The geometric structures of four generations of novel azobenzene dendrimers in chloroform solution and a model of monolayer Langmuir-Blodgett (LB) film have been calculated by using a molecular dynamics (MD) method. On the basis of the MD-calculated structures of the dendrimers, the first-order hyperpolarizabilities (β) and UV-vis absorption spectra were calculated by using the semi-empirical molecular orbital, complete neglect of differential overlap for spectroscopy-configuration interaction level of theory. It is found that the rod-shaped dendrimers have significantly large β values in the solution. The β values (for incident light with λ = 1064 nm) for the second, third, and fourth generations in chloroform are respectively 2.0, 6.5, and 9.1 times that for the first one (75 × 10-30 esu). This trend is in good agreement with experimental results, though the experimentally observed enhancement of the second harmonic generation (SHG) activity is not reproduced. It is assumed that the β values of the dendrimers in the LB films are smaller than those in the solution because the azobenzene chromophores in the films have staggered conformations.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physical and Theoretical Chemistry