Synthesis, characterization and optical power limiting behaviour of phenylazo- and 4-nitrophenylazo-tetrahydroxytetrathiacalix[4]arene

p-Tetrakis(4-nitrophenylazo) tetrahydroxytetrathiacalix[4] arene and p-tetrakis(phenylazo) tetrahydroxytetrathiacalix[4] arene were prepared and fully characterized using H-1 and C-13 NMR, mass spectroscopy, thermogravimetric analysis and differential scanning calorimetry. The solid-state structure of p-tetrakis(4-nitrophenylazo) tetrahydroxytetrathiacalix[4] arene was investigated by single crystal X-ray diffraction. It crystallized in the triclinic system (space group: P (1) over bar). z-Scan experiments were performed on the p-tetrakis(4-nitrophenylazo) tetrahydroxytetrathiacalix[ 4] arene showing non linear absorption due to two photon absorption with a TPA cross-section of about 50 x 10(-50) cm(4) s per photon. Optical power limiting measurements on the p-tetrakis( phenylazo) tetrahydroxytetrathiacalix[ 4] arene at 532 nm (48% linear transmission) was found to limit the energy to similar to9 muJ.