INDUCTION OF SMECTIC A PHASES BY ELECTRON DONOR-ACCEPTOR INTERACTION BETWEEN CALAMITIC MESOGENS AND 2,4,7-TRINITROFLUORENONE

The mesomorphic properties of conventional rod-like liquid crystals (d iphenyl-1,3,4-thiadiazoles, diphenylpyrimidines, diphenyltriazines, di phenyltetrazines and p-terphenyl derivatives), of macrocyclic liquid c rystals and of dimesogens can be influenced by addition of the electro n acceptor 2,4,7-trinitrofluorenone (TNF). Thereby nematic and smectic C phases are suppressed and smectic A phases can be stabilized or ind uced. Long and branched terminal chains result in a strong stabilizati on of the S-A phase, whereas no smectic phase is induced to accompany the nematic phases of mesogens with short terminal chains.