The syntheses and reactions of photoresponsive dendrimers are described. Dendrimers with photoreversible stilbene cores undergo mutual cis-trans isomerization in organic solvents to give photostationary state mixtures of cis- and trans-isomers. Even stilbene dendrimers with molecular weights as high as 6500 underwent mutual cis-trans isomerization within the lifetime of the excited singlet state. The large dendron group surrounding the photoreactive core may affect the excited state properties of the core to induce the efficiency of photoisomerization and/or reduce the fluorescence efficiency. The photochemistry of stilbene dendrimers, with various types of dendron groups, azobenzene dendrimers and other photoresposive dendrimers is discussed. (C) 2004 Japanese Photochemistry Association. Published by Elsevier B.V. All rights reserved.