1 : 1 mixtures of aminomethylenehelicene (P)-tetramer and (M)-pentamer with terminal C16 alkyl groups in fluorobenzene showed structural changes between hetero-double-helices B and C and random-coils 2A.

A 1 : 1 mixture of aminomethylenehelicene (P)-tetramer with C 16 alkyl groups (P)-1-C 16 and (M)-pentamer (M)-2 in fluorobenzene forms hetero-double-helices, and the processes of formation and dissociation exhibit thermal hysteresis on cooling and heating. When thermal triangle waves with repeated cooling and heating cycles are applied, unstable thermal hysteresis appears, which becomes a stable thermal hysteresis after sufficient numbers of cycles. The phenomenon of middle-range stable thermal hysteresis is observed in this case. Properties of unstable and stable thermal hysteresis are examined under various thermal triangle waves.