Computational and experimental studies of azobenzene dendrons for non-linear optical applications

Non-linear optical dendritic macromolecules, called azobenzene dendrons, have been synthesized, and their conformational properties have been clarified by molecular dynamics calculation and second-order non-linear optical measurement. Synthesized molecules were modified by adding an azobenzene branching unit as a second-order non-linear optical chromophore and placing aliphatic chains at the chain end. Energetic results obtained by molecular dynamic calculations indicated that azobenzene dendrons tend to form a molecularly assembled structure rather than a spreading or spherical one. The first-order molecular hyperpolarizability was measured to be 3010×10^-30 esu for an azobenzene dendron having 15 azobenzene chromophores. This level of hyperpolarizability was significantly higher than that estimated when corresponding the simple additivity of a momomeric azobenzene chromophore with 150×10^-30 esu. The experimental results supported the calculated conformation of dendrons, where chromophoric units were oriented non-centrosymmetrically along the molecular axis and each of the units coherently contributed to the second harmonic generation.