2ND HARMONIC-GENERATION BY THE SELF-AGGREGATION OF ORGANIC GUESTS IN MOLECULAR-SIEVE HOSTS

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. © 1990, American Chemical Society. All rights reserved.