科研之友
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摘要
Many modern systems are based on photoresponsive materials, in which properties such as the refractive index need to be effectively controlled. An extensively used means of achieving this is to photoinduce birefringence by alignment of anisotropic azochromophores via light-induced isomerization. However, the refractive index changes are typically small (<10(-2)), slow (seconds or minutes) and not spontaneously reversible, which excludes use of this approach in a variety of optical systems. The drawbacks are generally attributed to hindered photoalignment due to the molecular environment, which suggests that optimizing the arrangement of the functional moieties to minimize the mobility restrictions could decisively improve the photoresponse. Here, a simple solution-processing approach is reported for favorable distribution at the molecular level of neat azochromophore into a three-dimensionally nanostructured hybrid system exhibiting an extremely enhanced photoresponse. The standard azoderivative Disperse Red 1 is adsorbed on silica colloidal crystals that are chosen as 3D-templates because their photonic bandgap, which is sensitive to refractive index changes, provides a direct tool to study photostimulated processes in the chromophore. The system is thoroughly investigated with different techniques to identify molecular out-of-plane photoalignment as the main phenomenon responsible for the optical response, and to discern the key factors leading to improved performance. It is found that the dye molecules are spontaneously adsorbed on the silica spheres, building a highly photoreactive surface multilayer. A low amount of azochromophore allows for outstanding material response upon cw-irradiation, as a result of very large and fast refractive index changes in the chromophore ensemble (up to 0.36 - birefringence of 1.1 - in 15 ms at 0.09 J cm(-2)) that, in addition, is fully reversible by thermalization. Finally, as proof-of-principle for real applications, long-duty cycle photoswitching at 100 Hz (for over 2 million cycles) is demonstrated in this system.
- 出版日期2011-11-8
