p-Nitrophenylazo Calix[4]arenes, Synthesis, Monolayers and NLO-properties

Abstract
The mono, bis, tris and tetrakis (p-nitrophenyl)azo calix[4]arenes (1, 2, 3 and 4) with NLO properties are synthesized by the diazo-coupling of calix[4]arene with p-nitrophenyl diazonium. HRS measurements at 1064 nm indicate that (p-nitrophenyl)azo calix[4]arenes have higher second-order hyperpolarizability β values than the corresponding reference compound 4-(4-nitrophenylazo)-2,6-dimethylphenol, without red shift of the charge transfer band. The bis and tris (p-nitrophenyl)azo calix[4]arenes (2, 3) without hydrophobic alkyl chains can form stable Langmuri monolayers at the air/water interface because of arene π–π stacking.