Photoexcited states in epitaxially oriented polydiacetylene films

We report the optical properties and photoinduced absorption spectra of oriented poly [1,6-di(N-carbazolyl)-2,4-hexadiyne] (polyDCHD) grown by molecular epitaxy on a crystal of potassium acid phthalate. The absorption spectra in polarized light show the high degree of alignment of the polymeric chains obtained by this growth technique. The photoinduced absorption spectra show the typical structures (due to bipolarons and triplet excitons) already observed for the same polymer as a microcrystalline sample. The photoinduced signal is maximum when the pump beam is polarized perpendicularly to the chain axis direction. This is indicative of a direct interchain long-lived carrier generation, as already observed in other oriented conjugated polymers.