An analysis of the torsional movement of the phenyl groups in traps-stilbene at variable temperatures in the light of the free energy changes involved was found to provide a simple explanation for the conformational behaviour of this compound. There is experimental evidence that traps-stilbene is planar at low temperatures in the gas phase, but departs from planarity as the temperature is raised. The analysis also provides an explanation for the thermochromic behaviour of the first electronic absorption band for the compound. (c) 2006 Elsevier B.V. All rights reserved.