Formation of a Nonlinear Optical Host–Guest Hybrid Material by Tight Confinement of LDS 722 into Aluminophosphate 1D Nanochannels

Abstract

In this work, hemicyanine dye LDS 722, is encapsulated into the 1-D elliptical nano-channels of MgAPO-11 aluminophosphate by crystallization inclusion method. The synthesis of the hybrid material has been optimized through a systematic variation of the crystallization conditions in order to obtain pure and large crystals (around 20 μm x 30 μm) suitable for optical applications. The tight fitting between the molecular size of the guest dye and the pore dimensions of the host has favored a rigid planar conformation of the dye, restricting its inherent flexibility, which is confirmed by molecular simulations. Consequently, the encapsulation of LDS 722 into MgAPO-11 has led to an astonishing enhancement of the fluorescence with respect to another analogous nanoporous aluminophosphate, MgAPO-5, with slightly larger cylindrical channels, and with respect to the dye in solution. Moreover, the perfect alignment of LDS 722 (dye with intrinsic nonlinear-optical properties) along the channels of MgAPO-11 has rendered attractive second-order non-linear properties such as second harmonic generation, proven through microscopy measurements in single crystals.