Investigation of the Intra-CH/π Interaction in Dibromo-9,9′-dialkylfluorenes

Abstract

Polyfluorenes are well-known derivatives that exhibit electrical conductivity, electroluminescence, and liquid crystallinity, but its crystallization process is not well understood. To investigate the role of intra-CH/π interaction in the process, 2,7-dibromo-9,9′-dialkylfluorenes (DBFs) with various dialkyl side chains (alkyl group = methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-octyl, 2-methylpropyl, and 2-ethylbutyl) were prepared. Systematic observation of the single-crystal structure revealed that DBF with a methyl group does not possess intra-CH/π interactions, whereas DBFs with straight side chains that are equal to or longer than an ethyl group exhibit CH/π interactions between Hβ and the fluorene ring. For DBFs with branched side chains, one Hβ and one Hγ interact with the fluorene ring. The computations at the MP2/cc-pVTZ//MP2/6-31G(d) level with a polarizable continuum model revealed that the close proximity of Hγ and the fluorene ring in the branched DBF crystals was caused by the geo...