The complexation behavior of pillar[6]arene hosts towards a carbonium ion, tropylium tetrafluoroborate (T·BF4), and the formation of novel charge-transfer (CT) inclusion complexes are described. In contrast, smaller pillar[5]arenes and larger pillar[7]arenes cannot form such complexes due to the unsuitable cavity dimensions.
![Graphical abstract: Charge-transfer inclusion complex formation of tropylium cation with pillar[6]arenes](http://hg.y866.cn/compound/lib/scimg/usr/1/C3CC42506A.jpg)
