Excited-state relaxation of dendrimers functionalized with terminal cyanoazobenzene-type groups was studied by means of fluorescence and femtosecond transient absorption spectroscopy. We compare the relaxation dynamics with that of azobenzene molecules in solutions and conclude that the excited-state relaxation is determined by the excited state twisting of terminal groups, which takes place on a time scale of several picoseconds. The twisting dynamics only slightly differs in solutions and in solid film, which indicates that conformational motions during the twisting reaction are only weakly coupled to the environment. (C) 2009 Elsevier B. V. All rights reserved.