Ultrafast exciton dynamics in highly oriented polydiacetylene films

The nonlinear optical response in uniaxially oriented films of poly[1.6-di(N-carbazolyl)-2, 4-hexadiyne], epitaxially grown on a potassium acid phthalate single crystal, has been measured by femtosecond pump and probe. A fast initial relaxation and the formation of long-lived species at high excitation intensities have been observed. A high third-order nonlinear optical susceptibility of 2×10−7 esu has been estimated at 627 nm. The effects of sample orientation on the relaxation dynamics have also been investigated.