Long-lived cis state of azocarbazole dye with strong acceptor highly doped in a polymer matrix

Abstract

In order to investigate the formation mechanism of photoinduced gratings in an azocarbazole dye, 3-[(4-nitrophenyl)]azo-9H-carbazole-9-ethanol (NACzEtOH), used for dynamic hologram, temporal variation of absorption spectra were observed after optical excitation. From a series of spectra obtained during recovering process, spectral components from two constituents were extracted analytically with a technique based on singular value decomposition. Two components were assigned to trans and cis states, by comparison to the theoretical prediction made with a molecular orbital method. Temporal evolution of two components indicated the existence of long-lived cis state with lifetime of 15 min for the most concentrated case (30 wt. % dye in matrix). The results also showed that cis state relaxed to the initial state without reorientation, suggesting an essential role of cis state population in the dynamic holography system based on azocarbazoles.