From p-Dimethoxybenzene toward Crown Benzenophanes: 1,3,10,14-Tetraoxaparacyclophane

Article abstract of DOI:10.1021/jo00046a038

The title compound tetraoxa<3.5>paracyclophane (6) has been prepared and studied in order to investigate the evolution of spectroscopic properties in going from the monomer unit p-dimethoxybenzene (9) via the noncyclic bichromophoric reference compound 3b to 6.The X-ray structural analysis of 6 shows that the distance between the two aromatic carbon atoms linked to the smaller bridge is shorter than the van der Waals distance.The resulting electronic interaction is reflected by the perturbation of the UV spectrum of 6 (in particular by a distinct hypochromic effect) and in its charge-transfer complexes with TCNE and TCNQ, as compared to 9 and 3b.The fluorescence quantum yields show significant quenching as compared to 9.This process is related to the formation of a new, structureless red-shifted band with a maximum at 26670 cm^-1, comparable to that of the excimer of 9.From a Stern-Volmer plot the self-quenching rate constant of the latter, k_q ca. 1.2 x 1E9 mol^-1s^-1 is derived.