Octupolar Films with Large Second Harmonic Generation and Electro‐Optical Effects

Abstract

Thin films that benefit from efficient octupolar molecular packing are prepared for second harmonic generation (SHG) and electro-optic (EO) applications. The films are composed of 1,3,5-tricyano-2, 4,6-tris(p-diethylaminostyryl)benzene (TTB) in a ploymethylmetacrylate (PMMA) matrix on aluminum/BK7 glass (Al/BK7) and polyimide/indium tin oxide (PI/ITO) substrates. Octupolar films prepared on both substrates display polycrystalline and cylindrical domains. The molecular orientation, SHG efficiencies, and EO coefficients of the crystalline domains are measured. In the cylinders, the molecular crystal planes are oriented perpendicularly to the major cylinder axis, whereas in the polycrystals, the planes are randomly oriented. While both structures exhibit high and stable SHG and EO efficiencies, the cylinders, in particular, exhibited a very large SHG, a large EO coefficient, and high thermal stability; these characteristics will be useful in second order nonlinear optical applications.

Theoretical Studies on Two-Dimensional Nonlinear Optical Chromophores with Pyrazinyl Cores and Organic or Ruthenium(II) Ammine Electron Donors

“…The β response is a third-rank tensor with multiple components, but the most heavily studied chromophores such as the DAS + cation show a largely 1D response dominated by the β zzz component, where the z direction is the long molecular axis. In addition to simple 1D dipoles, multidimensional species like 2D dipoles − and 2D or 3D octupoles − are of major interest. Such chromophores can offer significant advantages over 1D species, including larger NLO responses without the typical but undesirable accompanying decreased visible transparency.…”

X‐Shaped Alignment of Chromophores: Potential Alternative for Efficient Organic Terahertz Generators

“…For example, using hydrogen bonds in molecular crystals based on a quasi‐1D nonlinear optical chromophore (1‐(4‐nitrophenyl)pyrrolidin‐2‐yl)methanol (NPP), a near optimal molecular ordering angle θ p (58.6 o ) for maximal off‐diagonal component of the macroscopic optical nonlinearity has been achieved and successfully employed to demonstrate optical parametric oscillation at near‐infrared wavelengths 30,31. On the other hand, introducing octupolar 2D chromophores into crystals shows another alternative for obtaining large off‐diagonal optical nonlinearity for efficient optical‐to‐optical frequency conversion and electro‐optic effect 32–36. Achieving a high off‐diagonal macroscopic optical nonlinearity in bulk crystals needs an improvement for more efficient photonic applications as discussed below.…”

Filtering of matter symmetry properties by circularly polarized nonlinear optics

“…To experimentally illustrate nonlinear light-matter symmetry filtering, microscopy experiments were conducted on microcrystals using circular polarizations. Microcrystals of 1,3,5-tricyano-2,4,6-tris(p-diethyl-aminostyryl)bezene (TTB) [26] and NaCl were imaged using second-order (SHG) and third-order (FWM) nonlinear processes. The TTB crystals were obtained by evaporation [26] and NaCl crystals were prepared by spraying saturated salt water on a cover glass.…”

“…Microcrystals of 1,3,5-tricyano-2,4,6-tris(p-diethyl-aminostyryl)bezene (TTB) [26] and NaCl were imaged using second-order (SHG) and third-order (FWM) nonlinear processes. The TTB crystals were obtained by evaporation [26] and NaCl crystals were prepared by spraying saturated salt water on a cover glass. The crystal samples were covered with oil for index-matching purposes.…”

“…Figure 1 shows I 1 and I 3 images obtained with SHG on TTB microcrystals of needle shapes. These molecular crystals are known to be octupolar crystals oriented perpendicularly to their major axis [26]. Due to the crystal orientations, the planar octupolar symmetry is perpendicular to the propagation axis, which leads to unidirectional symmetry in the sample plane.…”