OPTICAL-PROPERTIES AND LONG-LIVED CHARGED PHOTOEXCITATIONS IN POLYDIACETYLENES

We have studied the vibrational and electronic structure and the eleme ntary excitations of poly [1,6-di(N-carbazolyl)-2,4-hexadiyne] (polyDC HD), poly[1-(N-carbazolyl)penta-1,3-diyn-5-ol] (polyCPDO), and poly[1- (N-carbazolyl)penta-1,3-diyn-5-acetoxy] (polyCPDA) by electronic absor ption, Raman scattering, and photoinduced absorption in the infrared r egion. The long-lived photoexcitations are charged bipolarons with ass ociated infrared-active vibrational (IRAV) modes. The results are also discussed in relation to the degree of chain order of the different p olydiacetylenes as evidenced by the electronic spectra. Only poly(DCHD ) shows an absorption spectrum dominated by a single exciton, suggesti ng a one-dimensional ordered structure. Consequently, for this polymer only, triplet excitons with a lifetime of the order of ms are photoge nerated in addition to bipolarons. Among polydiacetylenes, only poly(C PDA) shows photoinduced IRAV modes not affected by Fano coupling betwe en electronic and vibrational states.