Thermal hysteresis is a phenomenon, in which different responses occur during heating and cooling. Although bulk materials can exhibit thermal hysteresis by strong and multiple cooperative interactions between molecules, thermal hysteresis at molecular level in nonpolar organic solvents was essentially not known until now. We found that a chiral sulfonamido helicene tetramer forms a helix dimer in 1,3-difluorobenzene, which unfolds to a random coil on heating. This structural change exhibited thermal hysteresis, in which different structures of a helix dimer and a random coil were formed during heating and cooling at the same temperature. The phenomenon was explained by the different populations of helix dimers and random coils at the same temperature, and by the presence of induction periods. Thermal hysteresis is related to the "memory effect": the molecules memorize their thermal history, whether they were heated or cooled in the past. The model can also explain the "memory effect".
|出版ステータス||Published - 2013 9 1|
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