a b s t r a c tA series of single Q2 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.

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Topography-dependent tuning of water wettability was achieved on a stainless steel surface textured by nanosecond-laser pulses at different laser fluences, with the minimal contribution of the surface chemical modification. Such differently-wet neighboring surface spots were demonstrated to drive an autonomous directional water flow. A series of elementary microfluidic devices based on the spatial wetting gradients were designed and tested as building blocks of “green”, energy-saving autonomous microfluidic circuits.

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The mol­ecule of the title compound, C15H18N4, adopts a trans conformation with respect to the diazo N=N bond. The dihedral angle between the benzene and pyridine rings in the mol­ecule is 8.03 (5)°. In the crystal, a weak C—H⋯π inter­action arranges the mol­ecules into a corrugated ribbon, with an anti­parallel orientation of neighboring mol­ecules propagating in the [100] direction.