Relaxation behaviour of NLO chromophores grafted in hybrid sol–gel matrices

Abstract

Poled hybrid siloxane–oxide coatings synthesized through hydrolysis and condensation from tetramethoxysilane (TMOS) and N-[3-triethoxysilylpropyl]-2,4-dinitrophenylamine (TSDP) precursors have been characterized via second-harmonic generation (SHG), differential scanning calorimetry (DSG) and ²⁹Si magic-angle spinning nuclear magnetic resonance (MAS NMR) measurements. Depending on chemical composition the SHG values range between 2.5 and 10 pm V^–1. The matrix rigidity seems to have a strong influence on the relaxation behaviour of the optically non-linear chromophores grafted in these hybrid networks. The glass-transition temperatures of the hybrid coatings increase with the TMOS content and the thermal curing time. These modifications can be explained by an increase in the condensation and degree of crosslinking of siloxane and silica species.