In order to enhance barriers to rotation about the C9-substituent bond in 9-s-alkyltritpycenes, the secondary alkyl group was modified as well as the peri-substituent. The barrier was slightly enhanced by modifying the substituents but the extent was rather limited. This limitation was attributed to the limitation of the ways of preparation of 9-s-alkyltriptycenes that should give three stable rotamers and carry substituents at peri-positions, where only 1,8-difluoro substituents could be used.
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