Synthesis and fluorescence behavior of calix[4]resorcinarenes possessing pyrenyl group(s)

Abstract

A mixture of octa-o-acetylated calix[4]resorcinarenes (CRAs) with varying numbers of 2-(pyren-1-yl)ethyl residues is synthesized by acid-catalyzed condensation of resorcinol with 3-(pyren-1-yl) propanal, followed by acetylation. The product is separated using reversed phase silica gel column HPLC. NMR spectra of the isolated octa-o-acetylated CRAs substituted with different numbers of pyrenyl groups revealed that all the cyclic tetramers are of the crown conformation. The product distribution is almost in accordance with theoretical values, assuming that the reaction rates of the two aldehydes are the same. ¹H NMR chemical shifts of the pyrenyl groups are shifted to an upper field with increasing number of pyrenyl groups because of the ring current effect. Measurements of steady state spectra and decay time of pyrene fluorescence of the CRAs revealed that they form two types of excimer and that strain in the excimer does not depend on the number of pyrenylethyl groups.