Enhanced circular dichroism at elevated temperatures through complexation-induced transformation of a three-layer
Ryo Katoono1, Yudai Obara1, Kenshu Fujiwara1
1Department of Chemistry , Faculty of Science , Hokkaido University , Sapporo 060-0810 , Japan . Email: katoono@sci.hokudai.ac.jp ; ; Tel: +81 11 706 3396.
Abstract:
When two planes stacked one above the other are twisted, they provide a dynamic pair of helical conformations with (M)- or (P)-helicity. We designed a three-layer cyclophane that consists of two such dynamic pairs: the top and middle planes, and the middle and bottom planes. Hence, several global conformations could be created for the overall molecule, e.g., double-helical forms with a pair with the same helicity [(M,M) or (P,P)], and a meso-like form with a pair with a different helicity (M,P). These conformations dynamically interconvert to each other in solution. Chiroptical properties were given by the helical-sense preference of the double-helical forms, which was brought about through complexation with a chiral hydrogen-bonding guest. In terms of the conformational energy in a complexed state, when a desirable relationship between double-helical and meso-like forms was attained, complexation-induced circular dichroism was enhanced at elevated temperatures and decreased at lowered temperatures.
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