| Summary: | 碩士 === 國立清華大學 === 化學系 === 100 === A tailor-designed vanadyl methoxide complex bearing p-heptoxyphenyl group (i.e., a nematic LC like fragment) at the C5 position of the salicylidene template was synthesized and then subjected to LiVO3-induced self assembly to form loosely bound, Li+-encapsulated quadruplexes. These cluster complexes were utilized as chiral dopants (1% by weight) to nematic LC materials. A systematic survey regarding the effect of the encapsulated metal ions within the alkali family and Ag+ on the changes of helical pitch was performed and determined by Grandjean method in wedge cells viewed under polarized microscopic scope. It was found that the twisting power or helical pitch induced by a chiral quadruplex dopant is very responsive to its modulable helical shape due to its π-π and dipole-dipole interactions with a nematic LC host. By increasing the size of the encapsulated metal ion from Li+ to Rb+ in the quadruplex by dynamic metal-ion specific swapping, its four lower rim regions of the resulting cluster (i.e, the four p-heptoxyphenyl groups) get closer, thus inducing less helical twisting to the nematic LC phase. Notably, the ion size change [Rb+ (152 pm) > K+ (138 pm) > Ag+(115 pm) > Na+ (102 pm) > Li+ (76 pm)] among the encapsulated metal ions is only around 13-26 pm. This information can be asymmetrically amplified to 1.3-2.1 um pitch change in LC phase. Therefore, the overall extent of amplification reaches 100000 times in terms of helical pitch change. A linear correlation between the induced helical pitch (Y-axis) and the ionic radius of a metal ion (X-axis) was established.
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