Synthesis And Optical Properties Of O-carborane Derivatives

As a kind of unique structure clusters compounds, carborane and its derivatives are of significant current interest with their three-dimensional aromatic, uniquely physical and chemical properties and highly chemically thermal stability, synthesis and theory research of their experiment emerged in endlessly. In this paper, we designed and synthesized a series carborane-based compounds, and research their optical properties. The research work was divided into two aspects: nonlinear optical properties and linear optical properties.In the field of nonlinear optics, the work was focus on the second order NLO properties. We designed and synthesis two kind of o-carborane with different conjugated chain:phenyl-ethyny and fluorenyl-ethyny to study the effect of conjugated chain on NLO. The HRS result shows that carborane-based compounds have large β values; the largest was 309*10-30 esu. Through the comparative study, we found that the introduction of carborane, increases the extention of conjugation and the change the structure can effectively improve NLO properties. Then we employed substituents with different substituent constant, the research suggests that the use of substituents can also effectively improve the NLO properties.In the field of linear optics the work was mainly focus on UV absorption and fluorescence emission(PL) properties, we design two groups of carborane carbazole derivatives: one-dimensional linear mono-substituted carborane and two-dimensional V shaped carbon-di-substituted carborane; thes compounds have different conjugated chain length. UV absorption and fluorescence emission spectra showed that the emission of these compounds was greatly influenced by solvents. These compounds have high fluorescence quantum yield in nonpolar solvents, and the maximum was 86%, being the highest among those emissive o-Cb derivatives in solution state. With the extension of the conjugated chain, UV absorption displays blue-shift but fluorescence emission spectra displays unsual blue-shift,the fluorescence quantum yield was also increased. To better understand the unusual properties in π-bridge elongated o-Cb dyads, time-dependent density-functional theory(TD-DFT) calculations were performed at the um06-2x/6-31G(d, p) level.The π-bridge elongation in mono-aryl dyads also lead to the unique hybrid of LE and CT emission and high PL efficiency. All these can be attributed to the unique electronic structure of o-Cb in the corresponding excited states, the contribution rate increases of transition lower than HOMO from to orbit lower than LUMO increased.The π-bridge elongation in the linear dyads leads to a unique hybrid excited state, LE and CT emission, and very high PL efficiency.The special fluorescence emission properties are cocktails of the local excited state(LE) and the charge transfer state(CT). The mono-carborane has higher fluorescence quantum yield and the DFT shows its local excited states dominated which radiate shorter wavelength emission. High PL efficiency and unique hybrid of LE and CT emission generated by π-bridge elongation made this kind compounds potential blue luminescence material.