Rigid, highly conjugated tetraalkynyl-calix[4]arenes synthesised via Sonogashira coupling give rise to improved second-order hyperpolarizability values as determined by hyper-Rayleigh scattering-a technique that in addition to X-ray crystallography also allows for the conformational analysis of the calixarene structures in solution.
![Tetraalkynyl calix[4]arenes with advanced NLO properties](https://www.iciq.org/wp-content/uploads/2014/03/Tetraalkynyl-calix4arenes_eng_noticies_articles_2005_32.gif)