Studies on properties of p-nitrophenylazo calix[4]arene derivatives

The p-nitrophenylazo calix[4]arene derivatives 1a-1d with nonlinear optical (NLO) properties were prepared by the diazo-coupling reaction of calix[4]arene with p-nitrophenyl diazonium. The diazotization reaction of p-nitroaniline was carried out with isoamyl nitrite as a source of nitrous acid in EtONa/EtOH under refluxing condition. X-Ray crystallographic analysis and H-1 NMR spectra reveal that they exist as cone conformation in crystal state or in solution. HRS measurements at 1064 ran in THF indicate that p-nitrophenylazo calix[4]arenes have higher hyperpolarizability beta(z) values than the corresponding reference compound 4-(4-nitrophenylazo)- 2,6-dimethyl-phenol, without red shift of the charge transfer bond. The tetrakis p-nitrophenylazo calix[4]arene (2) with longer alkyl chains can form monolayer at the air/water interface.