LONG-LIVED PHOTOEXCITED STATES IN SYMMETRICAL POLYDICARBAZOLYLDIACETYLENE

Photoinduced absorption is observed for the polydicarbazolyldiacetylen e in the microcrystalline state. The absorption spectrum shows well-de fined excitonic features, very similar to those observed for the same polymer in the single-crystal form. Photoexcitation at 2.54 eV gives r ise to a structured luminescence emission with the maximum around 1.7 eV. The photoinduced absorption spectrum shows three well-resolved pea ks at 0.81, 0.96, and 1.26 eV, a shoulder at 1.04 eV, and a band with a maximum below 0.3 eV. By analyzing the dependence of the photoinduce d signals on temperature, laser intensity, phase detection, and choppe r frequency, we demonstrate that the long-lived photocarriers associat ed with the peaks at 0.81 eV and below 0.3 eV are charged bipolarons. The 0.96- and 1.04-eV bands are tentatively assigned to vibronic excit ations of the bipolarons. Moreover, the 1.26-eV band has been assigned here to a triplet exciton transition. The existence of a correlation between the type of long-lived photogenerated defects and the polymer disorder is also discussed.