The Role of the Chromophore Size and Shape on the SHG Stability of PMMA Films with Embebbed NLO Active Macrocyclic Chromophores Based on a Cyclotetrasiloxane Scaffold

Abstract

In recent years, efforts have been dedicated to the investigation of the technological properties of nonlinear optical (NLO) organic crystalline materials with the aim of their application in various electro-optical devices, such as optical waveguides. 1 However, it is quite difficult to produce electro-optical devices starting from organic crystalline materials. For such a reason, in the last two decades, many investigations on composite NLO materials based on organic or organometallic second order NLO molecular chromophores embedded in organic polymers have been developed, as an other approach to second order NLO materials, based on molecular NLO chromophores, 2 which may show attractive properties such as low dielectric constant, chemical stability, high damage threshold, fast response time, and good processability. 3 In order to induce second harmonic generation (SHG) in an amorphous thin polymeric film with an embebbed second order NLO molecular chromophore, it is necessary to apply a strong oriented electric field working at about the glass transition temperature (T g ) of the polymer (poling process). This process allows the orientation of the dipolar chromophores in regions of the polymeric microscopic framework with sufficient local free volume and segmental mobility. 4 In this way, by a preferred orientation of the molecular dipoles, a polar order is produced and the macroscopic centrosymmetry is removed. For practical uses, these composite materials should show good nonlinearity and chemical stability, and in particular a satisfactory stability in the time of their SHG.The stability in the time of the SHG of these NLO active composite polymeric materials as a function either of the poling parameters, for example, the T g of the polymer or the concentration of the NLO active chromophores, has been largely investigated. 2,3,5 However, less research has been done in order to clear the role of the size and shape of the chromophores. 1e,6 This role may be significant, since the temporal stability of the SHG is related to the relaxation dynamics of the oriented NLO chromophores in the polymeric matrix. 7 Recently, some of us reported the synthesis and second order NLO response of a series of tetrameric macrocyclic second order NLO chromophores, based on four NLO active organic tails assembled in a cone arrangement on the same face of a cyclotetrasiloxane ring. In parallel, the monomeric structurally homologous NLO chromophores have been synthesized and their second order NLO response investigated. 8 The second order NLO response of these macrocyclic NLO chromophores, measured in CH 2 Cl 2 solution as μβ 1.91 by the ABSTRACT: In this work, the second harmonic generation (SHG) and the nonlinear optical (NLO) coefficients d 33 of PMMA films, containing 4 wt % NLO active macrocyclic chromophores based on a cyclotetrasiloxane scaffold and of their monomeric structurally homologous NLO active chromophores, were obtained by an electrical poling process and measured at room temperature during a period of many mont...

Long‐Term‐Stable Strong Second Harmonic Generation in Flexible DAST−PVDF Composite Films Realized by the Interface Interactions

“…This can be attributed to the applied external electric field was insufficient to orientate the DAST molecules and carbon-fluorine bonds of PVDF in the direction of the poling field in this case, due to the high viscosity of the composite films at low poling temperature. [15] Rather differently, a preferential direction was observed in the corresponding FFT image after poling at a higher temperature of 100 °C, where the ordered arrangement direction of DAST microcrystals appears, as indicated by the red arrows in the bottom FFT image of Figure 5d. This implies that the increased mobility and local free volume in the composite films at high poling temperature (100 °C) increase the orientation rate of the DAST chromophore, thereby enhancing the SHG intensity.…”

“…Nonlinear optical (NLO) materials with high second-order NLO susceptibility χ (2) are essential to a broad range of applications such as frequency metrology, information processing, medical cyclotetrasiloxane scaffold, in which case the d 33 value of the poled composite films decreased only 14% after poling and maintained stable for 6 months. [15] Despite these achievements, the decay of the SHG intensity has remained a thorny issue for polymeric NLO composites. It calls for a better understanding of the interrelationships between their chemical structures and NLO properties, along with the materials with better scalability and processability.…”

Synthesis and Nonlinear Optical Studies on Organic Compounds in Laser-Deposited Films

“…The chemical methods include solution techniques and gas-phase deposition methods. Techniques that use solutions include Langmuir-Blodgett (LB) [68,69], spin coating [70,71], dip coating [72,73], sol-gel [74,75], and spray pyrolysis [76]. Chemical vapor deposition (CVD) [77][78][79][80][81][82] uses the gas phase of organic compounds.…”

Preparation of the Inclusion Complex-Type Nonlinear Optical Polymer

“…By combining NLO molecules with polymers, the high NLO susceptibility, fast response time, low dielectric constant, small dispersion in refractive index, structural �exibility, and ease of material processing have brought NLO polymers to the forefront of NLO research [4]. NLO polymers can be divided into guest/host polymer [5][6][7] and covalently linked polymers (side-and main-chain polymers) [8][9][10]. Guest/host polymers blend NLO chromophores (guest) to the polymer matrices (host).…”