We investigate at TD-DFT/PBE0/6-31+G(d,p) level of theory, the two lowest B-u states of the trans isomer of stilbene and two stiff-stilbenes, whose phenyl rings are blocked in the molecular plane by alkylic bridges. and whose two first B-u bands have been observed. At the Franck-Condon point, computations have been performed both in gas and in condensed phase by PCM method. and the results for the two stiff-stilbenes are in very good agreement with the experiments, predicting a strongly absorbing B-u state with a main HOMO --> LUMO character and, about 0.6-0.7 eV higher in energy, a second weak absorbing B-u state, combination of the two HOMO --> LUMO + 1 and HOMO-1 --> LUMO excitations. A very similar picture is predicted for trans-stilbene in agreement with the experimental data and estimate. The dependence of the vertical excitation energies oil the C-C ethylenic bond-distances and on the rotation of the phenyl rings has been explored for trans-stilbene in gas phase. (C) 2004 Elsevier B.V. All rights reserved.