Azobenzene-Containing Supramolecular Polymer Films: Laser-Induced Surface Relief Gratings

Supramolecular chemistry has developed very fast since Cram, Pedersen and Lehn received the Nobel Prize of Chemistry in 1987, which is considered as one of the most important headstreams of new concept and high tech in 21th century. Supramolecular polymer chemistry as the crossed subject of supramolecular chemistry and macromolecular chemistry, is drawing much attention of the researchers'.Now, most researches about supramolecular polymer are focused on the design and characterization of the new architectures. But there is so little work about functional supramolecular polymer. To endow the function to supramolecular polymer, we synthesized a new azobenzene compound hexahexanoyl 4,4'-dimelaminoazobenzene (He-Diazine-Azo) with self-complementary quadruple hydrogen bonds. The azobenzene in He-Diazine-Azo can undergo trans-cis photoisomerization efficiently. Using such a building block, we prepared azobenzene-containing supramolecular polymer films based on multiple hydrogen bonds. In addition, it is found, interestingly, that surface relief gratings(SRGs) can be laser-induced on such azobenzene-containing supramolecular polymer films. The supramolecular polymer films can keep good stability until 100 °C. On the other hand, to avoid the tedious synthesis of azobenzene-containing polymers, the method of doping normal polymers with azobenzene-type compounds has been introduced for the photofabrication of SRGs. However, as there is no specific interaction between the polymer and dopants in the mixing systems, the azo compounds can be molecularly dispersed in the system only when the doping concentration is low. As a result, the saturated modulation depth is usually low for the mixing systems. To resolve such a problem, we wondered if the concept of supramolecular polymers can be applied in doping systems for the realization of incorporating azo chromophores to polymeric chains, then making for large modulation depth. We developed a new approach for fabricating SRGs employing hydrogen-bonded supramolecular side-chain azo polymer. Using such azobenzene-containing supramolecular side-chain polymer films, large surface modulation depth of 312 nm can be observed.