Third‐order nonlinear optical interaction and conformational transition in poly‐4‐BCMU polydiacetylene studied by picosecond and subpicosecond degenerate four wave mixing

The electronic third‐order nonlinear optical interaction in a solution cast film of a polydiacetylene has been studied by degenerate four wave mixing. The results demonstrate a subpicosecond response and a very high χ(3) value. The χ(3) value changes considerably during the thermally induced conformational transition in the film in which the effective π‐electron conjugation is reduced.