Asymmetric Energy Transfer and Photo-Induced Refractive Index Modulation in Azo-Carbazole Dye Doped Polymers
Kazuhiro Tada, Daisuke Takehana, Toshiro Imai and Yutaka Kawabe
For the realization of real-time 3D display based on photo-sensitive materials as azo dyes, improvement of sensitivity and response time are strongly required. In order to improve the operational performance of candidate materials, namely azo-carbazole dyes doped in a polymer, we synthesized several azo-carbazole derivatives and studied the characteristics of light induced grating as well as strange energy exchange process observed with two-beam coupling methods. Seven types of azo-carbazoles with hydrogen, alkyl chain or hydroxyl chain at nitrogen in carbazole ring were synthesized with azo coupling reaction. Thick polymer films loading 30 wt% dye were fabricated from melted mixture. Two-beam coupling experiments showed that induced refractive index modulation and phase displacement causing energy transfer were enhanced with long alkyl chain or hydroxyl substituent. These properties suggest the importance of interaction between polymer chain and dopant molecules via hydrogen bonding or other origins, and that can be one of the reasons for high holographic performance demonstrated with azo-carbazole derivatives.
Keywords: azo-carbazole, holography, photoisomerization, photo-alignment, light induced grating, two-beam coupling, photorefractive effect