Nonlinear Optical Properties of a Series of 6,12-Diethynylindeno[1,2-<em>b</em>]fluorene Derivatives

Abstract

The polarizabilities (αs) and second hyperpolarizabilities (γs) of a series of 6,12-diethynylindeno (1,2-b)fluorene derivatives were investigated by the density functional theory CAM-B3LYP method. The calculated results indicate that these molecules possess considerably large second hyperpolarizabilities. Replacing the 6,12-hydrogen atoms on indeno(1,2-b)fluorene molecules by ethynyl silyl or oxygen atoms results in a change in the geometry of the molecular structure, which affects the nonlinear optical (NLO) properties. Introducing ethynyl silyl groups into the molecules can increase the αs and γs values, while these values decrease introducing oxygen atoms into the molecules. Also, the γs values depend on the 2, 8-disubstituted R groups (R=H, F, CH3) of the indeno(1,2-b)fluorene molecules. When R is methyl, the molecule has much larger αs and γs values. Moreover, according to time-dependent density functional theory calculations on the indeno(1,2-b)fluorene series, the maximum absorption wavelength of the ethynyl silyl derivatives display a bathochromic shift due to increasing conjugation, while a blue shift of the maximum absorption wavelengths are observed in the oxygen-substituted derivatives because the conjugation decreases as the molecular structure is distorted.