Synthesis and Relationships between the Nonlinear Optical and Holographic Properties of Dual Functional Azocarbazole Chromophores Based on Photorefractive Polymers

Two kinds of dual functional carbazole-based chromophores are synthesized to enhance the photorefractive (PR) performance of the polymers by attaching the electron-donating and electronaccepting groups with a diazo bridge on the 3and 6-positions of the N-ethylcarbazole. The electrondonating group is N,N-diethanol aminophenyl. The electron-accepting group is either p-nitrophenyl or 5-nitrothiazole. The peak maximum of the UV/vis absorption spectra of the 5-nitrothiazole-containing chromophore PANTAC at 535 nm is longer than that of the p-nitrophenyl-containing PANPAC at 477 nm. Both chromophores exhibit a large first hyperpolarizability in the hyper-Rayleigh scattering experiment due to the extended chain length. The first hyperpolarizability of PANTAC is 1100 × 10-30 esu, almost the double of that of PANPAC (590 × 10-30 esu). The diffraction efficiencies of both polymers are the function of the film thickness and the laser beam wavelength with a maximum ηmax at a thickness dmax between 15 and 23 μm. Surprisingly, the PANPAC-based PR polymer reveals a higher maximum diffraction efficiency (ηmax) and better fringe of the stored holograms than the PANTAC-based PR polymer does. Both the PR polymers written/read by the green/red laser have greater ηmax values than those written/ read by the green/green laser. These phenomena are related to the balance between absorption and transmission of the laser beam through the PR polymer.