The DFT Study On Non-linear Optical Property Of Closo-Carborane Derivatives

Molecular materials with nonlinear optical (NLO) properties are currently attracting considerable attention because of their potential applications in telecommunications, optical swithing, optical limiting and information storage, and so on. The design of new molecular NLO materials with high-performance has been the subject of extensive theoretical and experimental investigations. The methods to enhance the first hyperpolarizability of molecules are great diverse. For example, the NLO properties of traditional organic NLO materials are improved through the increase of the conjugation path and the choice of donors/acceptors; For metal-ligand NLO materials, their NLO properties are improved through the introduction of the transition metals and ligands; Meanwhile, there are many other strategies, including the use of chiral compounds as well as open-shell systems. With the perfection of the quantum chemistry computational technology, the theory study of molecular materials NLO property is also developing. This may provide theoretical evidence for synthesizing high-performance NLO materials.Carboranes and metallaboranes with special electron structures and favorable chemical stability become a potential promising NLO materials. There has been a growing concern about NLO property of carborane derivatives. Recently, many co-workers investigated NLO properties of a series of carborane compounds. Allis and co-worker studied the NLO properties of the system with 12-vertex closed carborane as bridge group, the results indicated that the rigid cage structure of icosahedral carborane polyhedra is in favor of the first hyperpolarizability.This paper employed density functional theory(DFT), combined finite-field(FF) method to calculate the NLO properties of a series of metal substituted carborane compounds. The results as follw:(1) Density functional theory (DFT) B3LYP method based on the 6-31G(d) level was employed to calculate the third-order NLO properties of 14-vertex bis-substituted borane derivatives. The polarizability and and second-order hyperpolarizability were calculated by means of finite-field (FF) method. The results show that bonding styles of carbon and metal elements was different in 14-vertex bis-substituted carborane and metallaborane. Introduction of metal atoms effectively enhance the molecular nonlinear susceptibility. Metallaborane, which as compared with carborane corresponds to a less frontier molecular orbital energy gap, may exhibit semi-conductor even conductor property. Meanwhile, the effective core potential basis set was used for metal atoms of metallaboranes. It shows that metal atom with different basis-sets have little influence on the calculation results. (2) Density functional theory (DFT) BHandHLYP method was employed to study the second-order nonlinear optical properties of 12-vertex substituted carboranes. The results show carboranes with alkali-metal substituted have considerably large first hyperpolarizability (β) values which is 2~3 order of magnitude larger than that of unsubstituted carborane (14.5 a.u). For halogen and organic group substituted systems, however, theβvalues are only enhanced by one order of magnitude. A lower transition energy with a larger oscillator strength and a larger transition moment will lead to a larger second-order NLO response in alkali-metal carborane. Alkali-metal atom has major contribution to largeβvalues.