Articles First Photosensitive Liquid Crystalline Dendrimer: Synthesis, Phase Behavior, and Photochemical Properties Natalia Boiko, Xiaomin Zhu, Alexey Bobrovsky, and Valery Shibaev* Chemistry Department of Moscow State University, Leninskie gory, Moscow, 119899 Russia Received July 3, 2000. Revised Manuscript Received November 27, 2000 The first photosensitive liquid crystalline (LC) dendrimer with terminal cinnamoyl groups was synthesized. A new approach to the synthesis of photochromic carbosilane LC dendrimers was elaborated. The method consists of synthesis of dendrimer with terminal hydroxyl groups and then coupling of 4-methoxycinnamoyl chloride to it. It was shown that the LC dendrimer of the first generation forms a smectic A (SmA) phase. The photochemical behavior of the dendrimer in dilute solution and in films was studied. The experimental data show that at least two processes, E-Z photoisomerization and [2+2] photocycloaddition leading to the formation of the three-dimensional network, take place. Introduction A dendrimers is a macromolecule with a regular tree- like array of branching units. Numerous dendritic structures have been synthesized and studied, including polyamidoamines, 1 polyamides, 2 polyphenyl ethers, 3 and carbosilanes. 4 In recent years, dendrimers with different designed functionalities have become objects of particu- lar academic and practical interest because of their unique superbranched architectures, high densities of peripheral functionalities, symmetrical shapes, and monodispersity. Such compounds have units that are capable of performing specific functions, such as electron- transfer processes (transition metal units 5 ), antenna effects (chromophoric groups 6-10 ), and photoinduced processes (photoisomerizable groups 11-16 ). 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