Molecular packing and morphological stability of dihydro-indeno[1,2-b]fluorenes in the context of their substitution pattern

Abstract

The synthesis of a series of dihydroindeno[1,2-b]fluorene (IF) derivatives with various side chain substituents is reported, these have been investigated by single-crystal X-ray analysis in terms of their molecular packings and the thermal stability of these morphologies observed by DSC measurements. It is shown that symmetrically substituted IFs bearing longer linear aliphatic side chains tend to crystallize in thermolabile coplanar layers, in which the aliphatic and dihydroindeno[1,2-b]fluorene core segments are spatially segregated. In contrast to that, the attachment of aryl side chains to the dihydroindenofluorene core results in a stabilization of the cofacial morphology, which can be observed by the absence of thermal phase transitions. In addition to this, asymmetrically substituted derivatives, so called “mixed indenofluorenes” (MIFs), bearing pairwise linear aliphatic side chains of variable length, as well as aryl substituents have been synthesized. These derivatives tend to exhibit thermostable morphologies with an enhanced tendency to form edge-to-face contacts of the dihydroindenofluorene structures.