Synthesis, crystal growth, thermal and spectroscopic studies of acentric materials constructed from aminopyridines and 4-nitrophenol

A series of single co-crystals of non-centrosymmetric complexes of different mono- and diaminopyridines, namely 4-aminopyridine, 3,4-diaminopyridine, 2-amino-6-methylpyridine, 2,6-diaminopyridine, 2-aminopyridine, with 4-nitrophenol were grown by slow evaporation technique from solution at constant temperature. Optical transparency in the region of 300-1100 nm was found to be suitable for nonlinear optical applications with cut off wavelengths at 420-474 nm for these co-crystals. Single crystal X-ray analysis confirms the non-centrosymmetric packing. Thermogravimetric and differential thermal analysis shows good thermal stability of the studied compounds with melting point at range 99-172 °C for different co-crystals. The second harmonic generation efficiency has been measured on single crystals by comparative SHG technique relative to KTP crystal. The nonlinear optical coefficient of the compounds was found to be up to 39 pm/V.