Azobenzene derivatives in or bound to polymer show photoinduced birefringence and dichroism under polar light excitation through trans-cis isomerization and following reorientation of the molecules, sometimes being succeeded by macroscopic deformation as surface reliefs. In general, the transition process begins with the angular hole burning due to selective isomerization of the molecules aligned parallel to the light field, being followed by directionally random molecular reorientation in relaxation. As most of preceding studies were made with optical Kerr effect and four wave mixing, signal intensities reflected the difference between two index components and two regions, respectively, making it difficult to discriminate the temporal evolution of respective optical constant components.
In this study, to elaborate the elementary processes, simple material system as DR1 doped PMMA was employed and in situ measurement of absorption spectrum and its polarization dependence were made under and after the excitation with linearly polarized light. The results indicated that the absorbance reduced strongly when the probe light was parallel to the pump, and that in perpendicular direction it also reduced with one-thirds amount of the counterpart. It showed that the angular hole burning process was dominant and reorientation effect made less contribution to the dichroism, contrary to common understanding. Estimation of extinction coefficient modulation caused by both mechanisms was made based on a simple model. Quantum efficiency of photoisomerization, longtime stability, dye concentration dependence, comparison to induced birefringence, and comparison between doped polymer and side chain polymer will be discussed.
Yutaka Kawabe and Kento Okoshi, "Discrimination between photoisomerization and molecular reorientation processes in azo dye-doped polymer (Conference Presentation)," Proc. SPIE 10529, Organic Photonic Materials and Devices XX, 1052910 (Presented at SPIE OPTO: February 02, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2286050.5752200751001.
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