Theoretical Study On Structures And Nonlinear Optical Properties Of Modified Borane/Carborane System

It has attracting more and more scientist attention to design and synthesis highperformance nonlinear optical（NLO） materials for their interesting photoelectric properties and potential applications. This work employed density functional theory（DFT） by designing the NLO molecules containing borane and carborane. Carboranes are a class of polyhedral boron cluster compounds containing two carbon atoms in the cluster cage; they exhibit threecenter two-electron bonds as well as three dimensionally conjugated electrons that confer high thermal and chemical stability. Also, hydrogen atom having substitution properties, this makes it active about this compound.The purpose of this paper is that:（1） to understand the electronic structues and properties of boranes and carboranes;（2） to explore rational DFT functions to calculate the NLO responses of boranes and carboranes;（3） to study the regularity of variation of the properties of the new NLO system design. The main contents following three aspects:1. The structure and NLO responses of nine molecules [M, N]（M, N are labeled as the number of thiophene rings on the left and right part, respectively） on the basis of thiophenefused benzocarborane were studied. Among them, three symmetric molecules [1, 1], [2, 2], [3, 3] have been synthesized by experiment, other six asymmetric molecules [1, 2], [1, 3], [1, 4], [1, 5], [2, 3], [2, 4] were designed by theory. The results show that when the number of thiophene rings M and N is equal, β_tot values increases with increasing the number of thiophene rings. Interestingly, when sum of M and N is constant, larger difference between M and N is, larger β_tot value is. Especially, [1, 3] with four thiophene rings has the largest β_tot value（3553 au） which is 54 times larger than 66 au of [2, 2] with four thiophene rings.2. Renctly, two thiophene-fused benzocarborane derivatives Tb1 and Tb2 were synthesized through experiment by Morisaki. The recently search has showed adding Li atom can improve NLO response, so, we adding Li atom in Tb1 and Tb2 to get Tb1-Li and Tb2-Li. The result show the valence electron lithium atoms are attracted to Tb1 and Tb2, besides, the transferred electron locates different region. Thus, adding one Li atom causes prominent variations in Δβ_tot of Tb1 and Tb2. The β_tot value of Tb1-Li is about 160 times larger than that of Tb1. However, β_tot value of Tb2-Li is only about 5 times larger than that of corresponding Tb2.3. In this part work, an unusual Li@B₁0H₁4 dimer with different spin multiplicities was theoretical designed: triplet（1）, open-shell singlet（2） and singlet（3） to explore the structure and the NLO responses properties. Firstly, three kinds of structures have great difference: two twist angle（The article in a specific representation of the dihedral angle） of Li@B₁0H₁4 are: 13.71o, 1.65o and 0o, respectively. As a result, the first hyperpolarizability（β_tot） value show interesting change trend: 1（19129） < 2（35992） < 3（77660 au）. Importantly, three different spin multiplicities of the first hyperpolarizability can explain the trend of first hyperpolarizability: 1（λ_max = 362） < 2（λ_max = 396） < 3（_λmax = 431 nm）, which apparent red shift with three spin multiplicities.We hope that our study not only can prove inspire on nonlinear optical properties based on borane in future. But also provide an important theoretical basis on NLO materials of borane and carborane system.