Synthesis and conformational studies of a series of 5,17-bis-aryl-25,26,27,28-tetrapropoxycalix[4]arenes: the influence of pi-pi interactions on the molecular structure

Four 5,17-bis-aryl-25,26,27,28-tetrapropoxycalix[4]arenes were prepared via Negishi, Suzuki and Ullman type couplings [aryl = phenyl (1), 3-bromopheny l (2), 1-naphthyl (3) and carbazol-9-yl (4)]. The influence of the aryl gro ups on the structure was studied by X-ray crystallography, NMR, electronic absorption and fluorescence spectroscopy. The results show a drastic differ ence in conformation where 1 and 2 prefer to have the substituents away fro m each other while 3 and 4 have them in close contact. The photophysical pr operties of 3 and 4 exhibited a very solvent dependent fluorescence.