The behavior of cis-stilbene in nonvertical triplet-triplet energy transfer (NVET) reactions was examined in detail. A quantitative influence of both the single and double bond torsions on the strong NVET character was clearly evidenced by using a thermal activation model. Moreover, this model appears as powerful and remarkably fits the experimental data. The results are supported by quantum chemical DFT calculations. (C) 2004 Elsevier B.V. All rights reserved.