Activated crystals of pillar[6]arene produced by removing the solvent upon heating were able to take up branched and cyclic alkane vapors as a consequence of their gate-opening behavior. The uptake of branched and cyclic alkane vapors by the activated crystals of pillar[6]arene induced a crystal transformation to form one-dimensional channel structures. However, the activated crystals of pillar[6]arene hardly took up linear alkane vapors because the cavity size of pillar[6]arene is too large to form stable complexes with linear alkanes. This shape-selective uptake behavior of pillar[6]arene was further utilized for improving the research octane number of an alkane mixture of isooctane and n-heptane: interestingly, the research octane number was dramatically improved from a low research octane number (17 %) to a high research octane number (>99 %) using the activated crystals of pillar[6]arene.

Activated crystals of pillar [6]arene produced by removing the solvent upon heating were able to take up branched and cyclic alkane vapors as ac onsequence of their gate-opening behavior.T he uptake of branched and cyclic alkane vapors by the activated crystals of pillar [6]arene induced ac rystal transformation to form one-dimensional channel structures.H owever,t he activated crystals of pillar-[6]arene hardly took up linear alkane vapors because the cavity sizeo fp illar [6]arene is too large to form stable complexes with linear alkanes.T his shape-selective uptake behavior of pillar[6]arene was further utilized for improving the researchoctane number of an alkane mixture of isooctane and n-heptane:i nterestingly,t he researcho ctane number was dramatically improved from al ow researcho ctane number (17 %) to ah igh researcho ctane number (> 99 %) using the activated crystals of pillar[6]arene.Separation of linear and branched alkanes is of significant important in the petroleum chemistry.T he branched alkanes in the 5-7 carbon number range are major components in high-octane gasoline because they have high research octane numbers (RONs). Fore xample,2 ,3-dimethylbutane,2 ,2dimethylbutane,a nd isooctane have RONs of 101.7, 91.8, and 100, respectively.Incontrast, RONs of linear alkanes are quite low.The RONs of n-hexane and n-pentane are 24.8 and 0, respectively.F urthermore,q uality of gasoline is evaluated in the RON,w hich is the volume ratio of isooctane in am ixture of isooctane and n-heptane in gasoline.H owever, the boiling point of isooctane (b.p.: 99 8 8C) is almost the same as that of n-heptane (b.p.: 98 8 8C), so the separation of these two alkanes via petroleum distillation is very difficult, and many manufacturing processes are required to produce gasoline with ahigh RON. [1] Separation of linear and branched alkanes using adsorption materials is one of the most energy-efficient strategies. This has been achieved with chromatography systems that use columns packed with microporous materials such as zeolites, [2] carbon molecular sieves, [3] and metal-organic frameworks (MOFs) also been called porous coordination polymers (PCPs). [4] However,a lkanes have low affinity with these materials because they only have low polar C À Ca nd C À H groups.T hus,s eparation of liner and branched alkanes using the chromatography systems is atime-consuming process,and an ew energy-efficient separation protocol should be developed. Separation by adsorption materials that undergo ac rystal transformation should be ap romising strategy for the separation of analogous molecules [5] because the separation with crystal transformation enables isolation of at arget compound with high purity,i se asy-to-handle,a nd energyefficient. However,tothe best of our knowledge,isolation of branched alkanes from am ixture of linear and branched alkanes by means of this sort of separation procedure has not been achieved yet.Herein, we demonstrate that isolation of branched alkanes from am ixture of linear and branched alkanes using a...