Efficient, Thermally Stable, Second Order Nonlinear Optical Response in Organic Hybrid Covalent/Ionic Self-Assembled Films

Abstract

A covalent/electrostatic layer-by-layer self-assembly method was used to achieve polar ordering of a water soluble, reactive dye in the fabrication of nonlinear optical (NLO) films. We observed a quadratic relationship between the second harmonic intensity I 2ω and bilayer number for all films made with Procion Brown MX-GRN, demonstrating that the polar ordering of the chromophores is consistent in each successive bilayer. As the ionic strength of the dye deposition solution was increased to 0.5 M NaCl, the of the films increased by approximately 250% to 50 × 10-9 esu, with a corresponding average chromophore tilt angle of 38°. This was attributed to increased shielding of the dye charges which led to higher chromophore density in the bilayers. The electrooptic coefficient for films of 50 bilayers fabricated at 0.5 M NaCl was 14 ± 2 pm/V. Importantly, these films exhibited excellent thermal stability, with only a 10% decrease in (I 2ω)1/2 after 36 h at 85 °C and then 24 h at 150 °C. Furthermore, the (I 2ω)1/2 recovered completely upon cooling to room temperature. These results with a commodity textile dye point to the potential value of this class of reactive chromophores and this self-assembly method for fabrication of electrooptic materials at ambient conditions from aqueous solutions.

Proposal and analysis of a silica fiber with large and thermodynamically stable second order nonlinearity

“…As a result, the nonlinearity of the Procion Brown film was found to be dominated by the zzz component, with zzz ͑2͒ = 14 pm/ V, approximately half the value of LiNbO 3 . 12 The self-assembled films exhibit excellent temporal and thermal stabilities with no decrease of zzz ͑2͒ after a temperature cycle to 150°C for 24 h or under ambient conditions for more than two years. 12 They are also mechanically stable and impervious to immersion in water or most organic solvents.…”

“…12 The self-assembled films exhibit excellent temporal and thermal stabilities with no decrease of zzz ͑2͒ after a temperature cycle to 150°C for 24 h or under ambient conditions for more than two years. 12 They are also mechanically stable and impervious to immersion in water or most organic solvents. We can directly apply this hybrid self-assembly approach and coat a tapered cylindrical silica fiber with nonlinear molecules, therefore producing the proposed nonlinear fiber illustrated in Fig.…”

“…Using this hybrid approach, a planar glass substrate coated with hundreds layers of nonlinear molecules such as Procion Brown MX-GRN has been experimentally fabricated. 12 Through second harmonic generation ͑SHG͒ measurements, the Procion Brown molecules were determined to be aligned predominately along the normal direction of the glass substrate ͑z axis͒. As a result, the nonlinearity of the Procion Brown film was found to be dominated by the zzz component, with zzz ͑2͒ = 14 pm/ V, approximately half the value of LiNbO 3 .…”

Optical Properties of Hybrid Organic‐Inorganic Materials and their Applications

“…Layer-by-Layer approach combined with the sol-gel process allows easy access to self-oriented materials. [301,302] In this case the orientation can be induced by the strong repulsive forces between the negatively charged ZrO 2 and the sulfonate groups of the chromophore (Figure 26). [301] Such method can be extended to wide range of optical materials and more generally light activated systems combining for instance nanoparticles, dyes, polyoxometallates with polyelectrolytes.…”

Polar orientation of a pendant anionic chromophore in thick layer-by-layer self-assembled polymeric films

“…Finally, films fabricated using a hybrid covalent/ionic self-assembled technique have also exhibited excellent thermal stability at temperatures as high as 150°C for 24 h and temporal stability for over 14 months under ambient conditions. 25 The sample maintained 90% of the SHG signal upon heating for 24 h at 150°C and completely recovered after cooling to room temperature; the change at elevated temperature was believed to be due to trans-cis isomerization of the azobenzene chromophore.…”