Excimer formation of cyanobiphenyls in calix[4]resorecinarene derivative probed by picosecond time-resolved fluorescence spectroscopy

Excimer formation kinetics of cyanobiphenyls (CB), which are linked in a parallel direction to a calix[4]resorecinarene (CRA), has been examined by means of a picosecond time-resolved fluorescence spectroscopy. From fluorescence decay analyses, the rate constant of excimer formation is estimated to be k(3) = 1.9 x 10(9) s(-1) and that of dissociation to be k(4) = 4 x 10(7) s(-1). These values are significantly smaller than those for a liquid crystal of 4-cyano-4'-octyloxybiphenyl (80CB). The parallel orientation of CB groups in CRA may hinder the excimer formation, in contrast to those in the 80CB liquid crystal in which the CB's form a weakly coupled antiparallel dimer in the ground state. (C) 1997 Elsevier Science B.V.