Synthesis of oligofluorenes by endcapping

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Abstract
An efficient one‐step synthesis of 9,9‐di(2‐ethylhexyl)‐2,7‐fluorene oligomers via an endcapping reaction is reported. Controlled endcapping demands a full conversion of functional groups and thus the Yamamoto reaction was chosen as the aryl–aryl coupling method. SEC analysis showed that the endcapping is complete. The molecular weights were adjusted in the range from 1300 to 3800 g mol−1 by different amounts of endcapper. The mixtures exhibit broad mesophases and the transition temperatures strongly increase with molecular weight. In the series of oligomers reported here, clearing temperatures between 57°C and over 360°C could be realized.