Preparation of chromophoric dipolar dendrons as second-order nonlinear optical material

Dendritic macromolecules, called `dendrons', having a branching structure modified with an electron donor/acceptor functionalized azobenzene chromophore have been synthesized. The structurally different dendrons possess different numbers, 1, 3, 7, and 15, of chromophore units. The second harmonic generation (SHG) of dendrons was measured in the molecular oriented thin films prepared by the Langmuir-Blodgett film transfer technique. In such structurally organized thin films, individual chromophores coherently contribute to the increase in the molecular hyperpolarizability of dendrons. The SHG activity became large as the numbers of branching units of dendrons increased. The highest molecular hyperpolarizability was found to be >8000×10^-30 esu for dendron containing 15 chromophoric units. The SHG results suggest that the structure of dendrons synthesized is uniaxially dipolar, and that there is a particular merit in this structure for the generation of SHG.