nanodot.The computed results reveal that introducing the triangular BN nanodot can be considered as a new strategy to effectively enhance the first hyperpolarizabilityβ₀ value of CNT system,and the doping of different types and sizes of domain have an important effect on theβ₀ value of the CNT system.Clearly,CNT-N₃B and CNT-B₆N₇ can exhibit the largestβ₀ value at the respective B-centered and N-centered series,the corresponding ofβ₀ value are 6.90×10⁴ and 1.47×10⁴ au,respectively.This is mainly due to the more N than B atoms in dopants,which can inject electron into the CNT system and exhibit the typical n-type characteristic.These results can be attributed to the realization of the effective charge transfer between the nanodot with neighboring C domains.2.Secondly,we took CNT-N₃B and CNT-B₆N₇ as theπ-bridge to explore the effect of doping BN nanodot or its cooperation with the edge-modification via the electron-donating/withdrawing group on the NLO properties of the hybrid CNT systems.The calculation results show that connect with the electron-donating/withdrawing NH₂/NO₂ groups for constructing the Donor-π-Acceptor framework can effectively improve the NLO properties of the doped CNT system,and modified position play an important role in theβ₀ value of the hybrid CNT system.In addition,all these edge-decorated CNT-N₃B structures,the edge-modification with the electron-withdrawing NO₂ group at the appropriate site can further enhance theβ₀ value of the hybrid CNT system due to the realization of the effective charge transfer between N₃B and C section,theβ₀ value of corresponding CNT-N₃B-NO₂（2）system 9.78×10⁴au is significantly higher than that of CNT-N₃B-NH₂（2）3.74×10⁴ au.For the CNT-B₆N₇systems,theβ₀ value(2.64×10⁴ au)of CNT-B₆N₇-NH₂（2）with the modified NH₂ group is significantly larger than the correlative CNT-B₆N₇-NO₂（2）(1.31×10⁴ au)system,which is mainly due to the electron transfer process can be strengthened by the edge-modification with the electron-donating NH₂ group.In conclusion,introducing the triangular BN nanodot or its cooperation with the edge-modification via the electron-donating/withdrawing group can be further enhance the first hyperpolarizability of CNT system,these appealing findings that can provide the innovative thinking and scientific theoretical guidance for the design of novel high-performance NLO materials based on CNT.