Orientational distribution of SHG chromophore on polyimide LB film

The Langmuir-Blodgett (LB) films composed of N,N-diphenylamino-p-nitrostibene as a side chain of polyimide were prepared by the precursor method. Oblique incident surface SHG measurements from the LB monolayers before and after the imidization provided the symmetries and nonlinear-optical tensor components of the LB films. From the obtained orientational distribution functions (ODFs) of the monolayer before and after the imidization process, it was found that the polar angle of the side chain increases by the imidization and this causes the decrement of the nonlinear optical components. But the half-width (Δθ) of the major molecular tilt angle decreases by the imidization suggesting that the chromophore is more closely packed.