Second Harmonic Generation by the Self-Aggregation of Organic Guests in Molecular Sieve Hosts

Abstract

Inclusion of polar organic molecules in molecular sieve hosts has been investigated as a means of creating self-assembled aggregates of molecules that possess the noncentrosymmetry required for materials to exhibit second harmonic generation (SHG). Aluminophosphate molecular sieves with one-dimensional channel structures are shown by SHG powder measurements to successfully direct this self-aggregation for a number of organic molecules including and related to p-nitroaniline. Models supported by FTIR evidence show the aggregates could be chains of molecules with a large net dipole that form within the molecular sieve channels. The polar host crystal then aligns the aggregates to produce a large bulk dipole moment and the observed SHG signal. Three methods for controlling the SHG intensity within a particular host structure have been elucidated: (1) variation of guest concentration, (2) alteration of guest structure, and (3) changing the charge density on the host framework.

Enhanced Second-Order Optical Nonlinearity of Dye Molecules Adsorbed onto Laponite Particles

“…First, the requirements for materials to be used in device applications that utilize nonlinear interactions are very demanding. New approaches to materials research can yield materials with favorable properties compared to traditional nonlinear materials, as shown recently in several supramolecular systems (Cox et al 1990;Stucky and MacDougall 1990;Clays et al 1993;Kelderman et al 1993;Kauranen et al 1995;Lehn 1995). This is particularly true for 2nd-order nonlinear optics that require noncentrosymmetric materials (Prasad and Williams 1991).…”

3-D Periodic Packaging: Sodalite, a Model System

“…Molecular self assembly has been monitored both on the external surface of zeolites by atomic force microscopy(AFM) (39) and within the pores by second harmonic generation. Orthogonal self assembly within the 3-d pores has been demonstrated by co-inclusion of two types of organic guests which have diametrically opposed non-linear optic responses (40),(41), (42). For example, para nitroaniline (NA) has a zero SHG response in the bulk since it is centrosymmetric, but can be oriented by the host channel polar axes of AIPO-5 to give a large SHG response.…”

The Interface of Nanoscale Inclusion Chemistry

“…In the experiments described by Cox et al (214) both centrosymmetric and noncentrosymmetric hosts were tried. Significant polar alignment was observed only with noncentrosymmetric hosts.…”