Alkoxy chain number effect on the mesomorphism, photophysical and gelation properties in aroylhydrazone-based mesogens

We report the synthesis, mesomorphic, photophysical and gelation behaviour of three series of aroylhydrazone-based polycatenars equipped with amide and ester linkages. All the series had two alkoxy chains at 3- and 5-positions at the amide end and the number and position of alkoxy chains at the ester end were sequentially increased. It was observed that the first series with alkoxy chain at 4-position at the ester end showed columnar oblique mesophase. Next, the series with alkoxy chain at 3- and 5-positions at the ester end showed columnar hexagonal mesophase. Further, the series with alkoxy chain at 3-, 4- and 5-positions at ester end showed columnar hexagonal mesophase. Similar absorption and emission spectra were observed for all the series. Only one compound showed gelation property with critical gelation concentration CGC (wt %) 1% or less than 1% in decane, dodecane and hexadecane. The FESEM image of the morphology of the gel showed a highly entangled network of nanofibers of several micrometres in length. Such mesogenic xerogels have immense potential for applications in optoelectronic devices.

本研究报道了三类带有酰胺与酯键的芳酰腙基多尾链化合物的合成、介晶相行为、光物理性能及凝胶化特性。所有系列的酰胺端均在3位与5位引入两条烷氧基链，而酯端的烷氧基链数目与取代位置依次递增。研究发现，酯端仅在4位带有一条烷氧基链的第一类系列呈现出柱状斜列介晶相；酯端在3位与5位带有烷氧基链的第二类系列呈现出柱状六方介晶相；进一步地，酯端在3、4、5位均带有烷氧基链的第三类系列同样呈现出柱状六方介晶相。所有系列的吸收光谱与发射光谱均表现出高度相似性。仅有一款化合物在癸烷、十二烷与十六烷中表现出凝胶性能，其临界凝胶浓度（critical gelation concentration, CGC）（质量分数，wt%）不高于1%。该凝胶形貌的场发射扫描电子显微镜（Field Emission Scanning Electron Microscopy, FESEM）图像显示，其呈现出高度缠结的纳米纤维网络结构，单根纳米纤维的长度可达数微米。这类介晶干凝胶在光电器件领域具备极高的应用潜力。